Heating water on wood stove

[weldingrodd]

I am toying with the idea of adding a 1 " black iron pipe heat exchanger to the inside of my very large Riteway wood Stove. But am afraid that after several hours and wood has turned to a huge pile of hot coals my water will become to hot and boil in the 40 gallon tank I have rigged to preheat the water for my newely installed  40 gallon water heater....(Thermo Syphon system)(cold water will force preheated water to new tank) So I am thinking of mounting a exchanger made from hot water baseboard with aluminum finns to capture the heat and heat the water inside the copper pipes. This will instead be mounted on the outside of the stove(side and backside) where I am hoping it will not get nearly as hot as it would if mounted inside the firebox where it would be much hotter.

I generally fill the stove in the AM when I leave and early evening and late night. Stoves gets the hottest after its wood is turned to coals.

I am gong to route the blow off protection piping outdoors on a down slope so It wont freeze in pipe.

Anyone tried this baseboard style to heat water on the outside of stove? I saw a fellow in Maine who used the baseboard to heat boiler water on top of a cabinet type wood stove with good results. Any ideas or thoughts greatly appreciated

[nothing to lose]

I use the flue pipe to gain heat sometimes. If you have an exposed metal pipe like mine perhaps run the heat exchanger along that. Heat going up the stack is waisted anyway so you might as well reclaim as much as you can. Running the baseboard heat exchangers vertically against that pipe should work well as the cold water will be at the bottom and rise through the tubing as it's heated. Your taking heat from the exhaust pipe not the room.

If you can't do that, then I think along the back or side should work well also. But then your taking heat from the room.

If you wanted to use the iron pipe inside the wood burner, just use less pipe for less heat. Depending how your setup is made, just run 1 foot of pipe inside where the heat is at. I've done that with fireplaces, just run in and back out and adjust the pipe inside larger or smaller as needed till I get the correct amount of hot water for the type fires I build.

[picmacmillan]

when we go moose hunting in northern ontario we use a gas tank(new of course) from generous motors coorporation i mean general motors....anyhow, there is an open mouth at the top of the tank to put more water in when needed and it also gives off a little steam which puts some moisture back into the air because the wood heat is very dry....if i could suggest one thing is to use maybe stainless steel as ordinary steel leaves the water rusty after its been used a while...it isn't very pleasant to look at when it is all rusty.......even if you were just going to use a small length of pipe as was suggested up top that stainless would be a good choice of material ...i don't believe the pipe would have to go inside the stove unless it was for an asthetic reason because i know that the outside of the stove pipe even 18" above the stove is about 800 degrees farenheit.....good luck...pickster

[dudevato]

This is a thread that I will keep an eye on.  I've been thinking of putting something like this together.  I've a woodstove that's in the house and happens to be not more than 10 feet from the waterheater that is in the garage.  I was thinking of a 'preheater tank', run from the stove in winter/solar in summer to take the chill off the city water before it enters my conventional waterheater.  A nice clean tank can be made from a stainless steel beer keg.  The large ones are about 12 gallons I believe. Just needs a few nipples welded on.  Looking forward to reading more.  

[jimovonz]

Fitting a 'wetback' to the inside of the firebox is very common here in New Zealand. You do not need to worry about the boiling of your water as long as your system is vented to the atmosphere (such a vent is mandatory here when using an uncontrolled heat source). I have never boiled my system but that is because I have a 500gal hot water tank (hydronic radiant floor heating). Such systems regularly boil the water in your standard size domestic hot water system. The water simply 'spits' out the vent on the roof. I'm sure you could capture a reasonable amount of heat utilizing an external heat exchanger, however I would say that you would get much more heat for less effort if you fit it internally.

[SDO]

Hello.

A little background, and maybe some questions that folks can answer.  I do

want to use solar, wind, stove heat and biodiesel for my energy needs.

I'm finishing up a 12'x16' two story (loft is 2nd) cabin.  Time for me

to consider the installation locations for said.  On the south side

of the cabin/house I'm planning on the front door (let the snow melt

off sooner), and also a 6-8' deep deck (haven't decided how much, but

leaning towards 8 foot) and a green house (got the 41 panes of older

glass for 7 bucks, yippie).  I want to put in a hottub/dummyload/heatlocker

that will take overload load from the 10' gennie I'm building (just started

on the blades, and going to build the DanB style 3 blade, dual rotor axial

system), along with taking heat going out the stack from the stove, and

also finally get some solar power from the sun in the greenhouse (the tub

is going to be in the greenhouse for moisture, relaxation, and also heat

that will keep the greenhouse warm during the winter months at night.

So, in all, does this sound pretty good, other ideas I'm missing out?

