[Greenbuilding] insulation vs. air sealing

nick pine nick at early.com
Fri Sep 24 15:48:43 CDT 2010

> The increased insulation is creating a larger temperature difference 
> between the living space and the attic. This increases the stack effect, 
> and increases the pressure at that boundary.  This causes MORE air to go 
> up through those holes (and the money to heat it as well).

More attic insulation will decrease the winter attic temp and DECREASE the 
stack effect flow.

More house insulation won't make any difference, given a thermostat.

Reducing the air changes per hour from 2 to 0.5 in a 2400 ft^2 house will 
lower the air leakage by 1.5x2400x8/60 = 480 cfm and lower the house 
conductance by about 480 cfm and save about 24hx4805x480 = 55 million 
Btu/year in NYC's 4805 HDD(F) climate, about 550 therms/year of natural gas, 
about $1100 at $2/therm. Adding R20 insulation to a 2400 ft^2 R20 attic will 
lower the house conductance by 2400(1/20-1/40) = 60, saving 24hx4805x60/100K 
= 69 therms worth $138.


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