When we bought this house, we installed a gas heater that was pretty much as efficient as they came back then (14 years ago), and since then we've successively added insulation as we've renovated/improved. Because it's a townhouse we don't have to worry about 2 sides of the building, and because it's only 5 m wide the exposed walls are relatively small.

Our thermostat is set to 18 °C daytime/15 °C night.

The fact is that what we're experiencing right now is a top-down disaster. -Paul Krugman