> Ducts are dead.

Ducted heatpumps are a thing here in NZ and make sense to me, not that I have used one. The heatpump sits in the roof and air is pushed into three or so rooms through ducts.

If building a new house I think ducts would be the way to go.

You have to think carefully about where you run the ducts. They can be a huge source of energy loss. 40% is the number quoted by the EPA.

Most roofs in Australia still aren’t sealed. The air barrier and insulation barrier is the ceiling. The roof space itself is not insulated, so the ducts are exposed to extreme temperatures, thus destroying the efficiency.

Here is just one article on it: https://newenergythinking.com/2018/10/20/dont-use-ducts/

I hadn't considered that.

My argument with split systems, at least how they are installed in NZ, is that they are usually installed in the main living area and if there is a second unit, in a corridor.

So corridors are heated or cooled far hotter or colder than they need to be in order to heat/cool bedrooms.

I have two units that are heated by heat pumps in Massachusetts.

One has mini splits. You definitely don’t generally put mini splits in every single room (like bathrooms or interior hallways) because each mini split requires tubing, is large, and expensive. No, I think it’s way more likely that you would have them in the bedrooms rather than the hallway

Exactly. In this example, which is pretty common here, I installed 1 in the living area and then 1 in each of the bedrooms.

In New Zealand I have seen small heatpumps in bedrooms, but I would have to say it is extremely rare.

But we have many very toasty hallways leading to cold single glazed bedrooms!

That might be a climate difference — it gets below 0 Fahrenheit here every winter, as I understand it, NZ is quite a bit warmer, so maybe the strategy of “heat the core of the house and let it radiate out” works.

There are historical and cultural reasons for our poorly insulated and heated homes, but "heating the core" is not one of them.

In the last few years the central govt has brought in legislation requiring landlords to heat and insulate homes to a certain standard.

Why wouldn't you just lay insulation on the ducts, same as you do with water pipes?

US and Australian units are different for insulation, but in my terms the insulation around the best ducts is R1.5, but good ceiling insulation is R6. 4x difference

Interesting. The code for duct insulation in unconditioned spaces in the US is R8, and they're pushing for higher currently.

They also recently undid a long held myth about ducts buried in insulation leading to condensation issues. Most areas now allow ducts to be buried as long as you have R19 above and below, or R30 above. When I just installed a ducted mini for 3 upstairs bedrooms, I surrounded my R8 flex duct with R30 insulation.

lol - it's not a myth. It's physics: https://www.youtube.com/watch?v=Vufih-WN5R4

Fwiw, context of this video is metal duct work. You’re not going to see R-8 flex duct buried in R-30 begin to sweat when the AC is running. In terms of controlling the dew point, the duct is no different than the conditioned space at that point.

Like you said, it’s physics.

Over insulation introduces new problems like condensation (which causes mold and other nastiness)

https://www.youtube.com/watch?v=Vufih-WN5R4

Your statement is quite context dependent, and does not apply to most modern residential scenarios. “Over insulating” a flex duct is not going to cause condensation. Metal duct work in an unconditioned space can cause condensation. Wrapping it in (often thin) fiberglass insulation can increase condensation in certain conditions. Improperly vented attics (and/or air leakage from conditioned space) with metal ducts can cause issues.

I thought this was absolutely the solution but backtracking a little now based on experience so far.

We have a two-level, five bedroom new build in Auckland which came with a single-zone ducted system. So outputs are the bedrooms plus upstairs and downstairs lounges. The vents are tidy and unobtrusive - much less space than a wall unit in each location.

We're having major issues balancing the temperature across the different rooms as there is one thermostat.

Think setting the temperature overnight for one room with a couple plus a cat vs another room with one of the kids. Basically the wife and I are always far too hot because otherwise we're freezing all the other rooms. Or setting a reasonable temperature in the lounge makes all the rooms icy in short time.

I'm now thinking about forking out the couple of thousand to get a small heat pump installed directly into our room so we can run it separately from the rest of the house.

So if building from scratch, either look into a multi-zone system or separate heatpumps. If you can get separate systems but hidden in the walls/roof that would be the best.

I had a similar problem, but I decided that simply running the fan to mix up the air was a fine solution. The fan doesn't use much electricity, and it's good not to let rooms get too stale anyway.

I have the fan programmed to run 10 or 15 minutes an hour regardless of if the heat pump needs to run. It keeps things pretty even.

Can't you choke down the airflow from your bedroom duct?

What about in-line duct fans or even register fans in the rooms that are not heated/cooled appropriately:

https://www.amazon.com/AC-Infinity-Register-Thermostat-Contr...

Appropriately placed In-line duct fans and register fans will pull the heated/cooled air where you want.

Have checked the ducts for dampers? They're often installed where the duct branches. It's not unusual to find they're not balanced well or the locking screws have loosened allowing the dampers to move on their own.

always good to have zoning, either via small separate heat pump or with a retrofit like AirZone (not sure if something similar is available there) which modulates the flow to each duct from the air handler.

How much electricity was the fan using? :)

Indeed, sounds like a problem with the fan. My 3000sf house uses 1100W for the fan, and about 4000W for the heat pump. I expect converting to mini-splits would increase, not decrease my overall power usage.

700W for the gas ducted heater fan. That’s the steady state energy consumption of all 3 units heat pumps running simultaneously. This is a small house of 100 square metres/1100 square feet.

Obviously a new EC fan will be more efficient than a 20 year old AC fan, but I’m talking about a retrofit application here.

Pretty sure mini splits are significantly more efficient today, with SCOP of above 5, so that seems unlikely?

