A house that is consistently cold despite the heating being on is both uncomfortable and expensive, as the heating system works harder to compensate for heat loss. Understanding the most common causes helps identify whether the solution is insulation, draught-proofing, heating system improvement, or a combination.

Insufficient Insulation

Heat loss through a poorly insulated house is continuous and substantial. The main heat loss pathways in a typical UK home are the roof (around 25 percent of heat loss in an uninsulated house), walls (around 33 percent), windows (around 10 percent), floors (around 15 percent), and draughts (around 17 percent). If loft insulation is absent or thin, installing 270mm of mineral wool is one of the most cost-effective improvements available and can make a significant difference to the thermal comfort of rooms below the loft.

Draughts

Cold air entering through gaps around doors, windows, floorboards, loft hatches, and letterboxes can make a well-heated room feel cold regardless of the boiler output. Draught-proofing is inexpensive and quick; foam strips around door and window frames, brushes on letterboxes, and draught excluders at the base of external doors can significantly reduce the volume of cold air entering. Suspended timber floors are a common source of significant floor-level draughts in older properties.

Boiler and Heating System Issues

A boiler that is not operating efficiently or is undersized for the property may not be generating enough heat to maintain comfortable temperatures in cold weather. Signs include the boiler running continuously without reaching the set temperature, radiators that are warm at the top but cold at the bottom (which indicates sludge buildup requiring power flushing), and radiators that are cold overall despite the boiler running (which may indicate air in the system requiring bleeding). A boiler service identifies performance issues that reduce heating effectiveness.

Single Glazing

Single-glazed windows are cold to the touch and cause radiant heat loss from occupants near them, as well as allowing cold air infiltration through gaps in aged window frames. Replacing single glazing with double or triple glazing improves both thermal performance and acoustic insulation, and dramatically improves comfort near windows in winter.

Summary

A cold house is most commonly caused by poor insulation in the loft, walls, or floor, draughts through gaps around doors and windows, a boiler or heating system operating below its best efficiency, or single-glazed windows. Loft insulation and draught-proofing are the most cost-effective first steps. A boiler service addresses system performance issues. Checking thermostat position and settings can resolve comfort issues without any building work.