- #1
Naty1
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I'm in the process of replacing 1970's double hung wood windows with modern high efficiency vinyl windows...this is awfully long but I thought others might be able to use the methodology for their own homes if considering new windows...the 30% government tax cedit, up to $1,500 runs out the end of this year (2010) ...together with a sale of 10% or 20% off and doing some window installations yourself, it's not a crazy investment.
Edit add on:
Heat is transferred by conduction,convection and radiation. My calculations below cover conduction (via U and R factors)...what I have been unable to account for are heat losses due to convection (air infilitration) and radiation.
I'd like to know the heat losses thru my windows...and the cost of that lost heat...the heating side is easy as I know my furnace size, efficiency and the cost of a therm of gas...
When I calculate approximate total heat losses for my home based on an R of about 3.3 (per sqft per degree Fahrenheit temp difference) for new windows, an R 13 for walls, an R 5 for floors over a basement and an R 30 for ceilings, my total heat loss in BTU's is too small. Door losses seem negligible but I guess I should estimate them with a R of about 2..I did not do that the first time around...it's small...
I assume I am not accounting for quite a bit of heat loss due to air infiltration...I seem to recall seeing some figures many years ago associated with 15 mph winds...can't find anything like that now...
Anybody have a reference online or a typical figure/factor for air infiltration I can use?? ...How is this calculation done?
My interest is in trying to estimate how much heat is lost via my windows versus walls,ceilings, and floor. I know I'll not get back my window replacement costs anytime soon, but I would like to know the heat loss via windows...With walls at R13 and double pane low E and argon glass R is about 3.3, likely window loss per sq ft is 13/3.3 or about four times as much per sqft as walls...but likely air infiltration would boost that to five maybe six times overall...?
My window area is about 325 sq ft (U is 0.3), walls w/o windows about 1030(U is 1/13), floor and ceiling about 1380 sqft each (U is 1/30, and 1/5) respectively so losses using this single factor are per degree temperature difference inside vs outside:
Heat loss per degree temp difference
325 x 0.3 is 98 BTU/Hr (windows)
1030/13 is 80 BTU/Hr (walls)
1380/30 is 46 BTU/Hr (ceiling)
1380/5 is 276 BTU/Hr (floor)
So on a 70 degree basis inside, say 10 degrees outside, 60 degree basement temp:
Total heat loss @ 60 degree inside/outside temp diff:
98 x 60 is 5880 BTU/Hr (windows)
80 x 60 is 4800 BTU/Hr (walls)
46 x 60 is 2400 BTU/Hr (ceiling)
276x 10 is 2760 BTU/Hr (floor)
Total: 15,840 BTU/Hr my guess is this should be about 30K to 40K BTU/Hr...
Also makes me wonder why I have 100,000 BTU furnace at 96% efficiency...seems like over kill even if 20 below zero...such a temp would boost my total heat loss to 90/60 x 15,840BTU or about 23,760 BTU...still awfully small...
Edit add on:
Heat is transferred by conduction,convection and radiation. My calculations below cover conduction (via U and R factors)...what I have been unable to account for are heat losses due to convection (air infilitration) and radiation.
I'd like to know the heat losses thru my windows...and the cost of that lost heat...the heating side is easy as I know my furnace size, efficiency and the cost of a therm of gas...
When I calculate approximate total heat losses for my home based on an R of about 3.3 (per sqft per degree Fahrenheit temp difference) for new windows, an R 13 for walls, an R 5 for floors over a basement and an R 30 for ceilings, my total heat loss in BTU's is too small. Door losses seem negligible but I guess I should estimate them with a R of about 2..I did not do that the first time around...it's small...
I assume I am not accounting for quite a bit of heat loss due to air infiltration...I seem to recall seeing some figures many years ago associated with 15 mph winds...can't find anything like that now...
Anybody have a reference online or a typical figure/factor for air infiltration I can use?? ...How is this calculation done?
My interest is in trying to estimate how much heat is lost via my windows versus walls,ceilings, and floor. I know I'll not get back my window replacement costs anytime soon, but I would like to know the heat loss via windows...With walls at R13 and double pane low E and argon glass R is about 3.3, likely window loss per sq ft is 13/3.3 or about four times as much per sqft as walls...but likely air infiltration would boost that to five maybe six times overall...?
My window area is about 325 sq ft (U is 0.3), walls w/o windows about 1030(U is 1/13), floor and ceiling about 1380 sqft each (U is 1/30, and 1/5) respectively so losses using this single factor are per degree temperature difference inside vs outside:
Heat loss per degree temp difference
325 x 0.3 is 98 BTU/Hr (windows)
1030/13 is 80 BTU/Hr (walls)
1380/30 is 46 BTU/Hr (ceiling)
1380/5 is 276 BTU/Hr (floor)
So on a 70 degree basis inside, say 10 degrees outside, 60 degree basement temp:
Total heat loss @ 60 degree inside/outside temp diff:
98 x 60 is 5880 BTU/Hr (windows)
80 x 60 is 4800 BTU/Hr (walls)
46 x 60 is 2400 BTU/Hr (ceiling)
276x 10 is 2760 BTU/Hr (floor)
Total: 15,840 BTU/Hr my guess is this should be about 30K to 40K BTU/Hr...
Also makes me wonder why I have 100,000 BTU furnace at 96% efficiency...seems like over kill even if 20 below zero...such a temp would boost my total heat loss to 90/60 x 15,840BTU or about 23,760 BTU...still awfully small...
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