I recently replaced my [central, ducted] heat pump, and the new one is rated with a 4.981 SCOP. It's fairly efficient, but not the most efficient on the market.

-40% for the duct heat loss

That seems kind of high for insulated ducts, where does that number com from?

US energy.gov

It would be nice to actually link the source[1] (PDF).

The stat is that you lose between 25-40% efficiency for "typical" existing installations. The document goes on to explain that an insulated duct which doesn't leak doesn't have this kind of efficiency loss.

[1] https://www.google.com/url?q=https://www1.eere.energy.gov/bu...

This unit runs at about 5

> Ducts are dead.

Ducts are still needed to circulate air, especially if you want to remove stale air (e.g., bathrooms, kitchen) and bring in (filtered) fresh air (to bedrooms).

Not being snarky but why don't you just open the window for that?

I have a CO2 detector that I believe is a reasonable proxy for stale air. When it goes above 1000 I simply open the windows. By the time I remember to close the windows the reading is almost always below 500.

On the west coasts of Canada (BC) we've had insane forest fires the past few years and you 100% want to filter the internal air when it's extremely unhealthy outside. We're talking air quality index in the 300+ range or off the charts at times. Plus, we've had these heat domes were it's in the high 30+ and just gross inside, where you really want to open the windows, but you're letting in tons of pollution. Basically, you need to cool off and filter the air at the same time.

[1] https://www.airnow.gov/aqi/aqi-basics/

I have a routine for this scenario: open the windows in the morning for 1-2 hours, then close everything and clean the air internally (I have a 24/7 sensor running and know when the air is good or bad).

That seemed like the easiest thing to do without making much more complicated system. Basically risk 1hour of bad air for 23h of "clean" air.

This. We live <50’ from an expressway, so after air sealing and replacing all of our ducts, I added a MERV 16 filter to our air handler. We had the windows open at night a few years back (no ac as well), and I woke up to smell of smoke from a forest fire after the winds changed direction. AQI2.5 was 200+ inside. Closed windows, ran the fan on high and after a couple minutes the AQI throughout the house was within healthy range (tested multiple locations). Unfortunately our furnace model leaves few realistic options for controlling it programmatically, so I still have to manually turn on the fan when AQI drops.

Where I live, it can get very cold. Not always very efficient to open windows for 5 months out of the year.

A great option for keeping CO2 levels down in a house is with an HRV (or ERV) [1] that will heat the fresh air coming in to cycle it throughout the house.

[1] https://en.wikipedia.org/wiki/Heat_recovery_ventilation

There is an open source 3D printable unit design here which I installed in my window and works well for relatively efficiently exhausting the CO2 from one person in cold weather: https://www.openerv.org (license: CC BY-NC-SA 3.0)

I did not 3D print mine, but ordered it, though as an early adopter, adjustment was required.

Do you know, is there a document explaining the design somewhere? I can see from the Google images some of the parts, but not clearly all the parts nor the flowpaths and such.

From the ERV/HRV (Energy Recovery Ventilation / Heat Recovery Ventilation) wikipedia page: https://en.wikipedia.org/wiki/Energy_recovery_ventilation#Ty... :

> During the warmer seasons, an ERV system pre-cools and dehumidifies; During cooler seasons the system humidifies and pre-heats.[1] An ERV system helps HVAC design meet ventilation and energy standards (e.g., ASHRAE), improves indoor air quality and reduces total HVAC equipment capacity, thereby reducing energy consumption.

> ERV systems enable an HVAC system to maintain a 40-50% indoor relative humidity, essentially in all conditions. ERV's must use power for a blower to overcome the pressure drop in the system, hence incurring a slight energy demand.

In Jan 2023, the ERV wikipedia article has a 'Table of Energy recovery devices by Types of transfer supported': Total and Sensible :

> [ Total & Sensible transfer: Rotary enthalpy wheel, Fixed Plate ]

> [ Sensible transfer only: Heat pipe, Run around coil, Thermosiphon, Twin Towers ]

Latent heat: https://en.wikipedia.org/wiki/Latent_heat :

> In contrast to latent heat, sensible heat is energy transferred as heat, with a resultant temperature change in a body.

Sensible heat: https://en.wikipedia.org/wiki/Sensible_heat

There's a broader Category:Energy_recovery page which includes heat pumps and thus mini-splits: https://en.wikipedia.org/wiki/Category:Energy_recovery

IME you don't use an ERV alone. You'd use it _with_ a Heat Pump. The ERV is all about transferring heat from one airstream to another. It's _not_ a device that manages indoor temperatures though, just recovers some of the latent energy in the air. In the process it's also managing humidity mainly as a by-product. The humidification properties of the ERV allow you to run the Heat Pump in a more efficient manner. I have an HVAC geek friend who explained the whole process, but essentially (in non physics/fluid dynamics[?] terminology), if the Heat Pump doesn't need to dehumidify air it can operate more efficiently.

Not to be snarky, but if the weather outdoors is uncomfortable enough to be using climate control, why would I want to open the window?

Because presumably in this case you would want to open a window for fresh air, and simultaneously run your heating system to heat up that fresh air?

I was respond to a comment that presupposes the need for fresh air. If you don't need that, feel free to close the windows then.

Airborne allergens can be an issue, and dust more generally.

Seems like it would be more efficient to wear a climate controlled bubble suit than heating up entire rooms. And you could even go outside when it is cold or hot or dusty.

You do realize that “open the window and hear that air” is massively energy inefficient, right?

I don't know; is it more energy inefficient than having a fresh air intake via a duct? Maybe they are comparable in the absence of a heat recovery ventilation system (mentioned by a sibling comment upthread)?

