Why is one room in my house always colder than the others?

Because heat loss and heat delivery are not distributed evenly around a house, and one room is usually losing more, receiving less, or both. Working through the possibilities in order saves a lot of guesswork.

Start with exposure. A room with more external walls loses more heat than one surrounded by other rooms — a corner room has two, a room above an unheated garage or a passage has a cold surface underneath as well. North-facing rooms get no solar gain. These are inherent, and the answer is more insulation rather than more heat.

Then check the heat going in. Radiators are commonly undersized for the room they were put in, especially after an extension or a change of use. A radiator that is cold at the bottom has a sludge build-up; cold at the top means trapped air and needs bleeding. If one radiator is cold while the rest of the system is hot, the system may need balancing — adjusting the lockshield valves so flow is not all going to the radiators nearest the boiler.

Air movement is the next suspect, and often the largest single factor. Draughts around a poorly fitting window or door, an unsealed loft hatch, gaps around pipework, or an open chimney can move more heat than any radiator upgrade will replace. Draught-proofing is cheap and usually the highest-return fix.

Finally, check for missing insulation. Thermal imaging, or simply feeling the walls on a cold day, often reveals a section of cavity wall that was never filled or loft insulation that stops short over one room.

A persistently cold room with damp or mould also needs the ventilation addressed, not just the heating.