Converting my Stove into a Water-Heater

[Nick Cole]

I live in upstate New York.  Not everyone is lucky enough to live in rural America.  This is a suggestion for those who do.

I have two stoves I use with varying regularity for heat.  In the basement is my corn pellet stove.  My wood stove is in the living room.

Until last year, the only purpose for these stoves was to heat the house.  Then I found a website, www.hilkoil.com, offering a new kind of water-heater.  Instead of using oil or gas or electricity, it uses the heat from a stove.  Any kind of stove.  I decided to install the water-heater in my woodstove, since that's the one I use the most.  

They call it a "Thermo-Bilt Coil", and it's a loop of stainless steel.  It actually mounts inside the stove.  I just cut two holes in the side, near the stovetop, with the hole-saw bit included in the kit.  I think the whole kit cost me less than $150.  If you're not the handy type, your regular handiman should also have an easy time installing it.  Thermo-Bilt provides a good set of instructions (which are written in the U.S.A.)!  

This doesn't mean I am abandoning my regular water heater.  When I'm not using the stove, I just turn on the circuit breaker for my hot water tank.  If instead I use my woodstove, the hot water goes straight from there, into the regular (turned off, electric) hot water tank.   

The stainless steel coil heats my water to the same hot temp as my electric tank.  It easily paid for itself the first winter.  Now, for six months out of the year, I can stop paying the electric company for all my hot water.

-NickCole

[Norm]

Yes....60 years ago in our hand fired coal furnace

we put exactly the same in our furnace just black

pipe in the holes provided and connected to a hot

water uninsulated tank.

  Also had connected to the tank a small stove

with a dome hot water jacket for heating water

to wash clothes in the summer.....little tank of

used motor oil dripped on some ashes to run it.

 

[strider3700]

I have been thinking of building my own system like this but I was concerned about the possibility of the water sitting in the pipes when not in use then turning to steam and exploding.    What prevents this system from doing the same?

[behoof]

HI Nick,

A couple of years ago I posted a Diary entry right along the line of your post. Just thought I'd resurect it and share it with you.

http://www.fieldlines.com/story/2006/1/14/3919/61705

Your's is a great post and very interesting , thanks

[jonas302]

this NEW water heater was invented right after fire was

The only control you have is the temp and pressure relief on the existing water heater it should let water out at about 165 i don't think it is ever an issue we have been using domestic coils for thirty years or so in woodstoves and a oil heater  

[GaryGary]

Hi,

I think there is a potential issue with steam explosions as described here:

http://www.woodheat.org/dhw/dhw.htm

I think you just have to be very careful how you do the plumbing.

Steam explosions are ugly.

Gary

[Boss]

I too have been wanting to build a water heating system for our wood heater. My plan which I haven't implemented, is to have a small 12 volt water pump to circulate water to our existing floor heating pipes. The possibility of a failure is alway present though. Dan from otherpower told us that the steam engine and boiler isn't something to be trifled with, He never leaves it running without watching it. Good advice

 

[jacobs]

Agreed! At one time we were using our combination cookstove, which has a water jacket in the firebox for thermosyphoning water to a water heater, for heating our water. I had previously installed a couple of valves inline so I could shut off the water if needed. I don't remember why but I shut off both valves to the firebox and forgot to reopen them later when built a fire. Thank goodness for soldered copper pipes....the solder melted and blew the pipe apart. It really made a mess but there was little damage except for having to repaint the wall behind the stove. If I had used steel pipe, there could have been serious injuries.

[Drives]

From the woodheat.org link

"The first thing that needs to be said is that a wood stove is not the right device for heating water for in-floor radiant. You would never get enough heat off a wood stove to make a dent in radiant heating needs."

I guess I better tell my wood stove that it just "thinks" it heats my radiant in- floor heat.

All kidding aside, the statement above is baloney.  I have heated 2000 square feet of house in upstate NY with a stainless steel hot water coil in my wood stove for the past 14 years.