You don't necessarily need to take in fresh air to freshen air in certain ways. It might suffice to pass it though a good filter.

HEPA and carbon filters do wonders for cooking smells, particulates etc, but unfortunately do nothing for the main reason you want air exchange with outside, which is CO2 buildup.

Our house has a heat exchanger that exchanges air. So the outgoing air changes the temperature of the incoming air.

You want to open windows in opposite sides of the house to quickly circulate air from outside to inside. 5 minutes should be enough. It will get colder, but most of the heat is in walls and furnitures and as long as you only open the windows for a few minutes it should be quick to heat up the air again.

For the fresh air that this thread is about, regardless of whether it comes through a glazed window or a duct connected directly to AC system?

Because it smells bad inside? Because fresh air feels good? Not to be snarky, but how did you miss these use cases?

If it's pretty cold outside, then you're throwing all of the ostensible energy savings of a heat pump out the window the minute you open it to air out the house.

Following the thread of conversation, it just didn't compute to me:

>>>> Heat pumps are great for climate control >>> Yeah, ducts are dead >> What if you want to recirculate air in your house through your central air filter to eliminate smells? > Just open the window

It's like we've hit a contraction: the premise is that we care about energy but the contractions is then that we don't and we open the window while climate controlling the house. So to me it does seem to prove that in some climates, duct work with a central blower and filter mat not be dead.

For an existing dwelling, the best solution is probably mini splits (wall mounted) combined with decentralised heat recovery ventilation as required.

Ducts running in an insulated space are sources of huge energy loss.

*uninsulated

Yes correct! Thank you!

I think there's a middle ground.

We've just today had our first snow of the season here in a lower elevation of the Sierra Foothills. It's been chilly for 3 months or so, and our heating is an 'old school' ducted propane furnace. In time, we'll replace it with a heat pump, but not this year. Anyway, we're sensitive to accumulated odors that go with a well insulated, closed-up home in winter.

Every evening, we open three doors in the house to the outside. This is after the furnace has entered its timed 'off for the night' state. We exchange pretty much all of our air for fresh ambient, which is great when we wake up in the morning.

The impact from doing this on our propane bill is undetectable. This is because air, even humid air, has a trivial heat capacity compared to the warm house structure and contents. Those are by far the greatest energy reservoir in our home. Very little energy is lost in a daily air exchange with the ambient.

*edited for typo

I'm not sure why "Heat pumps are great for climate control" went to "ducts are dead".

I live in Florida, we've used Heat Pumps for as long as I can remember. We also have central air handlers with blowers and ducts to distribute the conditioned air. Mini-splits can _also_ be ducted mini-splits. According to my HVAC geek friend, mini-splits are pretty terrible about humidity control (an important thing in Florida). For proper humidity control you'd ideally have a dedicated set of dehumidification ducts (powered by a central dehumidifier) as well. Mix in an ERV and you have the ability to build a fairly air-tight house with _controlled_ ventilation and very efficient conditioning of the air in the house.

The Melbourne climate I was referring to needs heating 9 months of the year. The vast majority of houses have very simple, inefficient gas ducted heating. Rightly or wrongly, humidity control is generally not well considered.

I was going to install an ERV system but the payback was not within the life of the equipment.

Someday I’ll build a Passivhaus with a system as you describe.

No doubt: majority of the southern US went to heatpumps with central air handlers 2-3 decades ago. Ducts are definitely not dead. Or, if they're dead, then they must be as dead as BSD. :-P

A ventilation system allows you to filter (not a luxury when you live in a big city, where you will be breathing pollutants otherwise) or perform some thermal magic if the outside air is very cold (or very warm), by running the outflow and inflow pipes really close to each other.

Which CO2 detector do you have?

The one recommended by SwiftOnSecurity years ago. https://twitter.com/swiftonsecurity/status/12230876092216115...

Part of it is code. Make-up air systems need a duct for example. Also a lot of people like their air filtered so opening a window isn’t great for that. Also winter.

I used to have a bathroom without an extractor and in the winter with the window open the cold air would just cool the walls and cause more condensation there than I’d get with it closed.

On cold days you should open not the windows longer than 5-10 minutes at a time for exactly that reason.

I have a bathroom without an extractor. If I don't open the window the mirror fogs up in seconds of turning the shower on, and over time I get mould. If I do open the window it stays clear the entire time. By the time I'm out and dry the moist air has left and I close the window.

This morning it was -5C, so not cold by continental standards, but certainly cold enough.

In the UK recirculating air is very rare. In cases that bathrooms don't have a window (or indeed in new houses where they do) there's an extractor fan, but that just vents the air directly outside.

Allergies, humidity, heat, cold, rain, noise, privacy, and the hassle of doing it manually.

digression: Any recommendations for a good CO2 detector?

TFA Dostmann AirCO2ntrol Mini is a relatively cheap one that works well.

AutoPilot APCEM2

The only requirement is "2 channel low drift NDIR gas sensor". Cheap CO2 detectors either have zero IR sensors (instead they guesstimate eCO2 using a VOC sensor) or a single IR sensor that requires weekly calibration outdoors or it will just assume that the lowest sensor reading means 400ppm.

They're obviously no replacement for exhaust fans in bathrooms and kitchens, but there's a number of ductless energy recovery ventilators that can give you fresh air in your bedroom(s).

https://www.buildwithrise.com/stories/ductless-heat-recovery

Thank you - this could solve a problem in my house. We had CO2 build up in our bedrooms and the only way I have found to ameliorate the problem is to have our HVAC fan running continuously at night to circulate the air in our house.

