B
Backup heating
See Auxilliary heating.
Balance point
The outdoor temperature at which useful solar and internal gains equal the heat
loss; the building needs additional inputs of heat at outdoor temperatures below
the balance point and is free-running at temperatures above it.
Base temperature
A temperature datum taken as a base for the calculation of heating
degree days; for example, the setting on the main thermostat controlling
the heating appliances, or a volume-weighted mean
whole-house temperature or the balance point
temperature.
Black body
A (theoretical) perfect absorber and emitter of radiation with absorptance
and emissivity of 1.0 for all
wavelengths.