It works well down to zero degrees outside, then you need to really stoke the fire to keep up with negative temps.  

http://www.thermocontrolheating.com/model400.htm

http://www.nationalstoveworks.com/hotwater.htm

I have the 400 model, and wish I had the 500.  The links are to the same company, and if you look close....the parts list has the same coils as Nick's linked website.  It must be all related some how...even the area code on the phone numbers are the same.

Hope this helps.

[spinningmagnets]

When I was a hydraulic mechanic, I did a lot of work with 1/2" stainless steel tubing (outside diameter, called "dash eight", for 8/16ths of an inch). We had benders that would give it a gentle 90 degree turn without kinking. Just for laughs one night we found that with some fiddling, we could get a "U-turn". Then, by skewing the input angle, we could form a continuous up-rising coil about 6" in diameter.

I have also read about filling tubing of several types with salt or sand (to prevent kinking), then hand-bending them around a drum or pipe, A large stout pipe can be adapted to become a leverage bar.

The raw tube was about 10 foot long. With the two ends outside the chimney, it would be fair-sized heat exchanger with no joints inside the chimney.

It was common tubing, rated for 3,000 PSI continuous, and 4,500 PSI burst.

Every major city should have a hydraulic shop in the phone book, just some options...

P.S. Use a relief valve, it can even bleed to the outside ground. In case the valve ever fails shut, have an easy to reach short section of soft pipe that will split in a safe part of the loop, and also not flood the house.

[Scott S]

Hey Guys -

I am trying to put together a similar project this summer.  A brief description follows - please give me any input you feel would help.

The plan in a nut-shell:

Currently we have a new construction ranch style house (6" walls) with a oil fired, forced hot water boiler.  My wife would like to have a woodstove in our livingroom for not only the appearence (she wants the glass in the door) but also to help with the ever rising cost of oil (pre-buy is already at $2.99/gal for next year).  My concern is that the livingroom will be 100 degrees and the bedrooms will still be 50.  I'm trying to think of a solution to transfer the heat in a single story, long house - so far I've come up with the following:

Obtain a large woodstove with built-in outer sheet metal shrouds that are now common on the newer style woodstoves (we've got a Napolean at our camp that might be a good candidate - here's a link to see the stove I'm referring to http://www.napoleonfireplaces.com/Webshare/wood/wood%20stoves/1900.html).

Remove the shrouds on the stove and construct two "coils" of sorts out of 1/2" copper on both sides of the stove and then reinstall the shrouds (hopefully you will not even tell the modification was done without a close inspection).  Connect both coils back into the existing boiler resembling just another zone on the boiler - with the understanding that this zone really works backwards - it brings heat into the boiler instead of carrying heat away from it to the baseboards.

Use an air conditioning thermostat near the woodstove to activate the circulator on the woodstove zone so that when the T-stat senses the heat from the stove it will automatically start circulating the water (heat) in the woodstove zone from the stove back into the bolier and, in turn, out to existing baseboards on whatever zone is calling for heat.  When we don't use the woodstove - the boiler senses that the temperature is getting too low inside the block and heats up the regular way using the oil burner.

Benefits:

Nice looking woodstove that can be appreciated visually.  Any heat that is not absorbed by the coils will be directly dispersed into the livingroom.  It uses the existing forced hot water system to distribute heat to the other end of the house.  Saves oil. Relatively simple to install.  Relatively safe since the boiler already has several expansion valves for safety.  The coils would be on the outside of the stove which would not tend to overheat and would not draw down the internal temp of the stove causing condensation and creosote issues.  Automatic back-up with the oil burner.

Problems (all guesses on my part):

Disimmilar metals (copper and steel) touching between the stove shrouds and possibly corroding?  Not enough heat transfer to the coils to even make a dent at heating the boiler?  Other issues I'm not seeing?

Thanks, in advance, for any help you guys have to offer,

Scott