For 10 years minus some months I’ve only had hot water heating on my woodstove (not a cookstove, just a heating stove) for hot water. In the summer I heat it on my electric stove. Hub has promised for a long time to rig something up. He’s getting close, going to wrap copper pipe around the stove pipe and store the hot water in an old hot water heater on the second floor, and it will run gravity to the bathroom and hopefully kitchen.
He’s researched some other do it yourself hot water heaters, my favorite besides a solar one, is the method of getting an old hot water heater, welding it onto a large truck tire rim (or maybe car tire would work), making a small fire box, and heating it that way. Of course pipes coming and going have to be engineered into it. He found a good website he’s going to follow directions from. That will be for summer hot water. We have so many trees we don’t have an area near the house with hours of sunlight.
He put an ad on Craigslist for non working hot water heater tanks, he got 5 I think. Umm, just realized Craigslist deleted the ad for some reason so we put it in the local paper. He got the tanks for free.
The ole sears woodstoves had water heaters built into them.
Check out Engineer 775 on Youtube. He was on the first Doomsday Preppers. He’s all about redundancy.