There are a number of pilot projects currently in development to heat entire neighbourhoods using the waste heat from data centers.

Unless you've got a monster ML workstation under your desk or a crypto mining rig in your garage, that surplus heat isn't especially useful and isn't really worth harvesting. A typical desktop PC only dissipates a few tens of watts at idle or a few hundred watts under heavy gaming loads, versus many kilowatts for a typical domestic water heater.

https://www.gov.uk/government/news/thousands-of-homes-to-be-...

I have used a mini home-datacenter to heat my house in winter (very effectively - I used a fan to direct the heat towards the intake for the AC system and ran the AC fan). But I decided against the HW heater version of it from a cost recovery perspective - we just don't use that much hot water and we had a then-new high efficiency gas hot water heater.

However, there's a fairly straightforward way to get halfway there: You can run a standard heat pump hot water heater and put the computers in the same room with it. The computers will heat the air, the heat pump hot water heater will cool the air. Won't be as efficient as a closed loop system directly connecting the computers to the HW heater but you also won't need to worry about whether the heat production and consumption are balanced.

I’ve long been annoyed in the summer every time I turn on a heat generating appliance (stove, dryer, on-demand hot water) and then think about all the waste heat my air conditioner dumped out the side of the house in the last X hours. It would be amazing to somehow store that heat in a reservoir where it could be later used.

I doubt the extra piping and infrastructure is anywhere near worth it, but I sometimes fantasize about an experimental building that was designed from the get-go with a single integrated heat loop that all the major appliances were plugged into, and how that might look. Seems like the sort of thing that could be tried in a much more confined space such as for an off-grid RV.

The main problems I see are that we don't clean the insides of computer parts and we can drink water with way more calcium in it than is good for high temperature water heaters. Cooling water needs to be treated to not grow algae and bacteria in it, and a lot of times that renders it poisonous to drink. Conversely, drinking water has a lot of minerals still in it and those minerals will deposit and form scale on the insides of your heat transfer surfaces, which will severely impact performance over time. It may not even take that long depending on how hot the surface is and how hard your water is.

Two issues I see here would be that a) the demand and production of how water and compute power might not align and b) the amount of water heated this way would probably not be nearly enough for most people.

What is probably more feasible is to save on heating costs by heating your apartment partially with your computer.

Heat pump water heaters are a product you can (probably) buy today. They suck ambient heat from the air and stuff it into the water.

I really want to get one and pipe all the exhaust from my homelab to it.

Linus (tech talks) uses it to heat his pool.

Not sure if this is what you mean but an actual heat pump with a compressor could handle this— after all, an air conditioner cools your house to 23C by dumping the waste heat to an environment that can be 40C or more.

Kicking myself for not thinking of this... it's genius