Where night set-back is a viable option, a secondary
question is whether to turn the system off or simply
turn the thermostat setpoint down (or up). This is not a
question which can be answered simply. The answer is
dependent on the length of time the system will be setback
and how much temperature variation will occur if
the system is turned off. The question of whether it is
even advisable to turn the system off is also influenced
by humidification and pressurization requirements, air
quality concerns, etc. See §10.5,1.