Woodstove hot water-how much would be too much/too little

[acs55812]

I am going to try and heat water on my wood stove via a copper coil under the side/rear heat shield, or a heat exchanger similar to this under the heat shield ( http://www.americanroyal.net/page/page/4344281.htm ), and/or a box on top of the stove with water running thru it.

I don't have any concept of how much convection it takes to get enough heat to warm the water----it is conceivable that I could run the water thru the box on top---and around three sides before it exits the stove----but I have no idea if the water will be as hot as it can get by just mounting one "radiator" on the side of the stove and all the rest would be over kill as the water would have picked up as much heat as it can carry thru just on coil vs. three coils and a box. (Hopefully the way I explained that makes sense).

All the water at/on/near the wood stove will be unpressurized---open to atmosphere in case of boiling/power loss for circ pump. I plan on using this hot water thru either a side arm or plate type heat exchanger to supplement fin tube radiant heat.

 

[NH_Wood]

I don't know about the exchanger shown in your link - doesn't seem to be enough coiled copper to get the water hot, but perhaps there is enough. The best design I've seen for an 'outside the firebox' exchanger was a project I saw on Mother Earth News website: http://www.motherearthnews.com/do-it-yourself/woodstove-water-heating.aspx. I think the 60' or so of copper coil would get the water fairly hot. I was thinking about setting a similar structure against the back of my stove, since it sits above my hot water boiler downstairs. Was thinking of buying a cheap electric hot water tank, and at least using pre-heated water from the stove, into the tank, and then draw from that hot water when my boiler demands water - rather than the cold water from the well. Haven't done much except think at this point. Lots of issues to think through with hot water and stoves (steam pressure dangers, possibility of excess creosote if you are directly stealing heat from inside the firebox to heat the water, etc.). Good luck!

 

[WES999]

The heat exchanger in the link appears to be a water to air model.They are ment to be installed in the air duct of a hot air heating system. I doubt it would provide much hot water if placed on the back of a stove. Wood stove heating of hot water is generally used to heat DHW not for radiant heating.

My wood stove water heater has an external heat exchanger on the side and the top and an internal SST loop inside the stove. It will heat 100 gl of water in several hours. I think I calculated about 16000BTU/hr. OK for DHW but I doubt I could heat my house with that.

I would guess that with just an external heat exchanger your out put would be considerable less.

 

[DexterDay]

There was a guy in the Pellet Mill that put 2 radiators on an Englander pellet stove. 1 on each side. I will try to find it. Pellet stoves give off little radiant heat. If he could do it. I am sure you could get by.

 

[acs55812]

I should clarify since I wrote the first post quickly.

I am not looking to use the woodstove as a primary heat source for the baseboard----my situation is that if I run the woodstove "good" or "lots" I can go in some cases 5 or more weeks without the oil boiler coming on. During that time period, in my ranch style house the far corner of the kitchen and bedrooms can get VERY cold with only radiant heat off the stove in the living room---and in some cases with the baseboard water not moving for 5 weeks I can get slush/ice and it won't circulate when I could use the oil to kick on for awhile.

My mission is to take some percentage of heat off the woodstove---have it heating water that would be applied to the fintube thru a plate heat exchange or sidearm arrangement, with this woodstove heated water circulating 7/24---AND open to atmosphere so I don't create a steam bomb if I loose power to the circ pump---if only to get a small amount of heat circulating while the oil boiler is not running. Thereby keeping the current pressurized fin tube system in tact, with the wood stove heat being in a additional circuit that would not interfere with the current system (That part I got figured out, just gotta get a concept of heating water on the woodstove.

Between some warm water coming from the stove and the fact that moving water can't freeze---I am hoping for some (not alot but some) additional comfort in the far corners of the house---and since its moving all the time if I do need the oil boiler it could function since it wouldn't be froze.

In the above pictures/links it was for a reference to get your opinion of what would transfer heat in the most efficent manner----a simple copper tube coil like in the Mother Earth News article, a alum. and copper arrangement like a car radiator, or a tank on top of the stove---I am trying to narrow down how much is necessary vs "that is way overkill" as the water would be heated when it is half way thru that path on the stove.

 

[madison]

IMHO, it will not work. Plus it will look like poop if the woodstove is in a living area. Boil overs or "working too well" will be the least of your concerns.

