Cold air intake for stove

[strategy400]

I'm planning to run an air duct up the wall near my stove to draw cold combustion air from the attic. I also have a furnace in the attic that may draw combustion air. I have large vents on the roof and gable vents.
1. Is this advisable?
2. Where can I get a 10 foot duct that won't look hideous running up the wall. Trying to avoid seams.

 

[EatenByLimestone]

I'd try not to draw cold air through anything that has the capacity to act like a chimney. Can you go out a wall below the stove?

 

[begreen]

I'm planning to run an air duct up the wall near my stove to draw cold combustion air from the attic. I also have a furnace in the attic that may draw combustion air. I have large vents on the roof and gable vents.
1. Is this advisable?
2. Where can I get a 10 foot duct that won't look hideous running up the wall. Trying to avoid seams.

It's definitely not advisable and most likely warned about in the stove's manual. A setup could turn that air intake into a chimney with disastrous results. The air intake should ideally be below the firebox.

 

[strategy400]

OK. That makes total sense. I'll have to run a longer duct to a wall to outside. Thanks for your sage advice guys.

 

[strategy400]

No wonder I've never seen that.

 

[begreen]

OK. That makes total sense. I'll have to run a longer duct to a wall to outside. Thanks for your sage advice guys.

How long? If over 10' it's not a bad idea to increase the size by an inch to reduce resistance.

 

[EatenByLimestone]

Why do you think you need outside air?

 

[mar13]

Why do you think you need outside air?

Wouldn't using outside air be more energy efficient? You aren't using heated indoor air for the stove which is then replaced by cold outside air? I'd probably use an outside air kit (OAK) if it were reasonably feasible for my hearth set-up.

 

[Woodfire2019]

Phew, glad you asked this question! Could've saved a lot of damage or worse it sounds like.

 

[EatenByLimestone]

Wouldn't using outside air be more energy efficient? You aren't using heated indoor air for the stove which is then replaced by cold outside air? I'd probably use an outside air kit (OAK) if it were reasonably feasible for my hearth set-up.

Whether it's more efficient is a hard question to answer. The stove port for outside air isn't air tight (I think you'll be surprised at it if you look closely at the system) , so you are still drawing air from inside.

Unless your house is sealed so tight that the fire is having a hard time breathing, I think it's a hard sell that cutting a 7 sq inch hole in the wall is a great way to increase efficiency. Try opening a 24" wide window 1/3 of an inch. Same idea, but I suspect you wouldn't call that efficient.

So, the next question that I'd ask, is how much air is the stove really using? Could it use 7 sq in of air intake if it had it? Find the air inlet holes for the primary and secondary air systems. There's often a doghouse air inlet too. Your phone or a mirror can really help see the bottom of the stove.

Close the primary and secondary air down like you would for a mature, cruising stove burn. The open area that the stove can get it's feed air is really small. It's not pulling much air in.

So, stoves don't really pull much air out of the house. If your house is so tight that it needs a hole cut in the wall, thats 1 thing, but for 99% of houses...

 

[electrathon]

Wouldn't using outside air be more energy efficient? You aren't using heated indoor air for the stove which is then replaced by cold outside air? I'd probably use an outside air kit (OAK) if it were reasonably feasible for my hearth set-up.

It can aid in draft on a tight house. It will always help more heated air stay in your house. The stove air inlet will always draw in the same amount of air as is leaving your chimney going out. If your house is drafty and you do not object to pulling cold air in through the small holes all around your house, then through the house, cooling the house till it gets to the stove and goes up the chimney, don't worry about it.

 

[mar13]

What's a rough guess on the volume of air pulled through a chimney when a fire is going strong? (Sorry, drifting off thread topic.) I have zero idea and imagine it depends on many factors.

Yeah, I can see an OAK letting cold air into to the house, and not just the stove, especially when the stove is not in use.

 

[EatenByLimestone]

Please excuse the soot in the pipe. It was cold, I was cold, and I should have turned the pipe 90 degrees when I installed it, lol.

My stove runs just fine with this key damper closed and the stove damper closed.

You can see there isn't much room for the air to go through it. But the total volume of my chimney can be seen in the pic below.

 

[EatenByLimestone]

Ugh, looks like I got my radius wrong. Should have been .25. Well, updated numbers are 3.53 cubic feet.

