02 Dec COLD WEATHER AND SHABBAT: A PRACTICAL HALACHIC GUIDE TO HOME HEATING

During the cold
winter days, one must
ensure before Shabbat
that the heating is set
to the proper
temperature. If he
forgot to set it or there is another reason the
house feels cold, he may not turn on the heat
on Shabbat.
However, if the temperature reaches the
freezing point, it is permitted to ask a non-Jew
to turn on the heat due to the concern for
danger. Even when it is not that cold, it is still
permitted to ask a non-Jew to turn on the heat
if there are small children, elderly individuals,
or someone who is ill in the house (S.A siman
176, 5).
If a non-Jew turned on the heat when it wasn’t
very cold, there is a distinction between two
cases:
1. The heating system was already on, and
the non-Jew merely raised the temperature.
In this case, one may benefit from the
additional heat, since the system was already
operating (M.B. 34).
2. The heating system was completely off,
and the non-Jew turned it on.
In this situation, one may not benefit from the
heat, since the melachah was done entirely for
the Jew (Igrot Moshe Y.D. 3, 47).

Radiator Valve:
A hot-water (hydronic) heating system works
by heating water in a boiler and circulating it
through pipes to radiators or baseboard units
throughout the home, where the heated water
warms the metal and gently radiates heat into
the rooms.
If the house feels cold, one should not open the
radiator valve on Shabbat, since doing so
allows cold water to enter the system and heat
up. Allowing cold water to flow in and be
boiled constitutes the prohibition of cooking.
This prohibition applies only on Shabbat; on
Yom Tov it is permitted, since cooking is
allowed on Yom Tov.
If the room is cold and there is a need to heat
the house, it is permitted to ask a non-Jew to
open the valves. In this case, the water entering
the system was previously heated and later
cooled down. Whether reheating such water is
prohibited is a dispute among the Rishonim.
Although the Shulchan Aruch rules stringently
that reheating it is not permitted, since it
remains a matter of halachic debate, one may
rely on the lenient view when the action is
performed by a non-Jew.
If the room becomes too hot and one wishes to
close the valve, the halacha depends on the
temperature of the water already circulating in
the system:
• If the water has already reached the

temperature of yad soledet bo, closing the
valve is permitted. At that point no further
Shabbat prohibition occurs, since the water is
already considered fully cooked.
• However, if the water has not yet reached the
level of yad soledet bo, closing the valve
would cause the water to heat faster, since the
circulation path becomes shorter and the water
travels less. This accelerates the cooking
process and is therefore a violation of the
prohibition of cooking on Shabbat.
Forced-air systems pose no halachic concern
when merely opening or closing the air vents,
since we do not consider these actions
significant enough to make the system work
harder, turn on sooner, or shut off earlier, and
the primary prohibition remains only on
adjusting the thermostat itself, which directly
controls the electric activation of the furnace.
Thermostats:
• If the heating system operates with an electric
thermostat, one may not adjust it on Shabbat at
all, since any change involves the use of
electricity.
• If it is a mechanical thermostat, some
authorities permit lowering the temperature
only while the system is off, before the
thermostat triggers the heating cycle. Lowering
it merely delays the next heating cycle and
does not cause the system to turn on. However,
one may not raise the temperature, since doing

so may cause the system to activate sooner,
which would be considered causing it to turn
on.
Oil-filled and electric radiators:
Fully enclosed, thermostat-free oil-filled
radiators raise no unique halachic issues
beyond the basic prohibition on using
electricity: they may not be turned on or off or
adjusted on Shabbat, but if activated before
Shabbat one may fully benefit from them, and
their internal heating and circulation pose no
concern. The same applies to simple electric
portable heaters that lack thermostats or
adjustable settings—once they are turned on
before Shabbat, one may enjoy their heat
throughout Shabbat, though turning them on
or off or modifying any control remains
prohibited.
These heaters are muktzeh on Shabbat and
may not be moved for any reason, unless there
is a danger of fire or another safety issue. The
reason they are muktzeh is that the heating
elements inside the radiator become red hot
and are considered fire, while the radiator
itself serves as the base (בסיס (for that fire.