You will need air flow over the aluminum fin radiator to function. Same with your copper ideas.

Solar panels can be mated to hydronic systems, but are costly.

Moving water can freeze. You may wish to add glycol to reduce the freezing point, and periodically "excercise" you boiler, ie use a timer thermostat and have it come on for a few minutes a few times each day.

 

[raybonz]

I don't know about the exchanger shown in your link - doesn't seem to be enough coiled copper to get the water hot, but perhaps there is enough. The best design I've seen for an 'outside the firebox' exchanger was a project I saw on Mother Earth News website: http://www.motherearthnews.com/do-it-yourself/woodstove-water-heating.aspx. I think the 60' or so of copper coil would get the water fairly hot. I was thinking about setting a similar structure against the back of my stove, since it sits above my hot water boiler downstairs. Was thinking of buying a cheap electric hot water tank, and at least using pre-heated water from the stove, into the tank, and then draw from that hot water when my boiler demands water - rather than the cold water from the well. Haven't done much except think at this point. Lots of issues to think through with hot water and stoves (steam pressure dangers, possibility of excess creosote if you are directly stealing heat from inside the firebox to heat the water, etc.). Good luck!

I look forward to hearing how that works for you.. Perhaps if you have a circulator running the stove heated water into a well insulated tank you may get decent results..

Good Luck!

Ray

 

[begreen]

Do yourself a favor and shelve this idea for a month or two. Instead, try putting a simple, 12" table or box fan on the floor in the cooler area and point it toward the stove area. Run the fan on low speed. This approach has helped a lot of folks even out the room temps with ranch layouts. If it works you'll save a lot of money and hassle.

 

[fishingpol]

Cooler water in an exchanger can cause the coil build up condensation on the outside, you may end up with a dripping mess. On the Build it Solar website, I believe Gary used a solar panel with a well insulated storage tank in a crawl space to pre-heat water going to his hot water tank therefore reducing fuel usage to heat the water. I think your project has some challenges.

I am looking into an outdoor boiler reset for my gas boiler. It has an outdoor temp sensor that measures the temp and sets the boiler water temperature based on that. On cool fall and spring days, the boiler is automatically adjusted to run a few degrees less. On cold winter days, it runs the necessary temperature. Not fiddling with the aquastat. They claim up to 15% fuel savings. You just can't set the temp too low that the return water condenses. Your circulator will run a little bit more to extract the heat out.

The BIS website may have some tips and ideas for you. Good luck, we like to see pictures in progress. I will be updating my solar heat box collector for my basement in a few weeks.

BTW NH Wood- nice link to that project.

 

[firefighterjake]

Far be it for me to discourage experimentation . . . but I'm a firm believer in keeping things fairly simple.

In my own case it can get pretty darned cold here in Maine in the winter and I was worried about water pipes freezing -- both domestic supply lines and the water in my oil boiler pipes. However, in three years this has not been a problem even though I pretty much run the woodstove 95% of the time.

As BeGreen said, moving the heat to the distant areas of the house can often be easily obtained by setting up a fan on the floor to establish an air flow -- cooler air near the floor is pushed towards the hot stove where it is warmed up and it flows out near the ceiling height to the area displaced by cooler air . . . it sounds crazy, but it works and running a fan is a pretty cheap way of moving heat in a house heated by a woodstove.

Now I also am one of those guys who believes in suspenders and belts -- well not really . . . mostly I just wear a belt, but you know what I mean . . . which is why I have my oil boiler to kick on at around 60 degrees in case I don't get home when planned, the weather gets very cold overnight and I don't bother getting up in the middle of the night (which is typical) or for those times when I just want to get away for a while . . . this is my back up plan . . . with three zones this insures that most any area in the house will not get below 60 degrees + or - a few degrees.

Finally, I take no chances . . . even though I know the earth should keep things from freezing underneath the house with my crawl space/basement (it's about a 4 and a half foot crawl space/basement) I don't quite trust Mother Earth well enough when the sub-zero temps hit us . . . when this happens I typically crank up the oil boiler once or twice a day to move some nice heated water through the pipes to warm things up and keep things moving a bit.

