Home Heat Pump Guide

Heat Pump and Draughty House: What to Fix First

If your home feels draughty — cold air sneaking in around doors and windows, floors that chill your feet, rooms that never quite feel warm enough — you might wonder whether a heat pump can cope. The honest answer is that a heat pump will work in a draughty house, but it will work much harder and cost more to run than it should. The good news? Draught-proofing is one of the cheapest and most effective home improvements you can make, and tackling it before your heat pump goes in will pay dividends for years.

This guide explains exactly how draughts affect heat pump performance, identifies the biggest culprits in a typical UK home, and walks you through what to fix first — in a sensible order that maximises impact for minimum cost.

How Draughts Undermine Heat Pump Performance

Heat pumps deliver heat gently and steadily, typically running for longer periods at lower output compared to the sharp bursts of heat from a gas boiler. This approach is highly efficient — but it depends on your home being reasonably airtight. When cold air pours in through gaps and cracks, several problems arise:

Increased heat demand

Uncontrolled draughts increase your home's ventilation heat loss — the energy required to warm incoming cold air to room temperature. In a draughty older home, ventilation heat loss can account for 30 to 40 per cent of total heat demand. That is a significant portion of what your heat pump has to deliver.

Higher flow temperatures needed

When cold air constantly enters, rooms cool down quickly. To compensate, the heat pump may need to run at higher flow temperatures, which reduces its efficiency. A heat pump running at 45 degrees delivers a COP of around 3.5. Push it to 55 degrees to fight draughts, and the COP drops to around 2.8 — a 20 per cent increase in electricity consumption for the same heat output.

Comfort issues

Draughts create cold spots that make rooms feel uncomfortable even when the air temperature is adequate. You end up turning the thermostat higher to compensate, which increases running costs further. A draught-free home at 20 degrees feels warmer than a draughty home at 22 degrees.

What the numbers look like

For a typical three-bedroom semi-detached home, reducing air infiltration from a draughty 15 air changes per hour at 50 Pascals (ach@50Pa) to a reasonable 7 ach@50Pa can reduce total heat demand by 1.5 to 2.5 kW. At current electricity prices, that translates to £150 to £300 per year in lower heat pump running costs — every year, for the life of the system.

The Biggest Draught Culprits (and How to Fix Them)

Not all draughts are created equal. Some gaps let in far more cold air than others. Here is where to focus your efforts, starting with the most impactful:

1. External doors

Front and back doors are typically the single biggest source of draughts in a UK home. Gaps around the frame, under the door, around the letterbox, and through the keyhole all add up.

Solutions:

  • Draught strips around the frame: Self-adhesive foam or rubber strips (£5-£10 per door). Fit them around the door frame where the door meets it when closed. Replace every two to three years as they compress.
  • Brush strip under the door: Screw-on brush strips (£8-£15) or stick-on options for flat-bottomed doors. These allow the door to open and close while blocking draughts underneath.
  • Letterbox draught excluder: A brush-type cover on the inside of the letterbox (£5-£12). Simple to fit and makes a noticeable difference.
  • Keyhole cover: A metal disc that covers the keyhole when not in use (£3-£5).
  • Door threshold seal: For significant gaps under the door, a threshold strip creates a tight seal (£10-£25).

Total cost per door: £25 to £50. Time: 30 minutes to an hour.

2. Windows

Older windows — particularly timber casement and sash windows — develop gaps over time as the wood moves and seals deteriorate. Even modern uPVC windows can lose their seal quality after 15 to 20 years.

Solutions:

  • Self-adhesive draught strips: Foam or rubber strips (£3-£8 per window) fitted to the frame where the opening section meets the fixed frame.
  • Brush strips for sash windows: Specially designed strips that fit into the channel where the sash slides (£15-£30 per window for professional fitting).
  • Window sealant: For gaps between the window frame and the wall, use exterior-grade sealant (£5-£10 per tube, one tube does several windows).
  • Replace perished rubber seals: On uPVC windows, worn rubber gaskets can be replaced without changing the window (£5-£15 per seal).

Total cost for 10 windows: £50 to £150 DIY, or £200 to £400 professionally. Read more about glazing and heat pump efficiency.

3. Suspended timber floors

If your home has original timber floorboards, the gaps between them can be a major source of cold draughts rising from the ventilated void below. This is particularly noticeable on the ground floor of pre-1960s homes.

Solutions:

  • Flexible filler between boards: Specialist flexible fillers (not rigid wood filler, which will crack) pushed into gaps between boards (£20-£50 per room).
  • Sealant at skirting board junction: Decorator's caulk along the gap between skirting boards and the floor (£5-£10 per room).
  • Seal around pipes: Where pipes come through the floor, use expanding foam or sealant to close the gap (£5-£10 total).

Total cost for ground floor: £50 to £150. For more on floor heat loss, see our guide to floor insulation and heat pump performance.

4. Loft hatch

A poorly fitting loft hatch lets warm air escape into the cold loft space — the reverse of a draught, but with the same effect on heat loss. Since hot air rises, an unsealed loft hatch can be surprisingly costly.

Solutions:

  • Draught strip around the hatch frame: Self-adhesive strip around the rebate where the hatch sits (£5-£10).
  • Insulate the hatch itself: Glue a piece of rigid insulation board to the top of the hatch (£5-£10).
  • Add latches: Simple twist catches hold the hatch firmly against the draught strip (£5-£10).

Total cost: £15 to £30. Time: 20 minutes.

