Preheat water before electric water heater

[spikchik69]

The house I bought this summer has an electric water heater that accounts for half of my monthly electric bill.

Now that the colder weather is here (at least in the north) I have been using the wood stove in the basement. Its not really a "stove" like the one my grandparents cooked on, it is about 4 feet high and is designed soley to produce heat. The wood stove sits about 4 feets from the electric water heater.

I know nothing about plumbing, but I have an idea that I would like to bounce off you guys.

Since the air directly over the wood stove is hot, why don't I hang a metal water tank off the floor joists directly over the wood stove, and insert this tank into the cold water infeed line for the water heater. The copper cold water infeed is located directly over the stove.

I would have to work out some details like size (20 gallons?) and type of metal (I was thinking copper?) and where one would even find a tank like this, but before I started off on a wild goose chase or call my local plumber, I just wanted to know if this is even feasible.

Even when the stove isn't on, I think it would still save money if the frigid well water were to rise even to room temperature.

I was thinking that there might be a problem if the water got too hot and started to turn into steam, and some sort of blow-off valve might be necessary, but the hot water heater itself has one, so maybe since they are connected, that one could work double-duty. I don't think the water would get that hot though.

Any advice would be greatly appreciated.

-Stephanie D.

[drd]

my immediate thoughts are on the weight of the tank and water hanging off your ceiling joists ...

You'd be better of using the exhaust gas from the wood burner in a heat exchanger unit to heat your water - what does the wood burner do at hte moment?

S

[e-mail] wrote:

[spikchik69]

Yeah I thought about the weight. 20 gallons of water would weigh roughly 160 pounds (right? 8 pounds per gallon?). I have seen my brother do chin-ups on a bar that was fastened to the floor joists, and he weights a lot more than 160, so I was thinking it should be safe. Plus the tank would probably be "attached" in 4 places rather than 2 like the chin-up bar, thus further reducing the weigh at each attachment point. Of course the tank weigh would have to be taken into account. I'm not sure how much a metal (copper?) 20-gallon tank would weigh.

The wood burner simply has a fan on the back of it to blow some heat off it. Recovery of heat from the exhaust is very poor, in my uneducated opinion. There is a 7 or 8 inch pipe that comes out the back. An elbow, a couple feet up pipe straigh up, then another elbow right into the brick chimney. I have thought about pointing a small fan right at that pipe. I know you don't want to cool things down too much because draw would suffer, but the chimney gets very hot as-is, so I don't think I could ever cool things down too much.

I have no idea how a heat exchanger works or how it would be implemented here. The pipe is very accessible so I'd be open to giving it a try. If it doens't work well, I could put the old pipe back in.

Thanks for the reply.. ..sd

[Jeff Wisnia]

You might be interested in looking at wood burning water heaters. AFAIK they mostly exist nowadays to heat hot tubs at campsites and other places where electricity or propane isn't available.

Way back when, it was not uncommon to have wood fueled kitchen stoves with domestic hot water heating capabilities built in.

Which reminds me, my first job back in the 50s was at a place that had developoed a gas fueled ammonia cycle refrigerator with an insulated domestic hot water tank on top of it. The water was warmed by the heat pumped out of the food storage part. The company trade named it "Stator". They made a prototype run of them shortly before WWII, but never took it to market.

Jeff

Jeffry Wisnia (W1BSV + Brass Rat '57 EE) "Rudeness is the weak man's imitation of strength."