Oh yeah, one other thing . . . I didn't do a search, but one of our long-time members here builds and sells gizmos that hook up to your existing thermostat which will circulate the water in the pipes to keep things from freezing . . . unfortunately I cannot remember the guy's name (Black Bear, Badger, something like that) or the product name (Therm Gard or something like that. . . . which I now realize provides you with absolutely no useful information . . . maybe someone else can provide a member name, link or product name.

 

[jimbom]

If you do run water in or near a wood stove, please put a pressure relief valve directly on the inlet and one directly on the outlet at the stove. No valve of any type between the prv and the stove in either case. These installations can fail in unexpected modes. Rarely happens, but worth protecting against.

 

[acs55812]

ok---this project is likely dead, since I just picked up one of these---now I just gotta figure out where to install it to make getting firewood to it easy!

I haven't seen the owners manual yet, there is no name on the stove but the owner is "sure" its a Kuuma brand---the boiler was at her Dad's house and the owner manual is at her house. (which also means there is no UL label on it either)

Also does anyone know what/how the electrical box on the bottom left would work to control the draft? And also the very fine white powder all around the door---what might cause that and is it anything to be concerned about?

 

[DexterDay]

The White looks to be a slight indication of an overfire situation. IMO. I could be wrong. But based on the color and the way its on the front of the firebox. Maybe they did not have the electrical draft/thermostat hooked up, or hooked up correctly.

Congrats on the purchase. Look for any warped or cracked parts.

 

[acs55812]

I did look throughout the firebox, couldn't find any warped parts inside---will of course do a better inspection when I get it home---the electrical box---is it to be hooked to a wall thermostat to open/close the air damper----or tied into the water temp to control the air damper? Could you/someone lead me to an owners manual of a stove you think has and equivalent box so I can see what it is and how its supposed to work?

 

[begreen]

Moving this to the boiler room forum for better domain experience there.

 

[raybonz]

The White looks to be a slight indication of an overfire situation. IMO. I could be wrong. But based on the color and the way its on the front of the firebox. Maybe they did not have the electrical draft/thermostat hooked up, or hooked up correctly.

Congrats on the purchase. Look for any warped or cracked parts.

+1 I agree that sucker got pretty hot!

Ray

 

[acs55812]

After getting this home, and closer examination---I don't think it over fired at all, it looks like due to the door gasket being compressed a bit and/or the door not being adjusted for proper air tightness this is more of an ash leak or possibly a defect in the paint used on that portion of the boiler--it flakes off with fingernail scratch---and the actual door nor the little inspection door thing above the stove loading door has it stuck on it.

Anyway, now I want to do a test burn on this boiler this week, I want to do this for my own comfort level before punching a hole in my garage roof for a new chimney.

I am thinking of putting a couple 4 foot sections of chimney on the boiler and hooking it up to a 50 gallon metal barrel of water for a total of about 75-85 gallons or so of water circulating just to see the results and know there is no surprises like water leaks and such. Am I missing anything for a test burn like this?

I am also thinking a pressure test of _____ pounds for ___ days would be a good idea to verify its not leaking slowly anywhere too. (Please fill the blanks in for me on what would be a decent test)

 

[bpirger]

So you plan to burn the unit outside with the drum of water and a circulator? That will look interesting...but I'd be very cautious as well. Boiler systems usually have a blow off valve set at 30psi, so if you pressure test to 30, you should hear the blow off open. Make sure it does....might even want to put a new one on just to be safe. Sometimes these things will gum or a get debris in them, etc. My experience is that makes them hard to "close", i.e. junk in the valve seat. So I'd say 28 PSI overnight should tell you that there isn't a leak.

If it is Kuuma, they have a presence here, you should be able to get all the info you need from them...

Good luck!

 

[Frozen Canuck]

AFA what to do for the test - remove all the boiler skin that you can before firing, you will want to see any small leaks that could evaporate under the skin & therefore go unnoticed for a long period. Find the Mfg plate on the boiler or verify make/model, from this find the max operating pressure of the boiler. Do not exceed the max pressure rating. Start with a small fire & work up to a larger one, far easier to throw out a little burning wood in the event of a major issue. Do your test in an area that you can get ample to water to just in case, preferably away from other buildings, having a garden hose ready to use would not hurt. I am sure some far more experienced members will chime in with some good been there done that advise. Until then this should get you started. Enjoy the process & the learning & stay safe.