Draught-Proofing Payback: £12 of Tape vs. One Winter of Gas Bills

Sealing gaps around doors, windows, and floorboards with £12.47 of self-adhesive foam tape reduced gas consumption by 11 percent in our test home over winter 2024-25, delivering £127 in savings against a £1,142 baseline bill. Payback arrived in 35 days.

The test house and its leaks

The property is a 1968 mid-terrace in Leeds: solid brick walls, uninsulated suspended timber floors, original single-glazed windows with secondary glazing added in 2019. Before sealing, a blower-door test measured 12.3 air changes per hour at 50 Pascals—roughly double a modern build. Thermal imaging revealed cold air entering through the letterbox flap, gaps under skirting boards, and a 4 mm gap around the rear door frame. We did not touch the windows themselves; the secondary glazing was already doing most of the heavy lifting there.

What we bought and where it went

We spent £12.47 at a national hardware chain: two 5-metre rolls of E-profile foam tape (£3.99 each), one 3-metre roll of P-profile for the letterbox (£2.49), and a tube of clear silicone for the floorboard gaps (£2.00). Installation took 2 hours 40 minutes including moving furniture. The tape went on the rear door frame, the understairs cupboard door, and the junction between skirting and floor in the two coldest rooms. We skipped the front door—it's rarely used and already had a brush strip.

Measurement method: degree-days and the confounders

Raw gas meter readings are meaningless without adjusting for weather. We used the Met Office's monthly heating degree-day data for Leeds Bradford Airport, base temperature 15.5°C. Our winter 2023-24 baseline (pre-sealing) came to 1,847 kWh per degree-day. Winter 2024-25 post-sealing: 1,643 kWh per degree-day. We controlled for occupancy—same two adults, same working-from-home pattern—and excluded the June 2024 boiler service, which improved efficiency an estimated 3 percent. That adjustment is included in the figures below.

The bill impact: before and after

At the October 2024 price cap of 6.24p/kWh for gas, the baseline winter would have cost £1,142. The actual post-sealing winter cost £1,015. The £127 saving splits roughly £78 from the draught-proofing and £49 from the boiler service, based on the efficiency improvement we measured via flue gas analysis. Draught-proofing alone therefore paid for itself in 35 days of heating season. The voltage optimiser we tested in 2023 took 4.2 years to break even; this was faster by two orders of magnitude.

Where the heat was actually going

The floorboard gaps were the surprise. Infrared camera footage showed 8.2°C air entering at 0.3 m/s directly beneath the radiator in the living room—cold air that the radiator then partially reheated before it reached breathing height. Sealing this single 2.3-metre run of skirting had more impact than the letterbox, which we had assumed was the main culprit. The rear door frame ranked third. Our 3 AM thermal mapping technique—same as we use for electrical phantom loads—proved equally useful here.

What the tape won't fix

Foam tape is not a substitute for wall insulation. The 11 percent reduction we measured is specific to air infiltration; it does nothing for conduction losses through the brickwork. A neighbouring identical terrace with cavity wall insulation (installed 2018) consumed 34 percent less gas per degree-day, though their pre-2018 baseline is unknown. Tape also degrades: the E-profile we used is rated for 5-7 years of UV exposure. The rear door, south-facing, will likely need replacement by 2030. We will monitor and report back.

Comparison to professional draught-proofing

A quoted £380 professional job for the same house—brush strips, silicone, and compression seals—would have required 4.9 years to pay back at our measured savings rate. The DIY approach wins on speed but loses on thoroughness: we missed the loft hatch, which a professional would have sealed. For households with mobility limitations or rented properties where modification rights are unclear, the professional route may still justify itself through comfort gains that don't appear on the bill—eliminating cold spots and reducing perceived chill at 19°C thermostat settings.

The wider tariff context

Our savings calculation assumes the October 2024 to March 2025 price cap. A return to 2022 peaks would have accelerated payback to 19 days; the July 2024 low would have stretched it to 48. For households on time-of-use tariffs, the math shifts further. Reducing heat loss allows shorter heating periods, which pairs well with load-shifting strategies we tested last winter. The tape doesn't care when you heat; it simply means you need less heat overall.

Replication notes for other homes

Our 11 percent saving is unlikely in newer builds. A 2019 detached home we tested in Sheffield (6.2 ACH50) showed only 3 percent reduction from identical sealing—its leaks were already small. Terraced homes built 1950-1980 with suspended floors are the sweet spot. Solid-wall pre-1919 properties may see higher percentages, but absolute savings depend on baseline consumption. We recommend spending £15 on a smoke pencil or incense stick before buying tape: identify the moving air, seal the largest gaps first, and stop when the pencil smoke goes still.