wood stove, fresh air intake size?

[flingwing1969]

The fire cycle.

 

[Paddy]

Randi41,

Fire needs air, if you don't provide piped outside air, it will pull your heated air from with in your home. That air will draw a negative pressure. Outside, cold air, will seep in from cracks and gaps. You may not notice it.

Piped in air is not required, but it will lower your fuel consumption.

 

[KennyG]

It does depend on the house to some extent. All houses have a pressure differential in winter with higher pressure being at the upper elevations, due to buoyancy. The air then will try to leave through any openings (which will exist no matter how tight you try to build). Not such a big deal with a one story house but in my case of two story house with a basement, the negative pressure in the basement is very noticeable. I have a wood stove in the basement and if I did not have an outside air intake, I would have to open the walk out door to get the stove to burn well. That is in spite of having fresh air vents (with traps) in the basement. As noted 4" works fine. All the ones I have seen have 4" connections.

 

[randy41]

i looked on the web and didn't find any scientific studies. most of the info is based on logical thinking. it seems like if you don't have the outside air going directly into the stove then you can accomplish the same by opening a nearby window a little.

 

[Raspy]

Not picking sides here, but any air going up the flue/chimney is coming from the fire box. The same amount of air going out through the flue has to be replaced, so its coming from either the room/house, from an indirect outside source (like I listed earlier) or from an OAK. If it's coming from the room, that air then has to be replaced which typically is through cracks and crevices around doors and windows. There's no way around it, a fire will be consuming air.

Of course this is absolutely true.

A dedicated air supply only defines where the air is coming from. Without it, that air is coming in through cracks, or bath vents, or open windows, or whatever. It's a very simple fact that if the fireplace is burning, air is entering it and that air is coming from somewhere. Traditional fireplaces are famous for only heating the room they are in because their combustion air is coming in through leaks in the rest of the house.

It amazes me that someone could not understand that fireplaces use air, and that that air must come to them from somewhere. I've actually had people tell me that a gas furnace doesn't need an outside combustion air supply if it is in a big room. What?

As to an earlier comment by one poster that the air pressure was higher near the ceiling than lower, or in the basement. Not so. Warm air is less dense than cold air, so it rises. This is how a fireplace chimney works. Same thing as oil floating on water in a bucket. Same pressure, but different weight materials. Not differnet pressures.

And that's why it is important to have a ceiling fan to stir up the stratified air in a fireplace heated home. Otherrwise you are sitting in the coldest air in the room. Down at the bottom.

 

[KennyG]

As to an earlier comment by one poster that the air pressure was higher near the ceiling than lower, or in the basement. Not so. Warm air is less dense than cold air, so it rises. This is how a fireplace chimney works. Same thing as oil floating on water in a bucket. Same pressure, but different weight materials. Not differnet pressures.

And that's why it is important to have a ceiling fan to stir up the stratified air in a fireplace heated home. Otherrwise you are sitting in the coldest air in the room. Down at the bottom.

No, it is absolutely true. If you open a window on the 2nd floor of my house, the air will go out and if you open one in the basement air will come in. The pressure outside is the same both places so the pressure must be higher upstairs. Buoyancy is based on differential pressure, not a force in itself. Less dense material rises because the difference in density causes a pressure differential.

 

[lennyzx11]

I have a two story. The upper is heated/cooled with a split ac unit and the bottom with a heat pump a la central air ducts.
Though the ducts and registers are correctly sized and well insulated, I find that I can open the nearby window by my wood stove and the stove burns much better.
I would think that the pull through the ducting would be sufficient.

I've been on the fence about installing a dedicated intake for the stove and am following this thread with interest.

 

[oosik]

When we had a wood stove - I drilled a 4" hole thru the side of the house, installed a 4" plastic pipe and fine mesh screen covering both ends of this pipe. It seemed to be sufficient to adequately supply the wood stove. I'm sure if it wasn't - air was also drawn from the basement vents. I capped this pipe in the summer when the wood stove was not in use.

 

[Egon]

Hot air goes up! Cooler will rush in to replace it!

Air pressure and air density are separate entities.

Air pressure generally decreases as altitude increases. Boiling point at elevation!

 

[Groo]

One idea I am kicking around would be to put a second hole into the chiminey under the main stove pipe and use that to draw air in throught the cleanout. I figure that would completely eliminate the inversion risk (what miniscule risk there might be) and look better.
Anyone see a downside to this?

My idea of a fan on the inlet would be to mainly get the secondary burn going and get the chimeny drafting properly. One going, I don't think it would be needed.

On a realted note, the first thing I was going to try was a Draft Inducing fan on the exhaust pipe, so picked up a Tjernlund AD-1. Auto Draft Stove Blower AD-1 – Tjernlund Products Retail
It had a big hole in it (maybe 1.5" or 2" diameter), so I contacted the company thinking a cover was missing and they told me to "never cover it. it is needed for cooling."
Q"so what happens whent he power goes out? won't smoke get in the living space?"
A"don't use your stove when the power goes out."
Q"WHAT? so I'm supose to shovel hot coals and burning logs out of the stove if the power goes out, and hope it only happens when snow is on the ground?"
A"well do you do that now?" yah..not much of an answer.
Q"won't this hole drastically increase my negative pressure and heating costs"
A"we've sold thousands of these and nobody is complaining"

needless to say, that product got returned.