Fireplace/Wood Stove Combustion Air

[dmccarty]

What does the TBN Brain Trust know about supplying combustion air to fireplaces and wood stoves? I have searched the Internet and found some information but not alot.

My FIL has a massive stone fireplace in his house. Its big enough to be used as a divider between the living and dining rooms. He heats his house with the fireplace in the winter. When the house was built he had a pipe put it the slab that runs from outside to the front of the fireplace. He has a vent right in front of the fireplace that he opens to allow outside air to be used by the fireplace. It gets a good draw of air when the fireplace is running....

Our house will be have at least one wood stove. I had a six inch PVC pipe buried under our slab and it runs to the wood stove hearth. We will do what the FIL is doing with his fireplace in that we will terminate the pipe with a vent that we can open and close as needed to supply the stove with outside air.

The only website I can find says that outside air supplied through pipes is problematic. That direct connections can back draft. Ours is not a direct connection so I don't see that as an issue. Combustion air has to come from someplace and our house is going to be very tight. ALL the windows are casements. I'm caulking/foaming every opening I can find as the house is being built. We have 2x6 walls, covered in 1 inch rigid insulation, 1/2 inch OSB and finally brick. Its going to be a tight house. /forums/images/graemlins/grin.gif

We are thinking of putting in a second wood stove. It comes and goes in our plans. The house has reached a point where we can see things and a second wood stove would be nice for a variety of reasons. Now the second stove does not have a combustion air pipe nearby so we would have to depend on the air from the pipe on the other side of hte house or put in a second pipe in a wall going to the attic to get the air. We don't know if this will meet code or not.....

Opinions?

Later,
Dan McCarty

 

[Jim_Fisher]

Dan,

</font><font color="blue" class="small">( We are thinking of putting in a second wood stove. It comes and goes in our plans. The house has reached a point where we can see things and a second wood stove would be nice for a variety of reasons. Now the second stove does not have a combustion air pipe nearby so we would have to depend on the air from the pipe on the other side of hte house or put in a second pipe in a wall going to the attic to get the air. )</font>

I don't think that a stove will draw enough air to be an issue.

I've used both wood stoves and a fireplace for supplemental heat. An open fireplace will allow air to be drawn above the fire and up the chimney. That can be a major source of heat loss. The problem doesn't occur with a stove.

With a fireplace, an insert or glass doors will minimize the problem and improve efficiency.

 

[Junkman]

We have a pellet stove in the living room and when it is in use, there is a current of cold air that comes across the floor to feed the appliance with combustion air. This isn't the intended direction that I tried to provide combustion air, but since the "intended" pipe isn't sufficient to supply enough, it will find its own "make up" air source. As you have pointed out, you will have a very tight house. This can be a bad thing unless you provide for some way to exchange the air from inside to outside. My home is also very tight, and we installed a make up air damper in the cellar. Any time the inside air becomes a "negative", the damper opens and allows air into the basement. Our 20 year old system is on the crude side of the design factor as compared to what is presently available on the market. There are electric units that will exchange the air and extract the heat from the house are and mix that heat with the incoming outside air. They also clean the air coming in through the unit.

 

[PineRidge]

When they built my place they brought in outside combustion air to supply my gas logs. The fresh air is channeled from the soffit area. As I remember the size was 4 inches but that amount would need to be changed according to your own needs.

 

[hazmat]

Dan,

When we put our stove in I looked into this a little bit. Vermont castings has an "Outside air adapter kit" available. I assume it is for the direct connection you mentioned. Our house is relatively new - 9 years old, but isn't super tight. Stove runs fine w/o outside air supply.

Someday I'd like to build a timberframe house with the wall panels. In the process of my daydreaming/research I've found these make for extremely tight houses. They put in the air exchangers that Junkman mentioned. Probably a good idea just to get fresh air regardless of wood heating.

I'd contact the stove manufacturer. The stove dealers/installers don't seem to be very "technical" at least around here.

 

[PineRidge]

Junkman Skuttle makes a unit like you are describing. We used to install a lot of them in newer construction. Skuttle click here

 

[SPIKER]

I would say you SHOULD have some sort of cold air make up:

reason being, you're inside air can get pretty bad on supper tight homes very fast. start BURNING the O2 and soon you're house becomes a carbonmonoxide death trap very fast. make sure you install good monitors for carbon monoxide !

I would install something like what PR posted making you're OWN is pretty easy, if you find you want to do that. you would still need all the cold air pipeing, and then a damper on one end or the other, which would be a ballanced unit, so that any draft, causes it to open and lack of draft it will close. (Heavy nut on a all thread rod works to do this, and can be welded or bolted to the pivioting damper) Also you can install this to draw COOL air in through a heat exhanger which is in-line with the out going hot gasses. (such as a 6" tripple walled flue, with a single wall 12" flue to bring the make up air in through the same path the HOT air exits, thus warming the incomming air some.) might take some creativity but it does work. you can't cool the out going air too much, but that shouldn't happen anyways as most wood stoves are not very efficient...

Also with tight houses inside mold can become a very big issue, as can Mildue and or ROTT of the siding...

We were in a house which was less than 10 yrs old, due to MOLD/MILDUE the OSB was gone, you could poke you're fingure through it!!! the Owner/Builder thought at the time it would be helpfull to wrap the home with PLASTIC (not tyvek or pereferated type breathable material) actuall PLASTIC sheeting. this was under the vynal siding and then 1" ridged foam over the poly/plastic sheeting... he built it right to stop any drafts! had many problems with the HVAC system getting enough air, had to put in a make up air unit powered when ever heat was on. .. they actually condemmed the home if I remember right, we were in th take a look at reparing it... after 15 min in the house holding our breath was too much exhaled outside and ran!.


Mark M

 

[Junkman]

Mike ....... thanks for the link....... the one that is presently installed is a commercial unit that is tied into the cold air return. If the house goes negative, the damper opens and sucks in fresh air from the outside. It doesn't have any electrical parts and I never know when it is working. I do know that there is a draft that comes up from under the cellar door when the pellet stove is running. I also have a 2" PVC pipe from the cellar to the pellet stove that matches the opening on the back of the stove for fresh air intake. It is just that 2" isn't enough fresh air for combustion. I will be looking into drilling a larger hole through the floor in the future to eliminate this "draft".
I also found some other information while at that site and will be posting a new question in the forums about that information.... thanks again...... Junk

 

[Egon]

About the simplest air make up system for a house is a pipe from the outside with a 90 degree downpiece inside that ends in a bucket. No flapers -- no moving parts - - also no heat echchanger

Egon

 

[PineRidge]

You're welcome Junk!

If you guys are using anything but electric to heat your place I would also recommend a good carbon monoxide detector. Not one of the detectors that just has a buzzer but one that reads out in PPM (parts per million) so you will know exactly if and how much build up that you may have in your home.

I have a Nighthawk mounted in my home and it's extremely accurate. It's also affordable, I believe that I paid about $45. for it some years back. It will give you some peace of mind. /forums/images/graemlins/grin.gif