 

[rwhite]

I'm with the others on this. Unless your house is so tight a fire won't burn I wouldn't bother. Some air exchange is not a bad thing. Much more air being pulled in by a bath fan or just walking through a door than by the stove. Do you have a basement or crawlspace below the stove?

 

[coreboy83]

What about pulling air from the furnace room (on the other side of the wall) that has a fresh air for combustion ? Can a person hook OAK directly into that room ?

 

[rwhite]

What about pulling air from the furnace room (on the other side of the wall) that has a fresh air for combustion ? Can a person hook OAK directly into that room ?

I would not do that. Even though furnaces draw air from other areas of the house they are not air tight. Strong possibility you'd pull smoke through the OAK.

 

[strategy400]

Yeah definitely glad I asked the original question. My house is pretty tight we live in the california high desert so it gets really hot in summer. It's about 16 feet to the exterior wall. House is on concrete slab. It's this stove http://pdf.lowes.com/operatingguides/794909501514_oper.pdf

 

[Das Jugghead]

I can attest that installing an outside air intake made a HUGE difference in the comfort level in our home. Our windows leak a lot air and need to be replaced. Last year we could actually feel cold air migrating across the floors in our house toward the stove. I custom built an air tight intake kit for our stove and it made a very noticeable and measurable difference in the efficiency of heating our of our house. Last year we struggled with maintaining 70 degrees - now we rarely dip below 70. Most of the time we average 73-75 degrees. The other night with outdoor temperatures at 19 degrees we hit 81 degrees in the room where the stove is located.

If a stove is drawing its combustion air from the building envelope that air has to made up from somewhere and that somewhere is from outside. That outside air entering the living space is cold and brings down the house temperature while robbing the house of the heat the stove is producing.

A bathroom exhaust fan or a clothes dryer may move more air than the wood stove in terms of CFM's but they only run periodically whereas we run the stove 24/7. For us the woodstove is our primary source of heat.

My two coppers for what they are or are not worth. Your experience may differ.

 

[Poindexter]

I agree with @Das Jugghead . Combustion air for the stove is going to come from outdoors through the path of least resistance.

In my home, the stove is on the upper of two floors, with a nearby sliding glass door onto the deck. On the lower level, I have a fairly significant air leak under the entry door. If I blow spray insulation under the entry door on the lower level I fully expect makeup air for the stove will come around the silding glass door on the upper level.

So I haven't "fixed" the air leak under the entry door on the lower level despite annual badgering from my wife. The upstairs is quite warm, the floor of the foyer downstairs is cool.

 

[littleboss]

Couldn't you just run a 4" piece of pvc pipe in through the wall and stop it right behind the stove. The stove should pull air from there since it's close to the stove. Shouldn't have to be attached to the stove. You could put a blast gate on it (like used in a woodworking shop dust collection system) to shut off the air when not burning the stove.

 

[strategy400]

Good idea except PVC is a combustible? I suppose PVC run to clearance area then dryer vent from there.

 

[Das Jugghead]

@strategy400 does your stove have the ability to connect the outside air intake directly to the stove? If so then this would be a much better approach to providing combustion air than simply terminating the fresh air feed somewhere near the stove.

 

[rustynut]

How about insulating the osa pipe up to the stove ?...

 

[MissMac]

I agree with @Das Jugghead . Combustion air for the stove is going to come from outdoors through the path of least resistance.

In my home, the stove is on the upper of two floors, with a nearby sliding glass door onto the deck. On the lower level, I have a fairly significant air leak under the entry door. If I blow spray insulation under the entry door on the lower level I fully expect makeup air for the stove will come around the silding glass door on the upper level.

So I haven't "fixed" the air leak under the entry door on the lower level despite annual badgering from my wife. The upstairs is quite warm, the floor of the foyer downstairs is cool.

I have this exact problem at my place. We have a sliding patio door about 8ft in front of the wood stove, and it sucks air through the bottom of the stationary piece pretty noticeably. With the cold temps in the -30s, i get actual frost condensing where the air's coming in. It doesn't make me very happy since it's a new door, but I get why it's happening. I might try to shore up behind the trim with some more spray foam, but there's really not much I can do for the air leaking through the door unless i install and OAK, which really doesn't work in my place.