moving heat from a wood stove ?

[rustynut]

hi all,....i have a block room below the room that holds my wood stove and was thinking it would be nice to wrap some copper around that wood stove/pipe and pull some heat into the room below. i know you cant just cut a hole and set up a fan but was thinking you might pull heated fluid thru the floor and extract heat thru a radiator
which you could warm that room with? I lived in a home with a boiler & baseboard heating system and it was awsome. I'm just hoping for something that would keep the room 50-60 or so. That would be great for a little work shop. Any ideas on how to do this without extreme cost ?.......rn

 

[Fred61]

Most ideas like that usually end in failure. First problem arises when the water tube system actually works and is able to draw heat from the stove resulting in a poor burn in the stove from all the heat sucked from it. Poor burn causes creosote to form and diminishes the fire reducing the output. Unlike a boiler a stove is not engineered to be a boiler vessel.
Second scenario is that much of the time it won't draw enough heat to distribute and all the effort and money put into it is wasted. You'll need water make-up, perhaps a pump, expansion tank, and pressure reducing valve. The latter to keep an explosion from occurring. Even a hack that works inadequately can sometimes overheat if you lose flow and dangerously spew steam.
I've seen a couple of these in peoples copper salvage boxes.

 

[rustynut]

well i had to ask as the heater could ceiling mount in the lower room about a foot below the wood stove........
you say perhaps a pump?........are you saying convection will generate a flow ?

 

[Fred61]

I said perhaps because I didn't have my head completely wrapped around your project when I responded. You would need a pump but I don't want you to think I agree to that you should do it. I'm trying to talk you out of it.

 

[maple1]

Pretty sure convection won't do much in this case - you'd be asking hot water to go down and cooler water to go up. Backwards to the physics I'm aware of.

This isn't really a good idea, IMO.

 

[brenndatomu]

I agree with these guys ^ ^ ^. If you do this, I think you will be very disappointed with the results.
Now, I have seen guys put a roll of soft copper tubing into a panel that bolted to the side of the stove, and then use a pump to circulate the water through a section of baseboard...hafta put a pressure pop off valve in the circuit...and even then I would be a bit leery of it...say power went out and the valve stuck or something...copper, pump, baseboard...not really that cheap anymore either

 

[coaly]

More info is needed on the size and style of wood stove you have. Extracting heat from the firebox, not the stack may be fine if you have enough BTU waste and don't try to extract every BTU you can dropping stack temperature.
With a stove installed below the heated area, no circulator pump is required. Heated water rises, cools as it goes through radiation and drops to be reheated. Oversize lines help, and I've plumbed entire homes without circulators similar to a steam heating system pitched upwards to radiation and back down for good circulation. In your case you will need to pump it down to baseboard or radiation of your choice. You will need an expansion tank, relief valve and a way to keep system full. Normally a cold feed water line with low pressure regulator. Reasons for failure are not engineering the system properly, so you have to know how much BTU you're putting in the water, flow rate, and how much you are taking out. For example, a stainless 3/4 pipe (considered a coil) within the flames, like under a baffle plate or a stainless gizmo called "Hot Rod" is a commercially made U shape tube to heat water in firebox. http://www.yukon-eagle.com/FURNACES/THEHOTRODWATERHEATER/tabid/61/Default.aspx

The hotter the water at baseboard or radiator, the more efficient the heat moves into the air. 200 or more is best for efficiency, but you have to be careful not to create steam and open relief valve. A controlled flame in a gas or oil burner controls overheat conditions which you will experience with a stove, so the relief valve should be plumbed outside or into a drain. In the event of a power failure, a gravity system remains safe since it circulates at all times. In your case, a failed pump or electric failure which also supplies power to water pump that supplies the system may not be feasible. Antique boilers had steam driven water pumps and injectors manually operated to maintain water level without automatic safety devices but were constantly manned. There are no safeties on a wood stove to limit the heat output. (This is why you want black iron pipe or stainless sch. 40 in the firebox) Most stoves in Europe, Australia and New Zealand still use 'Water Backs" or water circulation of some sort. With the advent of oxygen barrier pex tubing (the tubing of choice) and automatic air vents (mounted at the highest point in system) it is easier than ever to design a good working system. You don't need high tech things like spiral air vents or air scoops, just a float type air vent to keep oxygen out of the system. (oxygen enters in fresh cold water when added if relief valves opens) I connect the coil with flexible stainless water heater connectors before going to pex in case it runs dry. I have a gravity system on my Kitchen Queen with 25 gallon tank on the stove built for Amish use without electric. It is an "open" system used in many Amish households without circulators or electric power.
Here's a really good book on the subject.
http://www.archive.org/stream/kitchenboilerco00unkngoog#page/n72/mode/2up

 

[erollins]

I would suggest that it would be much simpler to move some warm air from the stove room to the room below. Something like a 4 inch diameter duct using a bathroom vent fan would be simple, and a couple of 4 inch holes between the rooms wouldn't be much more work than a couple of one inch holes for water pipes

 

[rustynut]

well i was just tossing the idea around and thought i'd check........... It sure would be easier to drop a 4 inch in but i think i heard something about that being against code?....... thanks for the info guys. rn

 

[Seasoned Oak]

You would probably have to draw the air from above the stove,then you would need a strong fan to force it down. A bathroom vent fan is way to weak for this application. I think trying to do this with water would be time consuming,costly and not work anyway. IMO