Absolutely, finny.
During the Winter months (well, Autumn & Spring as well) we can easily double our fuel consumption. Our 5kW heater can use up to 0.5L/H if it's really cold outside.
It doesn't help that we have an electrics-only boat with a 10kW genny to power it, unless we can plug into leccy.
(which is probably another reason that we like to keep our motive-motor's appetite down!).