We are forgetting that it’s incredibly important for a house to breath. It’s necessary to vent out a home. In a perfect world keeping all the heat we pump into our house and never wasting it would be amazing, however that means we are also keeping all the moisture, microbes, allergens, toxic cleaning agents etc. Natural ventilation is a must.
You are correct. In a nutshell, the taller chimney drafts better because of the greater difference between the outside atmospheric pressure in relation to the height of the heated column.
We're used to feeling fluid pressure when we dive under water. As divers and snorkelers know well, the pressure adds up quickly as you accumulate a thicker column of water above you (i.e. as you dive deeper). We're less use to thinking about air as a fluid, but it behaves as a fluid and we notice the difference in atmospheric pressure changes when we go into the mountains, fly in planes, etc. Because it's a less dense fluid, it takes more height variation to accumulate a noticeable difference.
That is correct. All combustion appliances that aren’t completely sealed must have adequate makeup air under worst case depressurization. A worst case depressurization test should be performed on any home that has undergone significant changes regarding air tightness - particularly weatherization.
So yes, if your house was the same temperature as outside, there would be no stack effect, as the air densities would be the same. And yes, if you cool your house in the summer, the stack effect can reverse.
Rigid foam board is common as both foundation & underslab insulation. New construction offers the best chance at dealing with radon - in terms of both performance & economics. Carry the ground vapor retarder all the way out past the footer rather than ending it at the slab & ideally tie it into the foundation wall waterproofing. Install the perforated collection pipe under the slab. This pipe is inexpensive & gives the option to depressurize under the slab (with a radon fan) if necessary.
Hot air is less dense than cold air, and we're used to thinking about this as "heat rises". Really, a less dense fluid will rise when immersed in a sea of more dense fluid. This sea is our atmosphere, and we take advantage of that effect to use wood stoves, hot air balloons, etc.
Stack effect pressures are very, very small in terms of our perceptions. A few pascals, a fraction of a fraction an inch water column. Nevertheless, the same phenomenon exists with our fixed, not-so-hot air balloons (our houses). A taller house (or chimney) develops a stronger stack effect (or draft) because it creates a taller column of warm to hot buoyant air (i.e. less dense) relative to the outside cold air (i.e. more dense).
So because I've solved backdraft dangers with "direct vent" I'm more concerned about dew points, condensation, frost (like we see in the attic here), meeting of frost, and evaporation of that melted water before it causes damage in "walls, ceilings, attics. Considering radon...why not spray on concrete sealer silicate? Or a better idea...rigid closed cell foam under cement slab and outside basement walls.
The taller you go, the more you are cheating gravity of the pressure it would exert on the ground if you didn't insist on heating your house. If one story is enough to produce X amount of pressure difference between inside and outside, then two stories will be 2X in pressure difference. The taller you go, the more of a "deficit" of pressure you create that would be exerted if the air was as dense as the ambient air.
Seal from the top down. Ok. Great. But this isn't a practical "total solution". Are we not going to have the same problem when we have bathroom fans on, heck, even when the exhaust fans are off there is still tones of air leakage. Danger of backdraft is why we need direct vent to all combustion appliances.
We are forgetting that it’s incredibly important for a house to breath. It’s necessary to vent out a home. In a perfect world keeping all the heat we pump into our house and never wasting it would be amazing, however that means we are also keeping all the moisture, microbes, allergens, toxic cleaning agents etc. Natural ventilation is a must.
this was an awesome, very clear explanation and demonstration. thank you so much.
You are correct. In a nutshell, the taller chimney drafts better because of the greater difference between the outside atmospheric pressure in relation to the height of the heated column.
We're used to feeling fluid pressure when we dive under water. As divers and snorkelers know well, the pressure adds up quickly as you accumulate a thicker column of water above you (i.e. as you dive deeper). We're less use to thinking about air as a fluid, but it behaves as a fluid and we notice the difference in atmospheric pressure changes when we go into the mountains, fly in planes, etc. Because it's a less dense fluid, it takes more height variation to accumulate a noticeable difference.
That is correct. All combustion appliances that aren’t completely sealed must have adequate makeup air under worst case depressurization. A worst case depressurization test should be performed on any home that has undergone significant changes regarding air tightness - particularly weatherization.
So yes, if your house was the same temperature as outside, there would be no stack effect, as the air densities would be the same. And yes, if you cool your house in the summer, the stack effect can reverse.
Rigid foam board is common as both foundation & underslab insulation. New construction offers the best chance at dealing with radon - in terms of both performance & economics. Carry the ground vapor retarder all the way out past the footer rather than ending it at the slab & ideally tie it into the foundation wall waterproofing. Install the perforated collection pipe under the slab. This pipe is inexpensive & gives the option to depressurize under the slab (with a radon fan) if necessary.
Hot air is less dense than cold air, and we're used to thinking about this as "heat rises". Really, a less dense fluid will rise when immersed in a sea of more dense fluid. This sea is our atmosphere, and we take advantage of that effect to use wood stoves, hot air balloons, etc.
Stack effect pressures are very, very small in terms of our perceptions. A few pascals, a fraction of a fraction an inch water column. Nevertheless, the same phenomenon exists with our fixed, not-so-hot air balloons (our houses). A taller house (or chimney) develops a stronger stack effect (or draft) because it creates a taller column of warm to hot buoyant air (i.e. less dense) relative to the outside cold air (i.e. more dense).
Thanks for your sharing
So because I've solved backdraft dangers with "direct vent" I'm more concerned about dew points, condensation, frost (like we see in the attic here), meeting of frost, and evaporation of that melted water before it causes damage in "walls, ceilings, attics. Considering radon...why not spray on concrete sealer silicate? Or a better idea...rigid closed cell foam under cement slab and outside basement walls.
The taller you go, the more you are cheating gravity of the pressure it would exert on the ground if you didn't insist on heating your house. If one story is enough to produce X amount of pressure difference between inside and outside, then two stories will be 2X in pressure difference. The taller you go, the more of a "deficit" of pressure you create that would be exerted if the air was as dense as the ambient air.
you get it. something most people in the industry have zero knowledge of
Seal from the top down. Ok. Great. But this isn't a practical "total solution". Are we not going to have the same problem when we have bathroom fans on, heck, even when the exhaust fans are off there is still tones of air leakage. Danger of backdraft is why we need direct vent to all combustion appliances.