Is a heated towel rail enough to heat a bathroom?

For a small to medium bathroom (up to ~6m2), a correctly sized towel rail can be the sole heat source. For larger bathrooms, en-suites, or poorly insulated rooms, you may need a supplementary radiator or a larger towel rail. Use our Radiator Sizing Calculator to determine the total heat output needed if adding a radiator alongside a towel rail.

Why do bathrooms need more heat than other rooms?

Bathrooms are designed to a higher temperature standard (22 degrees C vs 21 degrees C for living rooms and 18 degrees C for bedrooms) because occupants are often undressed. They also have higher heat loss from ventilation (extractor fans) and moisture. This means bathrooms need 15-20% more heat per cubic metre than living spaces.

What size towel rail do I need for a small bathroom?

A typical small UK bathroom (2m x 1.5m x 2.4m) needs approximately 600-900 BTU. A standard 800 x 500mm or 1000 x 500mm towel rail usually provides this. For an en-suite shower room, you may get away with a smaller rail as heat loss is lower.

Can I use a towel rail with a combi boiler?

Yes. A central heating towel rail connects to your central heating system just like a radiator. It works with combi, system, or regular boilers. You can also get dual-fuel towel rails with an electric element that works independently of the heating — useful for summer when the boiler is off.

Does hanging towels on the rail reduce heat output?

Yes. Hanging towels or clothes on a heated towel rail can reduce its heat output by up to 50%. The towels act as insulation, preventing heat from radiating into the room. If your towel rail is the sole heat source, consider oversizing by 20-30% to account for this.

Towel Rail Size Calculator — What BTU Heated Towel Rail Do I Need?

How We Calculate This

Our towel rail sizing calculator uses the volumetric heat-loss method adapted for bathrooms. Bathrooms require a higher heat output than other rooms because the target temperature is 22°C (compared to 21°C for living rooms), and they have increased heat loss from ventilation.

The formula

Heat required (Watts) = Room volume (m³) × Adjusted W/m³

We use a base rate of 60 W/m³ for bathrooms (higher than the 50 W/m³ used for standard rooms), adjusted for insulation and glazing quality. An additional 10% is added for the exposed external wall typically found in bathrooms.

Matching to towel rail sizes

We then match the required BTU output to common UK towel rail sizes. Outputs shown are at Delta T 50 (DT50), the current UK standard. When comparing products, ensure the BTU/Watt rating is at DT50 — not the older DT60 standard which shows higher figures.

Important note

If towels will be draped on the rail, the effective heat output to the room is reduced by up to 50%. Consider oversizing or choosing a dual-fuel rail with a supplementary electric element.

Frequently Asked Questions

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Last updated: February 2026

All calculations are estimates. Verify with your supplier.

Towel Rail Sizing Calculator — What BTU Towel Rail Do I Need?