# Wood stove hot water coil?



## farminghandyman

Any one use a hot water coil in there wood stove for heating water?

what are your experiences, with it,? 

does it over heat the water often? 

are you on a pressure or gravity feed water system?

do you have a tempering valve on the system? (valve that mixes cold to the hot water if it is extra hot),

would you do it again?


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## Ed Norman

I tried it heating seed beds in a greenhouse. I would not make any type of closed system with it, only a gravity fed open container so no pressure could ever build up. You could make a batch system and draw water from it when needed, but you could also put a kettle on top of the stove just as easy.

I'm thinking of doing it again when we remodel the greenhouse. Uh oh, I have a plan..


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## woodsy

I put a coil on top of my Ashley woodstove last fall, had a recessed area on top enough for about 30' x 3/8" coil, worked some sand in around it and covered it all with a metal plate. runs on the same circulator pump as the solar water system.
It's a open loop (non pressurized) that runs through the same 150 gal non pressurized heat exchange tank as the solar drain back system. 
With this volume of water there isn't much worry about overheating. I had both the solar and woodstove loops running this morning. Temp in the heat exchange tank is around 115* now.
Basically, the woodstove loop helps keep the water preheated on cloudy cold days before entering the electric water heater. 
No tempering valves here
No pressure relief valves except on the elec. water heater.
When introducing water into the hot woodstove coil i do it slowly so that the water "burps" softly instead of forcefully. This woodstove loop is operated manually 
whereas the solar loop is auto.
I like it , it helps and was easy to set up since i already had the solar system tank to tap into.
The solar side of the system cranks out more hot water than that little wood stove coil does though, when the sun is shining.
I can raise the temp of 150 gals about 4 degrees per hour on the wood stove coil when the stove is running hot..


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## SolarGary

Hi,
Some info and stories on coils in wood stoves here:
http://www.builditsolar.com/Projects/BioFuel/biofuels.htm#FireboxCoils

I've read through the booklet from Lehman's that's listed at the link above, and it looks good to me.

You really want to be careful about the safety aspects -- you can get serious explosions if you don't. You want to be really careful about not installing shutoff valves that can end up isolating the coil with pres/temp relief valve.

Gary


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## farminghandyman

First of all thank you for all who have responded so far,

I am well aware of the safety issues on hot water systems.

This will be a open system and vented to the out side, and will use T&p safety valves any way, 

the storage tank is or will be 50 gallons, (using a used 50 gallon electric hot water heater for the storage tank, NO other power or elements) just wood heat, the coil I wanting to use is about a 20" U similar to the http://www.hilkoil.com/product.htm product, made out of black pipe 3/4" I do have a 30 gallon I could use as well, 

The water will be pumped out of the storage tank via a pitcher pump (on the floor above). The hot water storage tank will be fed by a fresh water reservoir near to the hot water storage tank that is above it. the water will be used for domestic hot water. a drain back solar hot water panel may be added for summer time use. 

one of the concerns I have is over heating the water, and if a tempering valve would be need or suggested, and if it would work with out being on a pressurized system.


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## ET1 SS

We have a 50' length of copper tubing in the upper chamber of our woodstove. It heats the water that flows through our radiant floor system.


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## greg273

I have 50' of 1/2 copper tubing wrapped around the flue of my woodstove, and this is connected to a 50gallon water tank, it works by thermosiphon. This is plumbed in to the rest of the house plumbing, and it definitely needs to go thru a tempering valve first! With a good fire going, it probably heats about 15 gallons of water per hour. I have a thermometer and pressure gauge (as well as the mandatory TP relief valve) installed and I've never seen the pressure rise much over the ambient system pressure (about 45 psi). Been in operation for two full winters now, going into the third and I love it. Makes it much easier to justify nice long hot showers when you know its recovered heat your using!


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## farminghandyman

besides a tempering valve for the water line use,

I will be adding a thermostatic controlled heat dump so if it get above 160F in the tank, it will start to cool the water via a water to air heat exchanger that will work on a thermo siphon principles, 

yes T&P valves will be used as well for a final safety system that if it gets above 210, it open and dump water to cool it, one in the tank and one near the heat coil, the shut off valves, to the heat coil will have automatic drain back on the exchanger side so it can not trap water in the coil, 

