https://www.energyvanguard.com/blog/the-3-rules-of-air-leakage-plus-a-bonus/ Building science knowledge, HVAC design, & fun Tue, 31 Aug 2021 11:19:41 +0000 hourly 1 https://wordpress.org/?v=6.6.2 https://www.energyvanguard.com/blog/the-3-rules-of-air-leakage-plus-a-bonus/#comment-4122 Thu, 31 May 2012 01:34:39 +0000 http://energyvanguard.flywheelsites.com/?blog_post=the-3-rules-of-air-leakage-plus-a-bonus#comment-4122 Michael:
Michael: Touché. You are of course correct, and I’ve changed the title to remove the offending word, ‘immutable.’ (I went ahead and changed ‘laws’ to ‘rules,’ too.) I had reservations when I put it there and should have heeded them.  
 
I don’t care to go back into that whole stack effect diversion we had a few months ago (on GBA especially), but as you state in your comment, the barometric pressure is irrelevant to this discussion since it’s balanced by the weight of the air and cancels itself out. 
 
Anyway, thanks for the clarifications and for keeping me honest. I guess I have a tendency to oversimplify sometimes, so it’s good to get called on it when I do.

]]> https://www.energyvanguard.com/blog/the-3-rules-of-air-leakage-plus-a-bonus/#comment-4121 Thu, 31 May 2012 00:34:50 +0000 http://energyvanguard.flywheelsites.com/?blog_post=the-3-rules-of-air-leakage-plus-a-bonus#comment-4121 immutable? sort of…&amp
immutable? sort of… 
 
Law 1 is certainly true, but your example at the end is misleading I think.  
“When you turn on an exhaust fan in a bathroom or kitchen, you’re intentionally sending conditioned air to the outside. Each cubic foot that leaves is matched by a cubic foot of unconditioned air leaking in somewhere”. 
 
I read this statement to mean that the 50 CFM exhaust fan increases the infiltration rate by 50 CFM. But for typical existing homes in mid winter, when a 50 CFM exhaust fan only adds about 25 CFM to the total infiltration rate. The other 25 CFM comes from reducing the rate of flow out through the exfiltrating leaks. You only get 1 CFM of added infiltration per fan CFM when the fan is more than twice the natural leakage rate. 
 
Your law # 2 is not actually technically correct — you are neglecting height/gravity. There is about a 25 pa pressure difference between the air at the floor and ceiling of an 8 foot high room. The weight of the air balances (and actually creates) the pressure difference and so there is no flow from the floor to the ceiling. 
 
Your bonus description isn’t really completely accurate either. It would be more more accurate to say it takes all paths in inverse proportion to their resistances.  
 
sorry to nit pick, but immutable is strong language 😉

]]> https://www.energyvanguard.com/blog/the-3-rules-of-air-leakage-plus-a-bonus/#comment-4120 Tue, 29 May 2012 22:13:07 +0000 http://energyvanguard.flywheelsites.com/?blog_post=the-3-rules-of-air-leakage-plus-a-bonus#comment-4120 Attic ventilators are also
Attic ventilators are also known to depressurize combustion zones and cause backdrafting. Just ask Jom Fitz. who turned it on while we were testing a furnace. Mucho CO in the face

]]> https://www.energyvanguard.com/blog/the-3-rules-of-air-leakage-plus-a-bonus/#comment-4119 Tue, 29 May 2012 21:36:06 +0000 http://energyvanguard.flywheelsites.com/?blog_post=the-3-rules-of-air-leakage-plus-a-bonus#comment-4119 Mark, a pair of fans would
Mark, a pair of fans would cost twice as much and use double the energy, with very little marginal benefit. Upgrading to ECM motors and more intelligent controls would indeed improve performance, but such a system would be be very expensive compared to the benefit. In any case, that money would be better spent on air sealing the ceiling and additional insulation.

]]> https://www.energyvanguard.com/blog/the-3-rules-of-air-leakage-plus-a-bonus/#comment-4118 Tue, 29 May 2012 21:15:51 +0000 http://energyvanguard.flywheelsites.com/?blog_post=the-3-rules-of-air-leakage-plus-a-bonus#comment-4118 M. Johnson
M. Johnson: Even if power attic ventilators don’t suck air out of the house, that doesn’t mean they’re not a problem. If you do a great job air-sealing your ceiling and then install two fans as you describe, you’re still using excess energy, even with efficient motors. Passive ventilation works just fine.

]]> https://www.energyvanguard.com/blog/the-3-rules-of-air-leakage-plus-a-bonus/#comment-4117 Tue, 29 May 2012 20:52:26 +0000 http://energyvanguard.flywheelsites.com/?blog_post=the-3-rules-of-air-leakage-plus-a-bonus#comment-4117 Powered attic ventilators
Powered attic ventilators would hardly be the house-suck travesty people say they are, if installed in pairs where one blows in, one blows out. Nobody seems to grasp this. 
 
Then it would be merely a matter of energy (high) vs. benefit (small). Or cost vs. benefit. There ARE such things as low energy motors and more intelligent controls, but nobody seems to have applied that idea to the problem either.

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