Agree, ducts are wonderful! If you don't have ducts, go ductless for sure.

I paid real money to have my ducts removed. They cause issues installing comprehensive insulation and caused hot/cold spots on the ceiling.

Honest question: Why would one care about cold or hot spots on the ceiling? I don't spend much time up there.

It’s still a thermal path between inside and outside, and thus wastes energy if you’re trying to maintain an internal temperature that is different from the external temperature. Also there are radiative effects - hot spots on ceiling will radiate IR into your space. Just try standing under a corrugated steel roof in the summer.

Approximately 70% of the heat loss from your body is as radiated heat. Ceiling insulation is critical for thermal comfort. Have a look at the Efficiency Matrix YouTube channel videos on insulation consistency.

The average temperature sure. But would uneven spots have that much effect on the thermal radiation I get sitting over a meter away?

Less that 2% of insulation being out of place can waste something like 40% or some ridiculous amount of energy. It's quite nuts how even just a little break in insulation can have a significantly negative effect. A few years after I moved into my first home - a townhouse - I added some R-16 bats to the already existing R-12 insulation in the attic and it more than cut my heating bill in half. It was a three story narrow, townhouse - not that much square footage of ceiling compared to the walls/rest of the house but it made ALL the difference. If I didn't live it, I wouldn't have believed it. And I kind of did it on a whim since I didn't need that many and Lowes was having a sale on insulation. I would have done it the first week I moved in and had a couple far more comfortable winters!

Okay but that's not what I was asking. That much heat loss will affect the overall temperature.

He did answer what you asked, but I think you may be losing sight of the forest for the trees here. Maybe re-phrasing will help?

They explained how something could cause uneven spots and low average, as far as I can tell. Because those spots leak so much.

But I want to know if there is a way uneven spots could cause a problem without some effect tanking the average. What do uneven spots themselves do?

The uneven spots may indicate the presence of leaks. The leaks can have an effect on the average temperature.

Hot air rises and thus heat escapes through the ceiling if there's spots that aren't well insulated.

Because in the winter the thermal energy within your room will “flow” out of those “cold spots” at surprisingly high rates; in summer those spots act as space heaters. In both scenarios they will adversely affect the ambient temp of the room. In short, whatever method you use to heat/cool the room will have to work harder and will take longer. Here’s [0] a good overview of heat flow in this context, with some hints towards the math behind if you wish to go deeper.

[edit: add link]

[0] https://www.energyvanguard.com/blog/Flat-or-Lumpy-How-Would-...

I might be totally misled, but I think of it as a parallel resister circuit. One area of low resistance is extremely significant.

Am I crazy, or are those two sentences completely contradictory?

I think he means having a duct work for the whole house for a central heat pump is good. But having a heat pump per zone is also good if you don't have ducts for the whole house. Some newer home designs separate heating and cooling from the air exchange systems so there are multiple zones of heating and cooling.

I thought it was a joke. If you don't have ducts, you are by definition ductless. So that's how you must go.

> So that's how you must go.

No, you can go to ducts by installing them. I believe the comment is advising against doing so.

I read it as: Ducts are better but not so much that it's worth tearing everything apart to install them. If you don't already have ducts, you should definitely use a ductless system. If you do have them, you get some other benefits.

Ducts are great with a heat pump and an air handler with variable fan speed.

A recirculating central heating system doesn't do that. As mentioned below you either need exhaust only ventilation, balanced ventilation or ideally ERV/HRV. All of the above are available in both ducted and ductless forms.

>Ducts are still needed to circulate air

>A recirculating central heating system doesn't do that.

They definitely circulate air, and they definitely filter the air. Whether there is fresh air depends, mostly no.

Good callout. Some people have the strangest reasons to hate high-efficiency ductless systems.

Except it's incorrect. The best system is a "ducted ductless" system that circulates and filters air throughout the house.

I've seen that terminology used on US websites, it took me a while to get my head around. In Australia it would just be called ducted reverse cycle. In the vast majority of cases it would be "ducted ductless" I guess: outside unit connects via refrigerant lines to a heat exchanger and fan in the roof cavity, when then distributes the heated/cooled air to rooms via conventional ducting.

Nobody calls it that, it would just be called a ducted heat pump. The refrigerant lines just run to a central air handler where the ducts start in the house, instead of the air handlers that mount on the walls.

How do you go ductless in a 6000 sq ft home?

Two multi-head units should work just fine.

If it's an existing build with ducts, stick with that. If it's a new build, then like the other poster said, you add more units. See the top of any commercial building for example: heat pumps all over the place.

Another option is to supplement an existing ducted system with a ductless one adding additional zones where you might want conditioning over night. E.g. bedrooms where you want to sleep in cold A/C in the summer where the rest of the house can warm up a bit, or a person in the household who likes their room to be warmer than everyone elses in the winter.

A recirculation system will prevent high levels of CO2 buildup in occupied rooms, particularly with closed doors. I've measured the difference in our bedroom overnight between having the fan on and off, and it was dramatic (if I recall correctly, something like 700ppm in the morning vs 2000). Even if it's only keeping the level consistent throughout the house, that would be a benefit. But every house will have some amount of air leakage as well; a recirculation fan with a fresh air intake (which all modern ones have) will pull in fresh, filtered and conditioned air to replace air that leaks out. If that's not sufficient for indoor air quality, then you can crack a window or set an exhaust fan to run periodically. I haven't generally found that necessary though.

