Water heater is actually one of the hardest hashrate heating products to solve. I'm eager to follow https://www.superheat.xyz adoption.

Challenge is that it's a closed volume. What we call a "closed loop". Can only add so much heat to it. Like stuffing more luggage into a mini van. The more full it gets, the harder it is to pack the next bag. Same with the water heater. The hotter it gets, the harder it is to dump more heat into it.

In this way, the miner needs to throttle down and lower it's heat output as the tank starts to accept less and less heat.

And water heater tanks are insulated. They store the heat until you need it.

Long story short - you need a relatively small miner that can run for longer, or a powerful miner that runs in short bursts. Either way, not that many sats will be stacked in the grand scheme of things compared to a home heating system like a furnace or boiler - constantly dumping heat into the home as the home loses heat to the cold environment outside