The stove is going to be just on the other side of the wall in the house

from the tub/greenhouse (south side of cabin), and I was also thinking

the gennie (likely to buy a FuKing or something in the future) would

be near that location also to tie into the electrical...  The panels

of the active solar system, will part (top panels) of the sloped portion

of the greenhouse (goes up 6 feet, and then leans into the house at about

32 degs off top dead center which is optimal at this latitude).

Hope I have done this right in design, and am very open to alteratives that

will save me wire, time, energy and money.

One concern, do I need to be concerned about overheating with 3-4 sources

of energy going into the tub  BTW, I'm going to be collecting and

filtering the roofwater...  My other thoughts are snow pack retention on

the roof.  I want a 12 over 12 pitch, and I know that is SUPER steep but

I need the headroom due to the loft having Thompson 2' footer walls

and the building being 12' wide and gables on this smaller end for hopefully

obvious reasons (south facing and also end where the entrance door).  Propanel

is too slippery and the L brackets I have heard don't do a good job unless

very heavy steel and big (3 inches off the roof surface)...  Should I do

regular shingles for snow pack retention and filter the water to get out any

petrolium products that run off with the water from said shingles, or propanel

and put heavy L brackets and pray the 12 over 12 isn't too steep?

Well, thanks, and good luck with your heatexchanger, I personally believe heat

going up the stack is one of the biggest losses and we can make much better

use of that energy.

SDO-aka-Todd

[kita]

one litttle quesion- doesn't transferring alot of the heat from the stove exhaust gasses via a heat exchanger run the risk of cooling them to the point of condensation? and then all the attendant hassles of low chimney draw and corrosive tar residues. asking mostly because I've wanted a heat exchanger for a while but couldn't square it with the expensive double walled insulated flue pipe I shelled out for!

Hoping this isn't even a problem but wanted to check... nice project with the cabin by the way. waiting for photos..

kita

[TrampArt]

Why not attach the greenhouse to the southside of the cabin, rather than a deck?  With a window it can help heat the cabin during the day, and the stove can help heat the greenhouse at night.  

[TrampArt]

Great idea on using a beer keg.  Make sure it's vented though, or you'll have a very large bomb.  Another "tank" idea:  Pick-up a non-working wet/dry shop vac and remove the stainless steel liner.

[TrampArt]

Coiling copper pipe around the stovepipe also works great.  

[ScottP]

Weldingrodd,

25 years ago I helped a friend set one of these up. We used a 10"X 14"X 2" stainless tank simply clamped to the side of a box stove. This tank made too much hot water. It was also too thin, we used 16 ga. (.060) material and ended up installing 5 3/8 pins through the thickness to hold 50 psi without bulging. We figured if we made another one 6"X 12"X 2" 1/8" thick it would be good. (mount vertically, 3/4 pipe couplings welded top and bottom)

We set up his electric water heater on a stand beside the stove so the drain valve was level with the SS tank bottom. Then pipe a drain valve, shut off and temp/pressure relief between them. You must use a temp/pressure in the heater loop if you have shut off valves to isolate it. (we did)

Coming out of the SS tank top pipe to a tee on the (hmmm I can't remember for sure but I think we used a tee on the hot water outlet of the electric heater) I'll see if my friend remembers and post back.

Any way where the top side of the thermal siphon attaches you will need a loop to form a heat trap (to help stop the heat transfer in your pipes)

Where your hot water exits to your house pipes an adjustable temperature mixing valve is needed, we learned this the hard way. The water was getting way too hot. These valves actually mix cold water with the hot to control the outgoing temp. At that time it was 20 dollars I believe, and well worth it.

Another thing we wished we would have done is mount a hinge and an adjustment bolt on our SS tank clamp. We just used an angle iron frame and welded 6 nuts to the stove to clamp the tank against it. A hinge and a screw clamp would allow the tank to be pulled away from the stove slightly to reduce output.

The biggest problems were encountered during sub zero weather when the stove was running at max. This unit was also in Maine.

Snap on thermometers made for copper pipe were a big plus too. It made for easy monitoring of how well the system performed. My friend used the system for 3 years before selling his house and never turned on the water heater during heating season (about 6 months here) The new owner loved it too.

If I was to make one today I think I would consider using a small circulator pump and a baseboard heater to use excess hot water. Set the start and stop temps to prevent boiling. If a mixing valve is used these could be fairly high. Utilize the heat in a room that needs it. Maybe your work shop

I think my friend has pictures, when I see him I'll ask and post them for you. Hope this helps.

Scott P

   

[weldingrodd]

What I am calling "heat exchanger is the piping installed outside of the stove. This would have no affect on the burn of the stove.

I think your talking about some that are designed to coil inside the stove pipe itself whick I guess do cause a problem  by cooling the smoke.

Read what Scott P posted and you can see what a simple tank mounted on the side of stove can actually do for very little money and with todays power rates you can save a bundle because I feel an electric water tank is one of if not the biggest user of power besides a dryer or electric heat we have in our homes.

