The U Factor measures the rate of heat transfer or {HEAD ~ loss} through {TAIL ~ a window} as laid down by the National Fenestration Rating Council 
through
The U Factor measures the rate of heat transfer or { HEAD ~ loss } through { TAIL ~ a window } as laid down by the National Fenestration Rating Council
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH