Using woodstove to heat water

[weldingrodd]

Hi Folks

Hind Sight is always best!

I posted back in November on making a heat exchanger that mounted on outside of my woodstove. Was some question if it would heat well enough being outside but it did and worked well on a thermosyphon setup.

My problem was not spending the money for a new tank to cycle the water thru(did not want to commit my in use electric tank to this operation)and I put a used tank in to see if it would work ok. Of course "Murphy's Law" took over and tank leaked but not until I filled in driveway and let set for a week and it passed inspection! Then I mounted it in position for being hooked to stove and let it set with water filled and pressured up and still no leaks so I  hooked exchanger up and fired the stove and 8 hours latter nice warm water and 16 hours nice very very hot water.

So I made all conections to main house water system and as soon as I turned water on to added tank .......a major rupture under the tanks shell happened and leaked like a sieve!!!

Well I sure got a lot "I told you so"!!

Now I have to buy a new tank and start over again but at least this time I know its worth a new tank because it will more than make all the water we will use that is for sure.

I will post a few pics of the tank and exchanger as soon as Santa brings me a digital cam for Xmas...The one I dont know I am going to get!!

Merry Christmas All And A Happy New Year! Rodd

PS best part is I paid $10 for the used tank(guy said it was only a year old)(ha ha)

Now I have to drag it to landfill and pay $7.50 to dispose of it !! Oh well "ya get what you pay for"

[jtbartlett]

Hello Weldingrodd. Sounds like you are on your way with the preheater. What are you using for a heat exchanger on the stove? I would be interested in more details regarding your particular mechanics. I am starting on a similar project and deciding between baseboard heating elements (copper and aluminum) or a scrap radiator plumbed above the wood stove. Stove is currently located outside as well. Any information or pictures (!) would be appreciated. Good luck with the new tank.

Joel Bartlett

[BT Humble]

My problem was not spending the money for a new tank to cycle the water thru(did not want to commit my in use electric tank to this operation)and I put a used tank in to see if it would work ok. Of course "Murphy's Law" took over and tank leaked but not until I filled in driveway and let set for a week and it passed inspection! Then I mounted it in position for being hooked to stove and let it set with water filled and pressured up

"Pressured Up"?!

So far as I knew that's NOT how one does a wood-fired water heater.  Every one that I've ever seen is an open-to-the-atmosphere type with a float valve (usually in a separate tank) to control the water level, and an overflow pipe slightly higher than the float-valve level for when the water expands as it gets near boiling (and it WILL get near boiling!)

Please, please check with a plumber local to you to see if what you're doing is legal and/or conducive to a long and happy life.

With a pressurised electric or gas system the thermostat keeps the water temp below about 60C (140F), AND you have a pressure-release safety valve in addition.  If you're using a pressurised tank conencted to a woodstove you only have ONE safety device (the pressure-release valve), and do you REALLY want to be relying 100% on it to prevent your water tank from going boom?  

BTH

(aka Nervous Nelly)

[skravlinge]

The first tank get wrong, but the setup seems very  fine, 16 hours of hot on a fire.

Try to get a tank lasting 24 hours. You must do someting which can make  the eccess pressure or water to be disposed  in a precalculated place leaving the tank  in the same condition as it was.

[skravlinge]

Sorry I mean heat lasting for 24 hours .

[weldingrodd]

For my exchanger I used a 90' elbow into a 90' street elbow between 18" x 1" black iron pipe which gave me a multiple "U" shaped exchanger(serpentine) that runs along one side and the back of the stove. The cost was about $50.00 for everything. This was a lot easier for me to do than bend copper tubeing which would also work very well but being 1" pipe I figured it would give me a little more heating area so it would work a little faster to heat the water.

A friend of mine has a coil of 1/2" inside his woodstove and uses a pump to circulate...he thought mine would never heat the tank but much to his surprize and mine it worked very well.

Best part is mine needs no pump to circulate so one less thing to worry about if power goes out. Just have to make outlet of cold from tank is higher than lowest part of exchanger. Am told the higher the tank is the better also try to keep it as close to stove as possible.

As for the baseboard or radiator mounted on top of stove ..I know for a fact that baseboard will work well on top of stove as a friend in Maine did it years ago and fed water into his oilfired system into his zoned system and it worked like a champ!