[weldingrodd]

Hummmm......Funny you mention Maine.

That is where I first saw a fellow in Ashland Maine(minus 45 is not uncommon once in a while))Coldest place on earth I was ever at!!!)

A smarter person than I named Sherman Wea...(name protected!!)lol mounted baseboard elements on top of an Ashley Cabinet stove and ciculate it through his hot water oil fired boiler and it actually heated the whole house as long as stove was kept in wood!! Large house 3 or 4 bedrooms. He said stove heated basement and that was big plus because floor was warm and water was just an added bonus he was toying with idea for a while...(talk about the "good old days') another friend in Ashland had a nice home on a double corner lot...His mortgage payment ..a whopping $36 a month!

[weldingrodd]

I know  your right about the biggest loss going up the chimney!

I wish I could find a "Heat Saver " like I used to have that blew a tremndous amount of heat out of the hot air going up the pipe.....But in an affort to prootect us from ourselves I hear thay are outlawed! But i used on for over 20 years and never had one problem with it....But I was always to taught to burn a stove  like "blast furnace at least once or twice dailey and use only seasoned wood and you will never have a creosote proble.....and I never have had and never need to do more than clean the stove pipe clear of ashes once in a blue moon.

good luck with your Solar adventures..Its the way to go ..and finally this year I am tying a large lenth of 1 inch pipe 300 feet to pre heat water for my electric tank.

My area upstate NY has the distinction of highest general taxes in the nation and my county has slapped us with 30% property increase last year and 18% the year before that...Not mention the Power rates actually figure around 20 cents per kilowatt hr....so anything you can do to slow the meter down you should do it!

[weldingrodd]

Well the warm spell is over and I fired the stove.... and to my surprize 8 hours latter pipeing hot water!!(Thermo Syphon works great) Refilled stove and came home 9 hours latter to real hot water. Being first water heated in this used tank i drained all the water from it by means of both top (hot) outlet and bottom drain. Water was rather murky but hope its just old residue from tank. (Water was very hot even when I got to the 50 gallon mark) Remember my heat exchanger is mounted on outside of stove. If I move it inside I am sure it would increase my capability a lot.

When I get a minute i will post a pic of exchanger (can only see half of it but will get idea of how its made.

Making last pipe connections this evening  so I can either use wood heated water for preheated water for electric tank or can use wood heated water alone for domestic hot water just by moving a couple valves.

(What a nut i was for years...always bought the old globe valves and had troubles....I love the ball valves and wont ever use anything else again...Rodd

[jbthuis]

Hi - I just stumbled onto this forum and thought I'd share my experiences.  I have a large woodstove in my shop in the barn, and radient floor heating in the shop's concrete slab.  I wanted to heat the water for the floor with my woodstove, and so I put coils inside the stove. The idea was to use floor's small circulating pump to pump water from the floor through the heater-coil in the stove, and thus heat it.  This did NOT work - the water from the floor was just too cold and it caused massive condensation on the coils.  On to plan "B" ... I changed the design and put a 50 gal barrel on top of the stove to work as a heat exchanger.  Like I said, it's a pretty big stove!  I was able to just place the barrel on the flat top of the stove and hook it to the internal coil to the as a thermo-siphon.  Lastly I plumbed the floor to about 40 feet of copper tubing that is loosly coiled inside the barrel of water.  Now when I fire the stove, it thermo-siphons the water in the barrel, and heats the barrel of water to 150-160 degrees or more, depending on how hard I run the stove.  By the way, the barrel is loosly covered with a metal lid, so if the water in it should ever boil there is no danger of a pressure build-up.  To control the floor-pump I put a thermoswitch in a small metal box that just sits on the top of the metal lid of the water barrel.  As the water in the barrel gets hot, the switch heats up and clicks-on, and the floor pump starts circulating water from the floor, through the 40 feet of copper tubing, and back to the floor.  There are NO valves to worry about, and all I need to do is to run the woodstove - everything else is "automatic".  I've used this for 4 years now and love it!  You could do something very similar for domestic hot water, but you would need to be careful about the possibility of contamination if the heat-exchanger leaked.  I'll leave how you solve that up to you :-)  

By the way, I also have a standard electric hot water heater in series with the floor and the woodsove.  The water actualy flows from the floor to the hot water heater, to the heat-exchanger, and then back to the floor.  The hot-water heater is left turned off, but if I am ever gone for an extended period in the winter, I can turn the electricity to it back on.  That, in conjunction with a normal thermostat, works fine to keep the shop floor, barrel, tubing, etc from freezing.   It is a lot cheaper and safer than messing around with anti-freeze!

And a last comment - I also tried coiling tubing around the outside of the stove-pipe (and insulating it as well) but it didn't give very much heat at all.  In my opinion, having coils inside the stove is the way to go!

Stay warm - John