Quote:
Originally Posted by Daox
To go along with adding the soffit vents I'm looking at adding some insulation to the attic of the house. It currently has 6" of fiberglass insualtion which is supposidly around an R-19. The recommended R value for my area (Wisconsin) is R-49! So, I was thinking of blowing in some cellulose on top of the fiberglass to boost it up to R-49. However, I'm also wondering if it would be worthwhile to go a bit higher than R-49? Does anyone have any info that compares added insulation to energy savings?
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Doax,as you probably know,your heat transfer coefficient is the reciprocal of your R-factor.It's kinda like the drag coefficient,as in this case,for your ceiling.So the lower the number,the less drag(on your pocketbook).Going from R-19 to R-49 shifts your U-value (like Cd) from 0.0526,to 0.0204.-------------------------- Say on a hot summer day,and the attic was at 110-degrees,and you were trying to keep the house at 78-degrees inside,then the heat transfer you have now would be your delta-T ( 110-78 degrees) times your U-value(0.0526),times the area of the ceiling.So say for 1000 square-feet,you'd have [ 32 (degrees) times 0.0526,times 1000 (square-feet) = 1683 Btu/hour entering the house through the ceiling/per 1000 square feet.-------------------------------------- If you go up there and blow the cellulose,and get the R-factor up to 49,for the same design conditions,your new cooling load would drop to 1030 Btu/hour,for each 1000 ft.Almost a 39% load reduction at the ceiling.--------------------------------------- You could throw in some numbers for the winter and calculate your heating load as the ceiling loses your precious heat.Say at 30-degrees in the attic,and trying to maintain 68-degrees as recommended by utility companies,adding the insulation would save you 1225 Btu/hr.