ERV/HRV has its place it less moderate climates where there is significant efficiency loss from pulling in outdoor air, especially if indoor conditions require a significant amount of fresh air turnover. But a central HVAC system with a recirculation fan most definitely can be beneficial in a lot of cases.

It’s worth noting that ASHRAE ventilation standards are based on “bioeffluence” levels which may or may not correlate well to other IAQ values like CO2, VOCs, etc.

In have ducted mini split units in my home, made by Mitsubishi I designed the system to work with merv 13-16 filters. I can run the fans and filter my air as well as use the units for heat and cooling. I installed fresh air intakes on the return units that can pull external air when they are opened.

It's really a very good proposition. Has all of the advantages of central heating and the efficiencies the heat pumps

> Ducts are dead.

How do you move the heated/cooled air into/around the house without ducts?

It’s a ‘mini split’ in US lingo. There are thin, highly insulated refrigerant lines going between the outside unit and the inside unit. The inside unit exchanges heat with the air. https://www.daikin.com.au/our-product-range/split-system-air...

That thing's an eyesore compared to a duct to me.

Much like solar panels on the roof (which I have also heard Americans describe as an eyesore), once they are common enough your eyes just slide over them and you don’t notice.

I don’t see rooftop solar panels unless I go outside and intentionally look for them.

A mini-split system puts an ugly, cheap, plastic wall-cyst within your field of view in every room they’re installed.

Why are they plastic wall-cystst though? Wouldn't a manufacturer offering a less obtrusive look (I'm not thinking of fancy boutique, just Ikea grade surfaces) alongside a standard interface for third party options get a huge market advantage?

> your eyes just slide over them and you don’t notice.

Nah.

There have been minisplits in the US for years, they are just not very common. Moreover they have been commonplace in Asia for decades now. They are noticeable. I personally think they look like ass. They are huge and you are blind if you don't notice them. There is a reason why ducted or recessed models are available internationally for luxury homes. It has nothing to do with Americans.

They're noisy too. Not loud, it's a quiet hum, but it's annoying if that annoys you, some people are sensitive to noise. The system I have doesn't seem to have a variable-output control, so it uses an on/off hysteresis that drives me up the wall. I could deal with a constant hum, but the stop start every minute or two is annoying. A previous house I lived in the ducts were absolutely silent unless it was on high you could hear some airflow noise. They can be placed anywhere wall floor ceiling (depending on construction of course), and have a wide range of styles.

Ducts are a superior look and experience IMO, just slightly less efficient. Nothing wrong with preferring them.

They’re not even less efficient if installed correctly, it just takes some thought and some insulation. And you get really good filtering with very low likelihood of mold in the bargain.

Though mini split heads can be ducted too. There are several choices, wall heads, ceiling heads, ducted heads etc. The wall head is just the cheapest solution since it’s very easy to install.

Just to add to what the other commentator said, ducted based systems are VERY hard to balance. It is possible using something called an Volume Damper, but it is uncommon (and adjusting them can be challenging, sometimes requiring removal of drywall).

So people COMMONLY wind up with unbalanced floors, and people typically try to fix it by adjusting the vent register opening with mixed success.

Part of the problem is that the thermostat is biased to wherever it is located. You can get systems with remote add-on temperature sensors, but that doesn't by itself adjust where heat/cold is being sent through a ducted system.

The great thing about a Mini-Split is that you're, at minimum, heating each floor independently with its own thermostat. You can then put in e.g. interior door vents that simply let air pass between common areas and the rooms when the doors are closed.

This can go even further with for example two Air Handlers per floor (quad units) on the east and west. So that as the sun moves, the correct level of adjustment can be applied to only the side of the floor that needs it.

I moved from a ducted heating house to a multi head split system house about 18 months ago.

One of the biggest pros (in addition to the improved efficiency of a heat pump) is I heat and cool less space than i did before because i can target individual rooms. When i'm in my office all day I only need to heat my office. When it's hot and I'm struggling to sleep only cool my bedroom. There's no point in heating my living room^^ at 08:30 in the morning if i don't intend to spend time in there till 17:00.

Sure, when it gets to 17:00 my living area might not be comfortable, but that can easily be overcome by turning it on half an hour or so beforehand (either manually or with a timer).

^^ I don't live somewhere where freezing pipes are a concern. But i'd imagine you could just set them differently, slightly above freezing for the rooms you aren't in and a comfortable living temperature in the room you're in.

How would it behave in a place like Chicago where we've had recent weather events that take the temperature from 40F to -10F in a couple of days? Will the system catch up that fast without ducts?

Faster since you just target the rooms you occupy.

Since this is the top comment right now, what is integration with Home Assistant/Hubitat like?

I don't think the hardware is that expensive in the US, it's the installation (which costs more than the hardware).

And mistakes by installers will cost even more. Our installers didn't flare a line set connection properly and it leaked slowly and that was a very expensive bill (especially since refrigerants have changed so much).

Our Daikin indoor units have also had condensate leaking issues, probably due to poor installation.

Ductless heat pumps do seem like the future but I think there are issues with regards to condensate draining, air filtering, and indoor unit cleaning/maintenance and replacement that could be done much better.

Daikon is way worse than Mitsubishi from what my hvac guy tells me

Mitsubishi Electric or Mitsubishi Heavy Industries?

I sourced opinions far and wide and in the end it seemed to be a coin toss between Mitsubishi Electric and Daikin. A lot of it comes done to parts availability, and both seem very strong in Australia.

I live in a cold climate

Mitsubishi is gold standard in cold climates. It’ll pull heat from -30F air.

There's no reason that's unique to Misubishi. My parents Fujitsu has done so.

