Barometric Dampers and Cold Air Infiltration
- Lightning
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It's thought by some that baro's introduce an excessive amount of cold air infiltration into the home. I mean, the air that is going into the baro damper and going up the chimney has to come from somewhere right? and you are correct to say that all of it ultimately comes from outside. But how much of the air that the baro is sucking up is actually additional air infiltration? I've started this thread to demonstrate that only part of the air that the baro and stove use is "additional" air infiltration. Only part of it is additional, not all. I can see you scratching your head from here.. How can only part of it be additional and not all?? Well, lets look at it from a "pressure's" point of view.
During the cold months, a house develops a neutral pressure plane. What the hell is that? It's a horizontal plane in the house where the pressure in the house exactly equals pressure outside and it normally resides at about the mid section of the home. Above this plane, the pressure is positive (as compared to outside) and increases as you get closer to the ceiling. Below this plane, the pressure is negative (as compared to outside) and gets stronger as you get closer to the basement floor.. Like in the sketch below.
Ok, now lets look at cold air infiltration and warm air ex-filtration. Since now there are pressure differences at the ceiling and at the floor, air will try to find it's way out where the pressure is positive and will try to find it's way in where it's negative. This causes air turn over in the house. Air turn over of the home actually happens several times a day and is needed. If the air in your home was never replaced by fresh air outside, it would quickly become an unhealthy environment. Air infiltration is actually a good thing, but excessive infiltration can cause cold spots and run up the heating bill. Keep in mind that the air leaving the home at the ceiling equals the air coming in at the floor (in the house above). This is important in this demonstration.
Ok, now we introduce a stove and baro that are pumping air out of the house at the same time natural air turn over is already occurring due to stack effect of the house. This part gets a little hairy. Since we now have an appliance pumping air out of the house, this effects the position of the neutral pressure plane by raising it slightly, as demonstrated in the sketch below.
Since pressure is the soul motivator for infiltration and ex-filtration, it's easy now to see that a little less air is leaving the house at the ceiling and a little more air is entering at the floor. How can more air come in than is leaving? It's not, they are still equal. The unaccounted for air that isn't leaving at the ceiling is being re-routed thru the baro and stove. The baro and stove consume X number of cubic feet per minute of air in the house. In my hypothetical home, air has the same resistance leaving at the ceiling as it does entering at the floor. Half of variable X comes from additional infiltration, the other half is air that would have left at the ceiling but didn't because the positive pressure is weaker there due to the lifting of the neutral pressure plane..
This is what goes on in my head anyways..
During the cold months, a house develops a neutral pressure plane. What the hell is that? It's a horizontal plane in the house where the pressure in the house exactly equals pressure outside and it normally resides at about the mid section of the home. Above this plane, the pressure is positive (as compared to outside) and increases as you get closer to the ceiling. Below this plane, the pressure is negative (as compared to outside) and gets stronger as you get closer to the basement floor.. Like in the sketch below.
Ok, now lets look at cold air infiltration and warm air ex-filtration. Since now there are pressure differences at the ceiling and at the floor, air will try to find it's way out where the pressure is positive and will try to find it's way in where it's negative. This causes air turn over in the house. Air turn over of the home actually happens several times a day and is needed. If the air in your home was never replaced by fresh air outside, it would quickly become an unhealthy environment. Air infiltration is actually a good thing, but excessive infiltration can cause cold spots and run up the heating bill. Keep in mind that the air leaving the home at the ceiling equals the air coming in at the floor (in the house above). This is important in this demonstration.
Ok, now we introduce a stove and baro that are pumping air out of the house at the same time natural air turn over is already occurring due to stack effect of the house. This part gets a little hairy. Since we now have an appliance pumping air out of the house, this effects the position of the neutral pressure plane by raising it slightly, as demonstrated in the sketch below.
Since pressure is the soul motivator for infiltration and ex-filtration, it's easy now to see that a little less air is leaving the house at the ceiling and a little more air is entering at the floor. How can more air come in than is leaving? It's not, they are still equal. The unaccounted for air that isn't leaving at the ceiling is being re-routed thru the baro and stove. The baro and stove consume X number of cubic feet per minute of air in the house. In my hypothetical home, air has the same resistance leaving at the ceiling as it does entering at the floor. Half of variable X comes from additional infiltration, the other half is air that would have left at the ceiling but didn't because the positive pressure is weaker there due to the lifting of the neutral pressure plane..
This is what goes on in my head anyways..
Last edited by Lightning on Tue. Feb. 24, 2015 3:13 am, edited 1 time in total.
- northernmainecoal
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Does a baro really change the amount of air infiltration at all? Assuming there isn't a mpd, and no baro I'm getting -.01 of WC. All of that air is passing through the firebed and out the chimney. With a baro set at .05 half of the air is being pulled through the fire bed. Is more than -.05 entering the baro?
