Wood Water heater

[Blackfoot]

Hello, I was wondering if anyone has or knows of a good way to build a small wood heated, water heater. I seen one a long time ago where you built the fire in the bottom, the tank set on top, and the smoke went up through the center of the tank. the tank was built around the stove pipe. It worked real slick. but it was years ago that I seen this, and I can't remember just how it was built. The folks that had this unit used it for everything, and it did not take up much space. It was about the size of a upright 50 gallon water heater.
I would apreciate any ideas,,, thank you, BF

 

[srjones]

If it was me, I'd find an old gas water heater where the valves/thermostat/burner was shot, but the tank itself was still good. Mount that on top of an old wood stove and with some creative welding and riveting you might just have something.

 

[RonMar]

They make small wood fired ones for heating hot tubs...

 

[MikeD74T]

I have an 80 gallon electric water heater that is plumbed to my camp wood stove for cold weather use (just use the electricity in warmer months). I used a spring bender to make a 7" diameter coil of 1/2" od copper tubing that surrounds the 6" stovepipe. I used 50' of tubing which is about 25 turns. The coil sits on the stove as the stovepipe exits the stovetop. It is connected to a tee at the bottom drain & a tee at the hot water outlet & circulates by gravity heating the entire 80 gallons when the stove is running. I put a bucket under the relief as it will occasionally lift if no hot water is being used in really cold weather (-30F or colder) & the stove is really cranking. It provides 100% of our hot water if loads like laundry & showers are spaced out.
Previously, on top of another wood stove I had a 40 gallon short gas hotwater heater tank that was plumbed to preheat water going to my gas hot water heater. It didn't circulate as it was just in series & the relief lifted too often.
Either way one must be a little cautious as these methods have no controls to limit water temperature. MikeD74T

 

[scott_vt]

Mornin Blackfoot,
My Uncle Dave has an old woodstove that he ran a series of loops in the back side of the stove, using HD black pipe and circulates that into a stone lines tank. I believe he also has a pressure relief valve off of that tank with a catch bucket. I could ask him any questions if you have any specific questions about the system !

 

[AltavistaLawn]

A good friend of mine made one. Actually out of a 275 gallon oil tank..he put the fire box into the center of it, with a chamber in the rear to collect smoke, which has a removable door to clean it out.

They are usuall set about 100 feet from the home, the water lines are insulated and buried..the heated water is pumped through an "A-Core" mounted piggy back on your existing furnace, so that the fan blows the heat through your ducts. The water heater is controlled by its own thermostat to ct the pump and fan on when it gets too cold in your house. The heater has an "Aquastat" , usually set around 160 degrees to cut on a small fan on th edoor of the heater to draft the fire to get it hotter.

The two big down falls to it are: you have to walk to it and put wood in it, and clean out the ashes every now and then...and also they smoke a lot, because it burns cool compared to a regular heater and chimney.

They are the most efficient form of heat out there, followed by gas.

I may build one next fall.

 

[mjarrels]

I have the water heater option on my Harmon coal stove... just a large u shape SS pipe inserted into the firebox... just never hooked it up to a water heater. Previous stove owner used it and never ran out of hot water.

mark

 

[ditzel]

check out centralboiler.com there are a couple other companies that also make them. just google wood fired boilers. I was thinking of getting one a few years ago, but my neighbors are too close and the boilers put out a lot of smoke on start-up.

 

[patrick_g]

For DIY with a water heater conversion you need a gas fired water heater. Open up the bottom of the heater and mount the heater suspended so that the stack gasses of the wood fire pass through the water heater and on out of the space as before. Wood fire stack gases are more corrosive than those of propane or natural gas so you need to monitor the condition of the rig frequently. you need a pressure relief because with no thermostat and little hot water consumption it is easy to overheat the tank. It is possible to run a second path for the stack gases in parallel to the water heater and reduce heating by adjusting a damper in the bypass to reduce heating of the tank.

It may be beyond your intent but there are electrically controlled dampers that could be controlled by the thermostat on the tank and thus the temp of the water.

I would have some concern regarding the integrity of the water tank's heat exchanger. They will sometimes crack open when used normally with gas as fuel (can let CO into the room.) The stress of a wood fire and its chemically active stack gases might increase the danger of a leak in the heat exchanger which could introduce stack gases into the room where the stove is. IF yo go for a DIY solution be sure to install a carbon monoxide warning sensor in that room. They are pretty cheap insurance against waking up dead.

Pat

 

[pat32rf]

The commercial wood fired furnaces that we have up here have a simple loop of 3/4" pipe that runs thru the firebox. These are used as a preheat for a normal water heater via a gravity feed system. Great if you are heating a house with hot air at the same time. There are also wood fired boilers that are dedicated to heating hot water for hydronic systems. These have more coils and try not to heat any more air than necessary (waste heat). You can build one using any firebox and a steel pipe coil. Just remember to vent your relief valve outside where the steam from an overheat won't do any harm.
If you have a leaky heat exchanger with these systems you wind up with water in your fire, not CO in your house. You should also have a temp sensing valve that will control the max temp of your tap water. The larger the storage tank the better. There is a lot of physics involved to make it both safe and efficient....Your "average" residential plumber won't have a clue if my experience is any indication.