Both brands trade off as best cold weather heat pumps in ratings/evaluations (quick Google search should confirm), they’re both fairly high quality versus competitor brands.

Dealer salespeople are loyal to their brands and shit talk the other brands, so I'd take that with a grain of salt. I own both brands, they are basically the same.

>And mistakes by installers will cost even more.

I once looked at a house with a new GSHP horizontal loop installed in the desert southwest US. I talked to the installer and they said the loop was only 12” deep. There’s no way the ground maintains steady temp at that depth, meaning you’re losing efficiency in the hot months when you need it most. Not to mention thermal pollution which will exacerbate the problem and the risk of hitting the loop with even minor ground work. They were adamant it was a good design.

Unfortunately, many installers jump on the bandwagon without the necessary expertise.

Twelve inches? If that's true it seems like it would get ruined quickly by roots, animals, vehicles, lawn mowers, and basically everything else.

Yeah, I know it seems more likely that was a typo, but that's what they told me :) Tbf, roots, animals, and mowers probably aren't that big of an issue because it was mostly xeriscaped desert.

I take your point, but installation faults in central gas heating are also very common, but perhaps less obvious. The main one I’m thinking about is poor sealing or placement of the return duct, causing entrainment of air from the wall cavity. Source: local experts, and then I inspected my friend’s houses (hah).

I love our Daikin mini-splits (came with the house), but as you allude to I've had to become an mini expert on deep cleaning them. They've can get GROSS with mold when used for cooling, and the cursory filter only does so much. That being said, now they stay clean for a few years after a deep cleaning -- though my first few attempt before I refined the process did not stay clean nearly as long. (Proper water pressure and disinfect is key.)

Cleaning basically involves a dedicated cover + drain that diverts water to a bucket, and blasting it with what's effectively a "low power pressure washer" I can use indoors (carefully), and "Lemocide" to properly disinfect... And coil cleaner for the fins. Takes me a good 4+ hours per unit, largely spent preparing the area in case there is any rogue spray. (Though TBH I may be a bit obsessive about getting it right.)

I also had a drain leak as you mentioned -- blasting the drain line with aforementioned "low pressure washer" helped with that. Still a bit gross to deal with. (And learning how to properly disassemble and clean the drip tray is the final thing I've put off leaning for a completely-thorough deep clean... I'm a bit horrified anticipating what I'll find...)

The no 1 reason I bought the Daikin model referenced over the comparable Mitsubishi Electric is that it has the ‘MOULD PROOF’ function. It runs the fan automatically after you have had it in cooling mode, to evaporate the moisture build up from the interior condenser coil, thereby removing the moisture required for the growth of bacteria and mould.

So far, it seems to be working! Better than relying on everyone to manually do it (literally this is the instruction in the Mitsubishi Electric user manual).

If you live in any kind of area with high humidity you just shifted the mold from the AC unit to the rest of your house. Hell even here in the desert I'm not sure I'd want to use that "feature".

I live in the desert. Any humidity we can get in the summer is good.

We are talking about the tiny amount of water vapour left on the interior condenser. The idea is to bring that back up to room temperature so that it doesn’t stay there near the dew point. The total amount of water inside the house does not change!

It only becomes mold by sitting and growing. If the A/C dries it after use, it doesn't have any time to grow.

Yes, over time - any amount of moisture will produce some mold. But it will be negligible.

Where does mold even get the energy to grow, it really seems to spring up from nothing but water.

The surface of our planet is so rich in bio material that some tiny amount of mold can be found in almost all unfiltered air. Instead of trying to eliminate all of it, home builders focus on preventing it from growing. Indoors, mold often has everything it needs to grow except standing moisture, so it's important for everything to either dry out or circulate water.

The fins in the heat exchanger will get covered in dust and dandruff over time. This provides a reasonable media for the mold to grow on.

That definitely helps and I used to do that in my car where the A/C got smelly pretty quickly. Just run the "fan" for a few minutes after you turn off the A/C and it doesn't get gross.

But one problem is the dust in the house. It will collect on the unit and hold moisture and give a great substrate for mold to grow. But regular cleaning usually takes care of that.

We also had a drainage problem after ours were installed. We were very fortunate that another, more experienced tech from the same company came by to follow up on a different issue and took it on themselves to inspect the drain line. It would have leaked into our wall for a long time before it became apparent something was wrong. These units (ours are also Daikin) are a dream to operate but you definitely need to triple-check the drainage on first run.

I'd love to see a youtube video of your cleaning methodology.

Most of the videos from HVAC people are... sketchy to the say the least.

I've seen videos where they dismantle the whole indoor unit and leave the coil just hanging from the line set or zip tied to the backplate while they take the fan and drain pan outside to clean.

One easy thing we've found that helps with drain clogs is to use a shop vacuum from outside to suck it out (using a towel/rag to get a good pressure seal). Takes around 5 minutes per drain per cooling season.

This is a video for the Mr. Cool brand of mini splits. Starting about the 45s mark you'll see how they do it without removing the unit. https://iwae.com/resources/videos/mrcool-care-kit-ductless-m...

I'll try recording something next time I clean one of the units (one needs a deep clean this spring); no promises though. In the meantime, here are some quick notes/resources.

This video shows a similar process using water pressure to clean the unit: https://www.youtube.com/watch?v=xcIVAv8YbPQ

Some more tips and modifications:

- I cover the electronics in a garage bag held with tape. No need to unscrew the black cover over the power wires to disassemble (I unnecessarily removed this a few times heh).

