People who live in an apartment can safely skip this tip, but otherwise think of that fireplace and chimney. Unused, open chimneys waste heat, letting expensive warm air out and cold air in.
King Charles has probably got chimney dampers on all his palace fireplaces, which can simply shut the chimney when the fireplace isn’t in use.
For the hoi poloi living in rented Victorian houses with an open fireplace in their bedroom though, chimney balloons are one solution – plastic bags which can be inflated and pushed up the chimney to block it – but are not recommended because they don’t fit well, allow lots of air through the gaps, and often deflate on their own and fall out. Fans of Tom Sharpe’s Porterhouse Blue will know of worse dangers (they used condoms filled with natural gas).
A better option which is more long-lasting, better fitting and more efficient, is a chimney draught stopper which doesn’t cost much more (£20), can be trimmed to shape and lasts much longer.