arachides= > APXIDIA
What so many homowners don't understand is that heating systems ares sized with a heat ouptut according to design temeratures. (scheduke "J" is it?) At XYZ outside temperature we want it to maintain an ABC indoor temperature.
So when abnormal outdoor temeratures prevail, many heating systems struggle to keep up. In the old days systems were pruposely oversized (energy was inexpesnve). Nowadays when properly sized, when such extreme cold comes, they simply won't keep up. Avoiding a night-time setback in temepratures may help somewhat on extremely cold or windy nights.
Of course those heating systems (steam or hydronic [i.e. hot -water]) that also produce hot water for the taps have some extra cacity that was designed-in for that purpose. Then, of course your showers may be cooler than normal, and the heating circulators may stop to ensure hot water at the taps.
Personall if I get a house again, I'm going to get a gravity gas-fired unit heater or wall-furnace (as seen in California) that does not depend on electricity to supplemment the main heatiung system. Will have heat during blackout-outs, lack of oil-supply and extra cacity when it's so cold your "arachides" are up in your abdomen.