Points out that measured values of the conductive heat loss factor of a building are often significantly smaller than the calculated design value. Presents a study which shows that the coheating method generally underestimates the heat loss factor due to neglect of heat discharge from thermal masses during the night, while the classic calculation (UAcl = UAo+MCp) generally overestimates the heat loss factor due to neglect of air infiltration heat recovery.

KEYWORDS: year 1995, Calculating, heat loss, buildings, accuracy, measuring