First, a gas-fired power plant converts about 40% of thermal energy to electricity, discarding 60% to further heat the planet. Then a few more percent are lost in transmission lines and voltage-lowering transformers. Only then that electricity is used to heat water or air in one's house.
If you just directly burn that same gas in the house to produce heat, it's nearly 3x as efficient.
The best coal plants can archive 47% efficiency, https://www.brighthubengineering.com/power-plants/72369-comp...
I only mentioned the gas-fired power station to make it an apples-to-apples comparison. It would be hard to compare e.g. to solar panels, even though direct hearing by concentrated sunlight might be feasible.
It's worth it for a larger volume though. Not so much for a small flat.
A typical solution is recirculating the water so that it stays hot.
(I have a gas tank heater and the faucets far away take a bit to warm up, because of the water in the pipes)
I bought a used Wemo plug for $10 and set it to only be on for 3 hours in the morning and 3 hours at night. Now we have hot water at any of the times when we actually would want it, and we aren't wasting money/energy to keep hot water on tap 24/7.
The problem is using devices that are either timed or (even worse) just runs 24/7.
Ideally you'd want one that runs on demand when triggered by a switch: hit the button, it runs for 30-60s while you undress, and then we you turn on (e.g.) the shower the water is already hot.
The hot water supply for the shower should be the same as the sink, and so when you go to shave or brush your teeth, that's then already primed as well.
Do a search for "Gary Klein", who has written a lot of designing good hot water systems over the years.
And they cool the air around them, so if you live in a hot area they save more.
In this same remodel I also convinced them to get heat pump / AC combo unit to replace the old gas furnace. Again amazingly cheap (even compared to gas), but also higher upfront cost.
This is in a coastal California region, so I'm not sure how well these heat pump solutions will work in colder places (ice would likely form on the heat pump near freezing, limiting its capability), but if anyone is looking to upgrade either a hot water heater or an AC unit, I cannot recommend the heat pump option enough (if you can get through the higher up front cost).
The worst case is efficiency approaches resistance heating at 1.0, maybe with backup resistance heat strips. But a well designed system to match worst case load should rarely see this.
For some reason they've really only been widely available in the US in the past few years.
Well actually it'll see it quite often. Every time a heat pump goes into defrost mode it'll use resistive heating inside to hold over while it's working like a traditional air conditioner to thaw out the outdoor coils.
I think it's cheap energy. In places like Japan they've been using heat pumps a long time
To make the installs cheap, these systems use flare fittings that almost all seem to leak. Couple that with the fact the 412a systems run at high pressure and you get a lot of leaking refrigerant.
No HVAC techs I’ve met like the 412a systems and most seem to be hoping for more sanity from r32, though that will have its own set of problems (flammability)
Also, if you are worried about the refrigerant leaking, you can sacrifice a little bit of efficiency and buy a unit using CO2 as a refrigerant with a GWP of you know: 1.
I think the biggest problem here for leakage are random construction dudes cutting the pipes when they demolish or remodel homes. If only they could gather the gas in the outdoor unit before, all of it would be saved.
There is no excess indoor heat in winter in 99.9%+ non-passivhaus homes.
(They would however de-humudify the space they are in, but that's another thing...)
I'd argue that every house that has any sort of ventilation, even naturally aspirated ones, have excess heat in that any amount of air leaving the house "unreclaimed" while there is any heating need contains wasted energy.
Heatpumps using that energy are very prevalent in the Nordics and Scandinavia, even with a majority of the time being heating season here.
Refrigerant leaks are still an issue though, but moving to hydrocarbons and CO2 will mitigate that. Even R32 is a step up in that regard.