- mozz
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I've come to the conclusion, that when your in-laws are saying goodbye, standing next to your open door, for 5 minutes, negates any and all barometric losses for 4 years.
There is a lot of thinking that goes on to come up with sketches and stuff like that in a thread!!! That must be a power vent installation because I don't see a chimney on that house.
Same as northernmaine.....I always thought of it as X amount of vacuum in a chimney causing a certain volume of air to flow up that chimney. If there is no baro then all of that airflow comes through the stove. If there is a baro then a portion of it comes through the baro and a portion through the stove. It doesn't seem to me to add to the airflow just an alternative path to the already exiting air up the chimney.
and worse than the in-laws is when the teenager leaves a 1" gap when they are sure they closed the sliding door...... I thought having her carry in four 35lb buckets of coal was an even trade for the heat loss...it gave the coal vac a rest!
Same as northernmaine.....I always thought of it as X amount of vacuum in a chimney causing a certain volume of air to flow up that chimney. If there is no baro then all of that airflow comes through the stove. If there is a baro then a portion of it comes through the baro and a portion through the stove. It doesn't seem to me to add to the airflow just an alternative path to the already exiting air up the chimney.
and worse than the in-laws is when the teenager leaves a 1" gap when they are sure they closed the sliding door...... I thought having her carry in four 35lb buckets of coal was an even trade for the heat loss...it gave the coal vac a rest!
- windyhill4.2
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< That is what I would be doing if I worried & tried to figure out all the plane directions. Here is how our coal stove works to heat our house ~~~~~~~~ I put coal in ,take ashes out,the coal gets hot & burns into ashes,while this is going on the stove radiates heat into our house,the baro controls the over draft we would have with all the wind gusts we get here , we get warm ~~~~Problem solved. ~~~~~~~~~~~~~``` Lightning , I am not making fun of your science,it is interesting , I just thought that some folks would like to know how our stove & chimney work.
- Ky Speedracer
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Nice job explaining it bro!
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- coaledsweat
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I would think so, but it would be less infiltration not more. Without the baro, you would be sucking more air into the house but giving up heat from the applance while doing so requiring you to burn more coal and air to keep the house at the same temp.northernmainecoal wrote:Does a baro really change the amount of air infiltration at all?
- coaledsweat
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You should be able to close it up somewhat. The reason for the baro is to keep the chimney from siphoning off the heat your appliance is making. Without it the appliance and house will have to draw on more air and coal to maintain the heat.Ctyankee wrote:If you install a baro, do you have to open up the air intakes in order to keep the same firebox temperature?
- Lightning
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On a hand fed, yes. You will need to open the air intake to keep the same fire box temperature. A baro weakens the negative pressure in the fire box. So, if your fire box pressure is -.08 before the installation of a baro and then the baro is set for a pressure of -.04 when it's installed, a combustion air opening of the same size will draw less air. Less combustion air of course means the coal bed will burn slower and not as hot.Ctyankee wrote:If you install a baro, do you have to open up the air intakes in order to keep the same firebox temperature?
- Lightning
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If I'm interpreting your question right, you are wondering about air volume displacement of a combustion air opening with -.1 behind it compared to a baro AND combustion air volume displacement with both at -.05 behind them.northernmainecoal wrote:Does a baro really change the amount of air infiltration at all? Assuming there isn't a mpd, and no baro I'm getting -.01 of WC. All of that air is passing through the firebed and out the chimney. With a baro set at .05 half of the air is being pulled through the fire bed. Is more than -.05 entering the baro?
I believe that scenario #2 (the baro and combustion air opening with -.05) will move more volume of air out of the house and up the chimney. For the simple fact that the baro opening is so much bigger in relation to the combustion air opening.
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The baro on my hand fed stove enables me to control stove temp , not the wind. It's got quite a workout the last few weeks. Is it causing cold air infiltration ? Maybe, but as long as the Boss doesn't feel it . It doesn't matter.
- Lightning
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Another thing I want to add to the whole air infiltration/baro debacle.
As it gets colder outside, the stack effect in the house becomes even stronger yet causing even more infiltration and faster turn over of air in the house. As we stare at our baros agape during cold spells, it can be misinterpreted that the baro is the culprit for the additional cold drafts in the house when it really only amounts to a drop in the bucket.
In my mind as in the mind of many baro believers, the advantage of keeping a steady draft pressure on the appliance far outweighs the meager detriment of additional air infiltration it might cause.
As it gets colder outside, the stack effect in the house becomes even stronger yet causing even more infiltration and faster turn over of air in the house. As we stare at our baros agape during cold spells, it can be misinterpreted that the baro is the culprit for the additional cold drafts in the house when it really only amounts to a drop in the bucket.
In my mind as in the mind of many baro believers, the advantage of keeping a steady draft pressure on the appliance far outweighs the meager detriment of additional air infiltration it might cause.