- I ended up really liking this cleaning shrowd after trying a few; the hard pieces on the sides are key for making it easy to secure nicely, which many others lack: https://www.amazon.com/gp/aw/d/B083S85X97

- I spend more time (like 30min+) spraying the blower wheel so it spins. I alternate spraying with fresh water with spraying diluted "Lemocide" (@10% dilution) from a spray bottle a bunch of times depending how dirty it is. I use this <https://snowjoe.com/products/sun-joe-wa24c-lte-24v-150-psi-m...> which at 100 PSI is 10x stronger than a hand pump sprayer, but 10x weaker than a real pressure washer. I.e. the sweet spot IMO.

- I use foaming coil clean from a can to clean the fins if they're particularly dirty. (WARNING: I have not used in the same cleaning as the Lemocide since I haven't confirmed if they're compatible, so be careful of any reactions if you use both in the same cleaning.)

- I take the outer casings outside for a quick rinse with the hose and dish soap if they're really dusty.

- I tape cheap plastic mirrors at 45 degree angle above the unit so I can see it from above and carefully vacuum the back coil (there are 3 folded over in a U, and you can only see 2 from the front). Otherwise this just accumulates junk and is hard to see. This also really helps with finding the 3x clips at the top of the case that secure it to the back housing.

I may have a few more notes worth sharing at some point; feel free to ping me if you have any specific questions.

Edit: See also this quick video on unclogging the drain line on a Daikin (though I used the sprayer against the tube instead of my mouth...): https://m.youtube.com/watch?v=GDrHe-rli98

This is exactly the same setup I have here in Launceston.

Another great thing about having three seperate units is if one breaks, rare as it is, you're not stuck without heating / cooling.

I am leaning more to this solution for this reason. Trying to get any tradie quickly these days doesn't happen. Trying to get an aircon person in an Australian summer is worse.

I despair for the rental market right now. High prices and landlords are generally crap at amenities they don't personally use.

After a lifetime of renting terrible houses, I’m now in the position to be a landlord. I’m trying to be a better one.

I got a similar setup for my house as well. Being able to selectively cool rooms that are in use is great. However, I do wish the insulation was far better. Unfortunately I’ve noticed that Melbourne houses are usually very poorly constructed due to expensive raw materials and labour.

Have you examined your insulation with a thermal camera? Might be worth your while to get an energy inspector out. Personally I haven’t yet, mostly because I can still see low hanging fruit to fix.

Yea have some pretty obvious improvements pending as well. But that’s a good suggestion - might get someone to come give a professional assessment before I put in a 7kwh unit for another room.

You don't even need a pro - you can get FLIR cameras that attach to cell phones for around $100 and they are more than adequate to show you areas of irregularity and worthy of targeting. I got one years ago mainly as just something to play with but I use it ALL the time for all kinds of things. Having a thermal camera is crazy useful.

I have a cheap Uni-T thermal camera. It’s great fun!

Are you asking why the Daikin Alira X is more expensive in the US? It's because it's not a brand that is normally found here.

If you went with a common US brand you can get a good system with 4 units and a 36,000 BTU heat pump unit for around $6,500 USD installed.

I don't love the wall units - they're pretty ugly, even the new ones. If you're getting a mini-split, the in-ceiling or wall cassettes that are hidden are really the way to go IMO.

Can you give me an example of a comparable model available in the US?

In the Australian market, the efficiency of the in ceiling or in wall units is lower than the high wall units. They are also much cheaper to buy and install.

Wow, really? Prices seem much higher than that in Seattle. A friend got 3 handlers totaling 24k BTU for like 12 grand.

That’s double the price I paid here!

Seems to just be Seattle tax, I had to get a water line replaced in my home and the quotes were $2-7k higher than I've seen suggested in other regions. Tradework here is inflated likely by the salaries of tech workers in the city.

In my locale, trades like plumbing (including gas & hvac), drywall, roofing etc range from 1 to 1.5 what contract developers from NTT, IBM et al are billed at. In absolute terms - 110 - 140 for contract devs and trades are often "to busy" at 170.

I got quoted 16 grand for the same 24k/3 zone system in the Seattle area by the guys who install thru COSTCO. I ordered the hardware myself for $4300, bought about $300 worth of tools, and installed it in one long weekend. It’s really not that difficult. Basic electric installation, some special technique and tools needed for the plumbing (University of Youtube can help), pressure test, pull vacuum, open the valves and enjoy.

https://www.ecomfort.com/Fujitsu-F3H24W07071200/p65952.html

I’ve been eyeing https://mrcooldiy.com/, even easier.

The problem with Mr. Cool is that their DIY claim is because you don't cut the lineset (I believe they give you 25 ft). Any excess length you're supposed to coil up and hide, which is not ideal- plus you'll lose efficiency.

Or you mount the condenser further is all.

I believe they now sell other size lines and extensions.

I got hung up on the excess line set idea and did a full DIY install of a non-DIY model mini-split. I bought, borrowed, and rented a lot of tools, spent a lot of time researching and learning. I really wish I went with the DIY model.

Despite that lesson, I may do it again when I finish my attic space, but this time I'll add copper line brazing to the list.

As long as the unit is pre-charged, DIY installs aren't that bad. I've done 2 Pioneers at my home. I spent around $150 in tools.

Awesome, I’ve been considering installing a few myself but am not sure if that’s silly or not.

I’m mostly curious how these DIY units compare to Mitsubishi, which seems to be what all the installers recommend.

How do you get the pipes through the wall in a pre charged unit? Do they have two pieces connected by a special valve? I’m curious about how they keep the air out of the lines.

