Data are presented from nighttime measurements of the net heat flow through several types of skylights. A well-known thermal test facility was reconfigured to measure the net heat flow through the bottom of a skylight/light well combination. Use of these data to determine the U-factor of the skylight is considerably more complicated than the analogous problem of a vertical fenestration contained in a test mask. Correction of the data for heat flow through the skylight well surfaces and evidence for the nature of the heat transfer between the skylight and the bottom of the well is discussed. The resulting measured U-factors are presented and compared with calculations using the WINDOW4 and THERM programs.

Units: SI