Draught Proofing Your Home Before You Spend on Heating

Draught proofing your home means sealing the unwanted gaps around doors, windows, floorboards, loft hatches and unused chimneys so warm air stays in and cold air stays out. It is usually the cheapest way to make rooms feel warmer, and it should come before spending on a bigger boiler or extra radiators, because a heating system cannot keep up with a house that is losing heat through gaps. The one rule that matters most is to never seal air vents or flues that a gas appliance needs to burn safely.

This guide covers where draughts come from, what to use on each gap, what you must leave open, and how to tell whether draughts or your heating are the real problem.

Why draught proofing comes before heating upgrades

A heating system is sized to replace the heat a home loses. When cold air is constantly pulled in through gaps, the boiler and radiators have to warm that air too, and rooms can feel chilly even when the thermostat says they are at temperature. Draughts also make you feel colder than the air temperature, because moving air carries heat away from your skin.

That is why we often suggest tackling draughts before deciding a boiler is too small. Our guide to whether you need a bigger boiler or better insulation explains how to tell the difference, and in many older Stoke-on-Trent terraces the answer starts with doors, floors and windows.

Where draughts come from: a room-by-room checklist

On a windy January day, walk around with the back of a slightly damp hand or a strip of tissue paper and feel or watch for air movement. Common culprits:

Draught excluder doors: the quickest win

External doors and letterboxes are usually the worst offenders, and the fixes are inexpensive and quick to fit. For internal doors, keeping doors closed between heated and unheated rooms often helps more than fitting seals, because you still want some air movement through the house.

Sealing gaps in floorboards

Older houses with suspended timber floors can be very draughty at floor level. Fill gaps between boards with a flexible filler or slivers of timber, and seal along the skirting. However, the space under the floor must still be ventilated through airbricks on the outside walls, or the timber can rot. Never block airbricks.

What you must not block near gas appliances

This is the part of draught proofing that matters for safety. Some appliances take the air they need for burning gas from the room they are in. Building regulations guidance, set out in Approved Document J, covers the air supply and discharge of combustion products for gas, oil and solid fuel appliances. If that air supply is cut off, the appliance can burn poorly and produce carbon monoxide.

Leave these alone:

• Permanent air vents in walls, doors or windows in rooms with an open-flued gas fire, back boiler, older floor-standing boiler or open-flued water heater. Often these are a fixed grille that cannot be closed, and it is there for a reason.
• Vents in cupboards containing an older open-flued boiler.
• The chimney or flue serving any gas fire or appliance. Never fit a chimney balloon, plastic sheet or insulation into a flue that is in use.
• Flue terminals outside the house. Do not cover, box in or wrap them.

Most modern boilers are room-sealed, taking air directly from outside through the flue, so draught proofing the room does not affect them. Older gas fires and back boilers are different. If you are unsure whether a vent serves an appliance, ask a Gas Safe registered engineer before covering it. Our guide to gas fire servicing and safety explains how open-flued fires work, and as Viessmann’s guidance on blocked flues notes, carbon monoxide has no colour or smell, so every home with gas appliances should have a working CO alarm.

If you smell gas, or your CO alarm sounds, open doors and windows, leave the property and call the National Gas Emergency Service on 0800 111 999.

Chimney draught balloons and unused fireplaces

An open chimney with no appliance attached can pull a lot of warm air out of a room. A chimney draught balloon is an inflatable cushion that sits in the flue just above the fireplace opening to reduce that.

• Use one only in a chimney that is genuinely not in use.
• Remove it before lighting any fire, and make sure everyone in the house knows it is there.
• Never use one in a chimney that serves a gas fire, a back boiler or a stove, even if the appliance is switched off.
• A completely sealed chimney can trap moisture, so permanent capping should keep some ventilation. A builder or chimney specialist can advise.

Draught proofing windows and ventilation balance

Draught proofing is about stopping uncontrolled air leaks, not stopping ventilation. Homes still need fresh air to remove moisture from cooking, washing and breathing. The government’s 2026 HHSRS guide for landlords treats damp and mould and excess cold as hazards in their own right and links inadequate heating to damp, which shows the balance you are aiming for: warm, but ventilated.

• Keep window trickle vents open in bedrooms and living rooms.
• Use kitchen and bathroom extractor fans, and do not seal over them.
• Open windows briefly after showering or drying clothes indoors.
• If condensation increases after draught proofing, add ventilation rather than turning the heating down.

Our article on damp, condensation and the role of heating explains how heating and ventilation work together.

Still cold after draught proofing? Check the heating

If you have sealed the main gaps and some rooms are still cold, the problem may be the heating system rather than heat loss:

• Radiators cold at the top need bleeding; cold at the bottom often means sludge.
• Radiators may be too small for the room. A heat loss check and radiator sizing calculation will tell you.
• The room thermostat may be in a warm spot, switching the boiler off too early.
• The boiler flow temperature may be set too low for your radiators in very cold weather.

For low-cost steps alongside draught proofing, read our guide to cheap ways to keep your house warm.

Get your heating checked once the gaps are sealed

Once your home is draught proofed, a properly set up heating system will warm it more evenly and for less gas. If you are unsure whether a vent serves a gas appliance, or rooms are still cold, our Gas Safe registered engineers can check your appliances, radiators and controls. We cover Stoke-on-Trent, Newcastle-under-Lyme, Leek, Stone and the surrounding area. Find out about our central heating services or contact Gasmaster to book a visit.

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