5. Chimneys and fireplaces

An open chimney is essentially a hole in your roof. Even when a fire is not burning, warm air rises up the chimney and cold air is drawn into the house through other gaps to replace it. A single open fireplace can account for as much heat loss as leaving a window open.

Solutions:

  • Chimney balloon: An inflatable device that sits in the chimney flue, blocking airflow (£20-£35). Must be removed before lighting a fire.
  • Chimney sheep: A wool-stuffed pad that sits in the chimney (£25-£45). Allows some ventilation while blocking most draughts.
  • Chimney cap: If the fireplace is permanently disused, a cap on the chimney pot with a small vent prevents most heat loss (£30-£80 including fitting).
  • Register plate: A metal plate sealed across the chimney opening above the fireplace (£100-£200 fitted). More permanent than a balloon.

6. Pipework and cable penetrations

Every pipe, cable, and vent that passes through an external wall or floor creates a potential draught path. These are easy to overlook but collectively they can let in significant cold air.

Solutions:

  • Expanding foam: For larger gaps around pipes (£5 per can).
  • Silicone sealant: For smaller gaps and neat finishes (£3-£5 per tube).
  • Draft-proof covers for extractor fan outlets: Replace basic covers with ones that have a gravity flap (£10-£20 each).

The Complete Draught-Proofing Checklist

Work through this list before your heat pump installation. Tick off each item and you will have addressed the vast majority of uncontrolled air leakage in your home:

  • Front door — frame strips, brush strip, letterbox cover, keyhole cover
  • Back door — frame strips, brush strip, threshold seal
  • All opening windows — draught strips or seal replacement
  • Gaps between window frames and walls — exterior sealant
  • Floorboard gaps — flexible filler
  • Skirting board gaps — decorator's caulk
  • Pipe and cable penetrations — foam or sealant
  • Loft hatch — strip, insulation, latches
  • Chimneys — balloon, sheep, or cap
  • Extractor fan outlets — draft-proof covers
  • Cat flap (if applicable) — ensure it closes fully, or fit a microchip-activated flap

What Not to Block

While sealing draughts is important, some ventilation is essential for health and building safety. Do not block:

  • Air bricks below suspended floors: These ventilate the void beneath timber floors and prevent damp and rot.
  • Trickle vents in windows: The small vents at the top of modern windows provide background ventilation. Keep these open.
  • Extractor fans in kitchens and bathrooms: These remove moisture that could cause damp and mould. Ensure they work properly.
  • Boiler flue and combustion air vents: If you still have a gas boiler, its ventilation must not be obstructed. Once you switch to a heat pump, the boiler flue is removed.

If you make your home significantly more airtight, consider whether you need additional controlled ventilation — a mechanical ventilation with heat recovery (MVHR) system recovers 85 to 95 per cent of the heat from outgoing stale air and uses it to warm incoming fresh air. This is common in very well-sealed homes and works brilliantly with heat pumps.

Cost Summary: The Full DIY Draught-Proofing Job

Here is what a complete DIY draught-proofing job costs for a typical three-bedroom semi:

  • Two external doors: £50 to £100
  • Ten windows: £30 to £80
  • Floorboards and skirting: £50 to £150
  • Loft hatch: £15 to £30
  • One chimney: £20 to £45
  • Pipe and cable gaps: £10 to £20
  • Extractor fan covers: £20 to £40

Total: £195 to £465

For that investment, you can expect to save £150 to £300 per year on heat pump running costs, plus immediate improvement in comfort. The payback period is typically one to three years — making draught-proofing one of the best investments you can make before switching to a heat pump.

Professional Draught-Proofing Services

If DIY is not your thing, professional draught-proofing services are available. Specialists can survey your home, identify all the draught sources, and complete the work in a day. Costs range from £300 to £700 for a typical house. Some specialists use a blower door test (pressurisation test) to measure air leakage before and after, so you can see exactly how much improvement has been achieved.

Your heat pump installer may be able to recommend a draught-proofing specialist, or you can find one through the Draught Proofing Advisory Association (DPAA). Check your home's overall readiness with our heat pump suitability checker, and see our full guide on improving your EPC before installing a heat pump.

Frequently Asked Questions

Can a heat pump heat a draughty house?

Yes, but it will cost more to run. A heat pump sized for a draughty home will be larger (and more expensive to buy), and it will consume more electricity because it has to replace constantly escaping heat. Draught-proofing before installation is strongly recommended.

How much does draught-proofing save on heat pump running costs?

Typically £150 to £300 per year for a draughty three-bedroom semi. The exact saving depends on how draughty your home is and the electricity tariff you are on. With a total investment of £200 to £500, the payback is very fast.

Should I draught-proof before or after installing a heat pump?

Before, ideally. This allows the installer to size the heat pump for your improved home. If you draught-proof afterwards, the heat pump may be slightly oversized, though most modern units can modulate their output to compensate.

Will draught-proofing make my home stuffy?

Not if you maintain adequate ventilation. Keep trickle vents open, ensure extractor fans work, and do not block air bricks. If you make your home very airtight, consider an MVHR system for controlled ventilation with heat recovery.

Is draught-proofing worth it even without a heat pump?

Absolutely. Draught-proofing reduces heating costs with any system — gas boiler, electric heating, or heat pump. It also improves comfort immediately. There is no downside to reducing unwanted draughts in your home.

Can I claim any grants for draught-proofing?

Draught-proofing is sometimes included in ECO4 and local authority energy efficiency schemes, particularly for households on qualifying benefits. The Great British Insulation Scheme may also cover it in some cases. Check with your local energy advice service for what is available in your area.