window infiltration

Unknown

That software uses U-factors directly. The factor for the windows and walls can be typed in directly. The square feet (or inches, in some cases; be careful) works with the U factors to give the losses.

Infiltration is a whole different number, and the single LARGEST factor in the program. Windows and doors are the second largest. Be very careful with the infiltration numbers.

Noel

Tim_41

window infiltration

I noticed a sticker on a new window that gave the "U-Factor" of the window. It is .35 .. Would this be what we use for the window infiltration number on the slant fin express heat loss?
Thanks
TimS

Brad White

U-Factor

Hi Tim-

No, the u-factor is a measure of conductance (transmission), not infiltration (air leakage). A 0.35 u-factor at -10 outside and 70 F. inside will transmit 28 BTUH per SF.

Infiltration as far as the Slant-Fin program is concerned I cannot say, but I do use a variety of means to calculate that variable.

Keep in mind that published glass u-factors are "center of glass" and are larger (less efficient) when averaged over the entire assembly including edges. For example, a multi-pane window will have more perimeter per SF of glass area and thus be less efficient than a single larger pane. Absent better information, (such as an actual whole window assembly number from the manufacturer), I would add about 15%-20%.

Tim_41

Thanks

for the info Brad.