Chapter 23
Housekeeping and Use of Domestic Facilities on Shabbath and Yom Tov.
CENTRAL HEATING
20.a. The thermostat which regulates a central-heating system may be turned to a lower marking on Shabbath or Yom Tov only when the system is not operating.
20.b. 1) It is forbidden, both on Shabbath and on Yom Tov, to turn the thermostat to a higher marking while it is preventing the system from operating.
2) Turning up the thermostat while the system is operating
a) is permitted on Yom Tov, but
b) should be avoided on Shabbath.
21.a. There is nothing wrong with opening and closing the doors or windows of a centrally heated apartment or house on Shabbath or Yom Tov.
21.b. That is to say, one need not worry that one will thereby accelerate the ignition or extinction of the thermostatically operated heating system.