He mounted it on top of a large cabinet type woodstove (Ashley) with tin side covers  and large slant finned top.If woodstove was fired, oil did not come on if vacant zones were shut off.

I still have one in my kitchen for days like today -4 at 5:30 pm in upstate NY and wind is gusting they say to 25 mph. Even a Penquin would be cold today!

If your outdoor stove has water you might only need a domestic water coil monted in water jacket to get water.

As for tank (first) it was used ..puchased form a shady looking guy at a garge sale/flea market type place. My sytem is using 20/40 pressure from my domestic well with deepwell pump. Max pressure is 40. I have a 210 degree/150lbs blow off monted in tank(auxillary) and same in my electric tank.

Reason tank went is was probaly 10 years old and had a leak already and just did not show till I got tank hot at 40 lbs pressure.

As soon as the Holidays are over I shall get a new tank and probably will be larger than the 40 gallon I had initally.  Rodd  Pics as soon as I get a cam.

Also typos do really show after you post dont they ...lol

[Drives]

http://www.cetsolar.com/ThermContrl.htm  This is what I use for radiant floor heating.  I bought it 10 years ago for $300 used.  I like it except it needs an ash pan...I'm lazy, and don't like to scoop out ashes.

[rotornuts]

Why not? The prv is the only device keeping most domestic tanks from going boom. Although considering it's hooked to a wood stove on second thought you may have a point. Perhaps a backup? As for legality - I'm sure the regulators wouldn't approve of many of the things we do here.

[weldingrodd]

Sounds like you like your stove also.

Mine is an ancient RiteWay which uses airflow similar to Thermo-Control. I am lucky I have an ashpan!!

I have to be looking for a new stove someday..probably sooner than latter...Will watch WantAddigest for a Thermo!

[PaulJ]

   A pressurised tank with an unregulated heat source (i.e. woodfire) is a definite no-no. Imagine the woodfire going full noise in the depths of winter, and no hot water being used at the time. The pressurised water could easily superheat to well above normal boiling point; at some point the pressure relief valve would pop open.

   When this happens, the tank pressure suddenly drops. The entire superheated contents of the tank could then flash to steam, expanding in volume 1700 times - kaboom! We're talking a serious explosion here.

   Be careful - Paul.

[troy]

Paul is right.

An uncontrolled heat source into a pressurized tank is a potential bomb.  When you get a steam explosion, it usually demolishes the entire building.  It is generally quoted that one gallon of superheated steam has the explosive potential of one stick of dynamite.  Ok, you're going 40 gallons or maybe bigger, so fifty sticks of dynamite with a twelve dollar insurance policy (temp/pres valve).  An atmospheric system wouldn't be too hard to rig up, which is inherently safer.

Having said all that, I'm the guy that's running a Lister cogen setup that's also an unregulated heat source with not one, but two, converted gas water heaters. So I'm breaking the law just like you are.  At the very least, I'd run redundant pop off valves, which is what I have.  I also keep a very close eye on my water temps, which have never gone above 135F.  The coolant loop of the heat exchanger only holds 3 gallons of non-tox antifreeze, and it stays reliably at 190F, but that part of the system is atmospheric, not pressurized.

Good luck, have fun, play safe!

troy

[Tippy]

I DO WORK DOWN IN CENTRAL MEXICO WITH THE RARAMURI INDIANS, AND THEY HAVE WOOD HOTWATER HEATS THAT WORK REALLY SIMPLY.  THEY USE OLD TANKS, (OLD PROPANE, ECT) TURN THEM VERTICALLY AND HAVE A FIRE IN THE BOTTOM, AND THE VENT PIPE GOES UP THROUGH THE REST OF THE TANK, THERE ARE FINS ON THE VENT PIPE TO HELP RADIATE THE HEAT INTO THE WATER. THE WATER SUPPLY COMES IN AT THE TOP AND IS PUSHED OUT NEAR THE BOTTOM.  ONE OF THESE SET UPS SUPPLIED ENOUGH WATER FOR 5 OF US TO HAVE NICE WARM SHOWERS. A VERSION OF THIS COULD BE BUILT ABOVE YOUR WOOD STOVE AND SERVE AS A VENT PIPE AND WATER HEATER AT THE SAME TIME.