The heating point cannot be overstated and I want to put a shape on it for anyone reading.
Old stone building, high ceilings, single glazing, electric heaters because there was no central system. My summer utility bill and my January utility bill were not in the same category of number. It was not a percentage increase, it was a different kind of expense that simply had not existed for the first five months.
What I would tell anyone: before signing anything for more than three months, ask what the building is heated with and ask the previous tenant - not the landlord: what the coldest month cost. Landlords answer that question optimistically and are not really lying, because they are usually quoting a mild year.
Also: a flat that is cheap because it is cold is not cheap. It is a bill deferred to January.