Coalpail.com Forum

Can't exhale more than you inhale

Lightning wrote:So Larry did a fine job of answering the million dollar question of how much room air goes up the chimney thru the barometric compares to average air infiltration of a house. It seems a low percentage.

Now for the two million dollar question which I must agree would be based mostly on speculation. Ready? lol

Does the barometric ADD air infiltration into the home OR would the additional air passing thru the barometric slow down air that's leaving the house up above it? Which would keep overall air infiltration the same.

In other words, would it lower the neutral pressure plane (due to stack effect of the house) or would it raise it? Given that the house is equally sealed on top and bottom.

Less air infiltration because of lowering the draft.
By reducing the draft in a chimney, a baro reduces the need for make-up air (from wherever). The air can either go through the stove or through the baro. Stove= more draft, baro = less draft.

Like Carbon just said, you can't exhale more then you inhaled. While a baro indeed uses warm room air, by lowering the draft, it uses less warm room air then the stove would have.

And reduces pulling hi heat out of the stove. So there is a net heat gain with the baro at the same time reducing the house air leaks caused by chimney draft.

Not to insult anyone. I find it very interesting how such a simple device can seem so mysterious and be so misunderstood.

Paul

I think that's a good stab at it,The only thing that bothers me is that I believe more room air is is leaving the house thru the chimney with a barometric than just thru the combustion air controls alone. Especially when there are points of high drafting and the barometric door is open a generous amount.

But, It's also true that the air is lessened at the combustion air controls due to the weaker negative pressure the barometric is causing. I believe the two added together has more room air leaving the house thru the chimney than the combustion air controls would by themselves.

That's the whole beef with a barometric to me. It causes added air infiltration.

I think I've come up with a solution for the two million dollar question. Barometric or not, the stove uses room air. This loss of room air thru the stove would drop pressure in the house. The drop in pressure would slow down air loss at the top of the house and at the same time help air infiltration at the bottom.

So it stands to reason that only half of the air that the stove uses is replaced with added cold air infiltration. The other half is air that would have left the house at the top but couldn't because of the lower pressure in the house.

How you guys doin? I got a headache hahaha

Actually, the stack effect and heat loss is caused by the difference in temperature between inside the house and outside the house. The greater the difference (how warm you like your house) the more infiltration. Your coal stove is causing more infiltration as it heats your house. It is evil and must be punished!

Yes!!! Punished!! Her sentence it a firm slap on the hind quarter!

Yes sir, I understand the stack effect principle and applying that in conjunction with air in equals air out along with the consideration of what the stove is using. Hahaha

Given the chimney is drawing air out of the house and all of that air is replaced by air infiltration from outside.
Also given, the air going out of the chimney should help create lower pressure in the house.

My speculation is that this lower pressure moves the neutral pressure plane higher. That being said, the lower pressure in the house would encourage cold air infiltration but up higher it would inhibit warm air from escaping. This concludes to me that half of the air going up the chimney is additional air infiltration. The other half is air that would infiltrate whether the stove is there or not.
But since the stove is there and it is creating negative pressure in the house, the other half of that air is air that couldn't escape above the neutral pressure plane.

Maybe I need a vacation.

Again,....my brain hurts Mr. Gumby!

I purchased an 8" Fields Control RC damper a few weeks ago (not yet installed). I notice that even in the fully closed position there is a 1/8 gap around the damper flap, it seems to me that in a low draft situation this could cause a no-draft situation in the firebox, or cause CO to vent into the home. Does anyone make a baro that closes fully? Would that not be a better design?

It depends on how your stove is designed but most likely if there is a no draft situation then there will be CO in your furnace room regardless of how well the chimney connector is sealed. As long as the air in your chimney is warmer than the outside air and you have cracks for air infiltration it is unlikely that you will have no draft.

dalmatiangirl61 wrote:I purchased an 8" Fields Control RC damper a few weeks ago (not yet installed). I notice that even in the fully closed position there is a 1/8 gap around the damper flap, it seems to me that in a low draft situation this could cause a no-draft situation in the firebox, or cause CO to vent into the home. Does anyone make a baro that closes fully? Would that not be a better design?

Under normal circumstances, the gap is not an issue. As long as negative pressure in the flue is maintained, flue gases cannot escape.

Some people will cover the barometric with foil or pull it off and cap the T in warm weather. I've never had to do either.

Lightning wrote: My speculation is that this lower pressure moves the neutral pressure plane higher. That being said, the lower pressure in the house would encourage cold air infiltration but up higher it would inhibit warm air from escaping. This concludes to me that half of the air going up the chimney is additional air infiltration. The other half is air that would infiltrate whether the stove is there or not.
But since the stove is there and it is creating negative pressure in the house, the other half of that air is air that couldn't escape above the neutral pressure plane.

What?????????? Elvis has left the building.

Rev. Larry

blrman07 wrote:What?????????? Elvis has left the building.

Rev. Larry

I know right??
I'm gonna take a little break and come back to this later..

Lightning wrote:Given the chimney is drawing air out of the house and all of that air is replaced by air infiltration from outside.
Also given, the air going out of the chimney should help create lower pressure in the house.

My speculation is that this lower pressure moves the neutral pressure plane higher. That being said, the lower pressure in the house would encourage cold air infiltration but up higher it would inhibit warm air from escaping. This concludes to me that half of the air going up the chimney is additional air infiltration. The other half is air that would infiltrate whether the stove is there or not.
But since the stove is there and it is creating negative pressure in the house, the other half of that air is air that couldn't escape above the neutral pressure plane.

Maybe I need a vacation.

Regarding the section of the quoted statement above that I have bold highlighted: If the stove (boiler/furnace) is in the basement, and the basement is naturally the lowest pressure zone in the house to begin with, and the chimney is drawing pressure away from what is already the lowest pressure zone in the house, the chimney is thereby creating a condition of even lower pressure at the basement level. Since energy can only move from a higher state to a lower state, that should tend to move the neutral pressure plane of the home lower, as pressure from above flows downward to fill the pressure void that the chimney is creating below. The lowered pressure in the basement as a consequence of chimney draft would also make for more infiltration via outside air into the basement level, where infiltration is already at its highest to begin with. Energy (heat) leaves a home primarily from the higher pressure levels residing above the neutral pressure plane, and enters a home at the low pressure level below the neutral pressure plane.

What any of this has to do with determining how much heat goes out of a home via a barometric damper vs. via an MPD remains unclear. Baro or MPD, the pressure differentials in a home will reach a tenuous state of equilibrium that is continually going to be in flux, with the homes neutral plane continually moving upward and downward to some degree as energy levels inside and outside of the home change. I can only bring question to the conclusion in the highlighted section.

I think I found some good information on this debacle. Have a look.
It says an active chimney will raise the NPP..

http://books.google.com/books?id=Eq1OqmBjSvYC&pg= ... ey&f=false

It may seem silly but this it quite a Revelation to me.. Since I assumed that all the air the furnace uses for combustion and baro drafting would be additional cold air infiltration.. But from where I'm standing that's not the case. The NPP is elevated due to the evacuation of air by the chimney. This means less air is leaving the house at the top AND instead that air is being used by the chimney and only part of the air that the chimney is taking is being replaced by additional air infiltration.

Where's ma beer...