The plumber recommended not using hot water from the boiler, since it takes so long for the hot water to start coming through it wasn’t worth it.

I have a hot water recirculator for this. The price I pay is that instead of waiting for hot water at the kitchen sink I've to wait for cold water, as the hot water is recirculated through the cold water pipes.

I have seen a return loop on the hot side, but not returning through the cold side. Do you have more info on this? (I do wonder if recirculating hot through a pipe next to a cold pipe would result in heating the cold)

The thing consists of a) a pump that goes on the output of the water heater, and b) wax-based valves that go between the hot and the cold under each sink where you want hot water without having to wait a long time. The valves turn on when the water on the hot side cools, and they close when it gets hot. The pump stops when the valves and hot faucets are all closed, and it has a timer for scheduling hours of operation. I believe it's this:

  https://aurorixs.shop/product/watts-500800-instant-water-recirculating-pump-system-with-built-in-timer

That sounds like a great way to get Legionnaire's, unless I'm missing something.

I've been doing it for 15 years. No legionella here.

I think all apartment buildings have recirculators so somehow it works.

actually its quite the opposite. because the hot water is constantly recirculating its hard for the bacteria to grow. Kind of like why they say never drink from stagnant water but water that is flowing is safer (not neccessarily safe to be clear)

So you’re always pumping hot water through your pipes? Does that not end up wasting quite a bit of energy? I guess in winter it’s not a big problem since you’re heating your house anyway, but presumably in summer it is just adding unwanted heat?

In the winter, as you note, it's not much of a waste, and it helps keep the pipes from freezing.

In the summer... this is central Texas, so the sun helps keep the water in the pipes hot, so I imagine that the pump is on less often than in the winter. I've not checked though. My gas bills are not out of the ordinary, so I think it's not a ridiculous waste.

4 day old post but these can have timers so they only run for one time window such as when you wake up.

I have to ask, showers?

It is unsurprising that it varies by country, etc. Below is pure speculation while eating a snack:

Likely dishwashers for the NZ market are designed to actually spend sufficient time heating the water.

My impression from watching the TC videos a while ago is that at least in the US, (many) dishwashers probably only do a insufficient time interval of adding more heat to the water.

It makes sense that different markets developed different ways; the brands that optimize for the local trends (cold vs hot water) can skimp on some features and have lower costs.

Yes - over the last decade or so they removed the heating element in most US dishwashers. So they either are connected to the hot water line, or have a mechanism to heat the water (or both).

I could be wrong but I'm pretty sure that even today almost all US dishwashers have some mechanism to heat the water, just maybe not the giant exposed element in the bottom like older ones. Water out of the tap is going to be on the low end of usable dish-washing temps at the very beginning of a cycle, let alone 45+ minutes later.

The reason cold or luke-warm water is a problem is that the programs are extremely simple and just assume the input is 110-120f and won't stall the cycle for waiting for the target temp.

I forgot about the exposed element. These days most plastic spatulas withstand high temperature. Back in the day I think every North American family had at least one yellow spatula destroyed by the element.

My dishwasher doesn't have a big exposed heating element in the pan but it still has a water heater to it. It still gets the water very hot even if I start it without getting the hot water flowing first.

Is it still possible to plumb hot water into such dishwashers? Then the heating element have less work...

I bet some manufacturers don't even use temperature sensors in many models, and just assume an approximate incoming water temperature, and heat for a fixed time period according to calculations on amount of water in the system. This guess comes from the impression that cheap temperature sensing circuitry isn't the most reliable long-term.

If true, that is a recipe for a lawsuit if it went wrong.

How did you conclude that they aren't the most reliable long-term?

Temperature sensing is extremely simple and cheap. Bi-metal contacts have been used since the dawn of electronics, and the solid state versions are also really simple. (Making components that are temperature invariant is the hard task.)

Fair question! My speculation here comes from thermistors being relatively common replacement parts. (clothes dryers, ovens) As you mentioned, temperature-invariant is tricky, and I think it's often a non-linear but close-enough for the design. I have the impression a failure mode can be if the temperature-response behavior changes over time.

A bi-metal contact is only good for a single temperature, I think? (can be adjustable like thermostats) (I'm sure many but not all dish-washers probably do only need a single temperature...)

I bet you're wrong. Is there a website where we can make an adjudicated bet JUST against each other. How many dishwashers come without a hot-wash option? Any dishwasher that didn't heat water enough would struggle with hard fats.

My dishwasher has a scalding 75°C option.

> Are modern US dishwashers plumbed into hot water?

Yes.