Pre-charge has one of two meanings here. Most mini-split units have the refrigerant in the compressor unit. After a complete installation, evacuation, etc, you open a valve to release the refrigerant into the lines.

There are also DIY variants where a fixed line length comes from the factory with either a vacuum or a refrigerant in the line. The lines have metal seals on the fittings that are ruptured when torqued down on the equipment.

Was there anything beyond the extra time/effort that made you regret going with a non-DIY model? I’m considering doing the non-DIY in next year or so.

No, not at all. I enjoyed it but my wife had a different expectation of completion date than I. My advice is to get the tools, don't shortcut, so that you have confidence at each step.

Stuff I had already specific to HVAC:

-R-410a manifold, gauges, and hoses.

Stuff I went out and bought:

-Nitrogen tank pressure regulator and hose for HVAC.

-Mandrel pipe bender

-Flaring tool

-Micron vacuum gauge

-A slightly better copper pipe cutter and deburring tool.

Stuff I rented/borrowed:

-Vacuum pump from Autozone. Free. It was plenty big enough for a minisplit.

-Full nitrogen cylinder rental from Airgas.

Things I'm glad I did:

-Used a wall mount instead of a pad for the compressor unit. Unit stays clean.

- Pressure testing with nitrogen. It's worth the money and effort to know up front it doesn't leak.

-Followed a more thorough procedure for vacuuming/drying which involves vacuuming down several times and flushing with nitrogen. I got a much better vacuum after subsequent flushes.

Thanks for the follow up! I understand completely. Somehow my wife stuck with me after more than a few significant home projects with misaligned expectations around completion. Re: wall mounting vs pad. Do you find noise transmission to be a nuisance?

I was on the lookout for it, as it was a concern of mine. I haven't noticed an issue. It's also mounted on an exterior wall of my garage. That wall lacks insulation but has drywall. It may be more of an issue if it shared a wall with a bedroom. The mount has rubber dampeners between the unit and the arms.

This is the way. And don’t forget your refrigerant license, which is super easy/cheap to get. Some manufacturers will void your warranty if not installed by someone unlicensed.

> Ducts are dead

Great. You just eliminated approximately 15% of lazy screenwriter tropes for thrillers and action movies. Now they are forced to rely on replacing live surveillance camera feeds with a loop.

No one is crawling through house ducting

TELL THAT TO THE LAZY SCREENWRITERS

> In a house I own in Melbourne, Australia

Same, and we have just implemented 2 x 7.1kw units along with about 7kwh solar panels. Our heating costs have plummeted and we can survive on days like today (17th Jan) with minimal impact to our comfort.

We are looking at changing water heating next as this is now the biggest part of our utility usage.

It doesn't get that cold in most places in Australia does it?

Heat pumps need to be scaled for the maximum heating or cooling load, whichever is greater. The optimal situation is that the heating and cooling loads are similar, but in colder parts of the U.S. the heating load is much larger than the cooling load and the case for the heat pump is not so good as a place where the need for heating and cooling are more balanced.

Depends on your frame of reference but in Melbourne it can get to around 1 degree Celcius in winter (33~F). Sometimes subzero but very rarely

In upstate NY it gets a lot colder than that

https://en.wikipedia.org/wiki/Syracuse,_New_York#/media/File...

the average temperature is below freezing for four months.

That actually sounds like a perfect climate for it.

In my part of Texas, it gets below freezing on 12 days a year on average, but within the last two years it's been as low as 7F / -14C.

I guess that's the value of having a big heat sink, the Pacific Ocean, at your doorstep: temperatures are more stable.

We have a brand new Daikin VRV system in new york and are currently working on retrofitting a nat gas heating solution - heat pumps aren't a good fit for anywhere north of Atlanta:

When it's really cold out (say 25F or below), the heat pump stops for around 10mins to defrost the exterior coils, which means no heat running at all in that period, and this pause happens more frequently the colder it's outside. The end result, our ~1400 sq place took more than 24hrs to heat up from 55F to 72F when we got back after christmas.

Also you don't save any money on operating it, even with the efficiency yade yada the cost of electricity will run you more than the equivalent in nat gas. So nothing but downside.

In Melbourne’s climate where piped methane costs 1/3 per kWh that of electricity, but heat pumps are 300-500% efficient and you remove the duct loss, for most people their heating bill drops by 2/3. Add solar self consumption and you are way ahead.

My limited understanding of the defrost cycle is that it’s most a problem around 0c? If it’s a colder or warmer it doesn’t get triggered as often?

Regional Vic for me, Daikin Alira X's installed in rooms about a month or two ago, and they've been great. Very energy efficient, and individual units in each room means we can match everyone's preferred climate -- even heating one room while cooling another!

They're pretty quiet, too. You can certainly hear the air coming out, but it's fairly quiet and certainly wouldn't be noisy enough to bother you over tv, work, or anything else.

It’s going to take a lot of work to get Melbourne homes up to modern standards for heating cooling and insulation!

The problem I have with mini splits is that they are an architectural eyesore. Are there any high quality ones designed to be built into walls discretely like cove lighting has done for lighting?

There are floor mounted units that can be recessed into a wall. Alternatively, ceiling cassettes (not ducts) can be good. https://www.mitsubishielectric.com.au/wp-content/uploads/202...

How does it function on a day like today? My evaporative cooler works decently at this temperature but with the side effect of making the floorboards sticky

Ducts are good for indoor air quality though. Keeping our central fan on at low speed all the time significantly reduces measured CO2 in occupied rooms, particularly bedrooms overnight.

Which side of the city are you on, could you let me know who you had do the installation please?