Dear Rabbi, What is the difference between adding wood to a woodheater or fireplace on Shabbat, if you have the wood already stacked by the stove or chimney, for example in former centuries in the icy cold of Lithuania or Russia, and in today’s modern homes where the electricity and gas continue to keep us cozy and warm. This automatic feeding of fuel and automatic thermostat seems not to be different than adding wood to your primary source of not freezing to death in cold countries. We live in the countryside in France and have had electricity failures in the winter hurricaine (maybe the only real hurricaine in 3000 years here!) of 1999 for over a week. The woodstove never stopped during that period of freezing winds and ice storms. It would have been impossible to have a family stay in such a situation. I am not speaking about cooking on Shabbat or an amusing campfire. I am talking about not having the toilets freeze and the home barely getting above freezing and kids catching phneumonia, G-d forbid. Jews lived like just until very recently.
Work done before the onset of shabbat is permitted even if the results of the pre-shabbat work are felt on shabbat (for example: shabbat candles lit before shabbat continue to burn into Shabbat).In contrast, the Torah prohibits doing one of the 39 labors forbidden on shabbat itself even if the results could have been achieved by pre-shabbat labor. Adding wood to a fireplace on shabbat violates shabbat as this is one of the 39 prohibited labors. Someone with an electric or gas heater who sets it before shabbat is doing nothing at all on shabbat (theoretically he could sleep throughout shabbat and the heater would work in exactly the same way). One cannot violate shabbat on Friday. The Sadducees interpreted the verse that prohibits lighting a fire on shabbat to be a prohibition on having a fire burning on shabbat. Our disagreement with them is that we allow a fire to burn on shabbat if we do nothing on shabbat itself. If you feel that another hurricane is on the way, perhaps you should get a gas heater or a kerosene heater that you can light on Friday and it will continue without further intervention on shabbat.