and this is not a sealed/pressurized system it will be vented to the atmosphere, 

~~~~~~~~~~~~

I could not find a thermostatically controlled heat dump valve, 
so I have made a small manifold that that Will use a automotive thermostat that will open to circulate the water if needed,


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## greg273

farminghandyman said:


> besides a tempering valve for the water line use,
> 
> I will be adding a thermostatic controlled heat dump so if it get above 160F in the tank, it will start to cool the water via a water to air heat exchanger that will work on a thermo siphon principles,
> 
> yes T&P valves will be used as well for a final safety system that if it gets above 210, it open and dump water to cool it, one in the tank and one near the heat coil, the shut off valves, to the heat coil will have automatic drain back on the exchanger side so it can not trap water in the coil,
> 
> and this is not a sealed/pressurized system it will be vented to the atmosphere,
> 
> ~~~~~~~~~~~~
> 
> I could not find a thermostatically controlled heat dump valve,
> so I have made a small manifold that that Will use a automotive thermostat that will open to circulate the water if needed,


 Those are pretty nifty coils...if I went to that type of coil, my only concern would be placement, that is placing them where they wont get a big old log thrown into it. (since they are inside the firebox) My wood furnace had a coil that came with it just like those, but the previous owner (my dad) found he was regularly overheating the water, not surprising, since I dont think he used a tempering valve, so he got rid of it. 
I've been pleased with the performance of the copper coil...it heats up pretty quick. I probably didnt need 50', that takes up about 18" of flue pipe, probably could have gotten by with 25', but i had an extra coil laying around and used it.


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## greg273

ET1 SS said:


> We have a 50' length of copper tubing in the upper chamber of our woodstove. It heats the water that flows through our radiant floor system.


 you've had that setup for awhile, as I remember... hows it working out? Just curious how many feet of radiant tubing are you heating in the slab?


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## ET1 SS

greg273 said:


> you've had that setup for awhile, as I remember... hows it working out? Just curious how many feet of radiant tubing are you heating in the slab?


Sorry I missed this previously.

It seems to work great 

We have 600' of radiant tubing in the floor. Just a wood floor, no slab.


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## dirtman

I have three steel pipe grids in by wood heater. Two feed the downstairs radiant pex in a concrete slab and one the thin concrete slabs on the second floor. One feeds a storage tank made from a hundred lb propane tank and the the double to a large oxygen bottle. I leave the system open to the atmosphere but even with the tanks closed it has never built up more than 50 psi and that was with a roaring fire. I started out with a mixing valve but took in out because the floor soak up so much heat that the system never overheats but I leave the circulating pumps running whenever the fire is in the box. I'm always a little concerned with what would happen with a power outage so when we get one I don't use the heater. I have a wood stove in another part of the house and we just hunker down there. I feed pex lines directly out of the tanks and even with occasional 200 degree water the exposed sections of pex have had no problems. If I were feeding directly into the system without the tanks I would probably need the mixing valves.


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## MichaelK!

For my own woodstove I was thinking of buying this 18S Hilkoil kit.
http://www.hilkoil.com/product.htm 

It includes everything including the pressure relief valve. Just have to add pipe and a tank.

Anyone here have experience with this company?


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## ET1 SS

MichaelK! said:


> For my own woodstove I was thinking of buying this 18S Hilkoil kit.
> http://www.hilkoil.com/product.htm
> 
> It includes everything including the pressure relief valve. Just have to add pipe and a tank.
> 
> Anyone here have experience with this company?


Those look nice 

I have no experience with them though.

I used 50 foot of 3/4" copper tubing in our woodstove, for heating water.


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## jwal10

We have a small stainless steel coil in our wood cook stove firebox. There is a small pressure tank with 2 pressure relief valves. It is on our gravity fed spring waterline, with a pressure reducer/backflow valve set at 15 lbs pressure. It is more of a warm water system as the wood cook stove has a small fire box, limiting the heat output. It is plumbed to a kitchen sink, bathroom sink and the shower, all very low flow, no mixing valve....James


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## MichaelK!

ET1 SS said:


> I used 50 foot of 3/4" copper tubing in our woodstove, for heating water.


Can you give me some clues as to how much hot water and how long it takes to heat it? Suppose for example I start a fire in the stove at 5pm to cook dinner, and keep it going till well after. How many gallons do you think I could heat and how hot will it actually get over what time period?

IE: suppose I plumb a 30 gallon recycled water tank. How long to heat it to 140F?


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## ET1 SS

MichaelK! said:


> Can you give me some clues as to how much hot water and how long it takes to heat it? Suppose for example I start a fire in the stove at 5pm to cook dinner, and keep it going till well after. How many gallons do you think I could heat and how hot will it actually get over what time period?
> 
> IE: suppose I plumb a 30 gallon recycled water tank. How long to heat it to 140F?


Our heated-water circulates into a 200-gallon thermal-bank. Heat is stored there. Our radiant-floor-loop circulates that water out through our
radiant-floor-loop [which includes all of our home flooring and a heated towel/clothing rack].

I have seen that if I slow down the flow enough, the output will be steam. Increase the flow a bit and I would have seriously hot water.

But mostly we leave it circulating at full speed with the thermal-bank. [A taco-7 circ pump which is the most commonly used home-heating system circ pump; mass-produced, carried by every plumber, most readily available and the cheapest]

Usually water coming out of the stove compared to going in, is about 15degrees warmer. [but that is with full flow. The water is moving fast, slow the flow and the temperature differential would be hotter]

Overall temp changes as time goes on, obviously as the thermal-bank warms-up. Which is also directly effected by whether or not our radiant-floor-loop is on, or not.

When our radiant-floor-loop is running, the temp of the thermal-bank climbs real slow. Maybe 10 degrees an hour. But even that is effected by how much fire we have. If you really get it going, then it heats the thermal-bank faster.



If you fed a hot-tub of 200 gallons and nothing else. Starting at 5pm, I bet that by 10pm the hot tub would be fairly hot and steamy.



If you had a small tank, like 30 gallons, I imagine that in an hour you would have hot water. Maybe 90-minutes.


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## Mattie420

I was wondering the same question, kinda. I have an electric water heater. Could I tie in a pipe that use pre-existing holes on the water tank and run them, to say, the back of the stove? In a grid pattern? or in a coil around the stovepipe? What kind of piping, copper?


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## Mattie420

Wow ok, sorry everybody I just saw all these posts before my last post. I saw that kit a couple posts above and that answered pretty much all of my questions, and I think I'm going to order that kit and report back to let everyone know how if works!


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