What is the ideal temperature setting for radiators?

There is no single ideal setting for every home. The right temperature depends on the room, how often you use it, your insulation, the size of your radiators and what heats them: a gas boiler, a heat pump or electricity.

Three different settings get mixed up, and they do different jobs:

Recommended room temperatures

These are comfort ranges, not rules. The Energy Saving Trust's advice is to choose the lowest temperature you are comfortable with. If you or someone in the home is elderly, very young or unwell, keep the rooms you use at 18°C or above (the level the World Health Organization gives as the minimum for a healthy home).

What do the TRV numbers mean?

A thermostatic radiator valve does not set the radiator's surface temperature. It senses the air around it and closes once the room reaches the chosen level, then reopens when the room cools. The numbers are approximate and differ a little between manufacturers:

Setting up TRVs and thermostats properly

• Leave the thermostat room open. In the room with your main wall thermostat, keep the radiator valve fully open (or use a manual valve). Otherwise the TRV and the thermostat fight each other.
• Zone the house. Lower settings in bedrooms, hallways and spare rooms. This is where TRVs save the most money.
• Keep the valve head clear. Long curtains, furniture or radiator covers around the valve make it read warmer than the room really is, so it shuts too early.
• Use a steady schedule. A timed programme matched to your routine usually beats switching the heating on and off by hand.
• Replace old TRVs. A valve that is stuck, slow to react or more than ten years old wastes energy. See should I replace my existing TRVs?

What should the boiler be set to?

People often confuse two different boiler temperatures.

• Radiator flow temperature is the heat of the water sent round your radiators. On a modern condensing boiler, about 55–60°C lets the boiler condense, which recovers heat that would otherwise leave through the flue. That is noticeably more efficient than running at 70–80°C. The saving varies from home to home, but it costs nothing to try.
• Hot water temperature is the water at your taps or in your cylinder. If you have a hot water cylinder, store it at 60°C to control legionella bacteria. A combi boiler heating water on demand is usually set to 50–55°C.

Our previous version of this page suggested setting the boiler to 75°C. That is higher than most modern systems need for heating, and it makes a condensing boiler less efficient. If the house only warms up properly at a higher flow temperature, that is usually a sign the radiators are undersized or the system needs balancing, not that 75°C is the right target.

Towel rails and bathrooms

Towel rails behave differently from a standard panel radiator, so the advice above works a little differently for them.

• Central heating towel rails are usually slim and have less surface area than a panel radiator of the same width, so they are more sensitive to a lower flow temperature. On a 55°C flow they will feel warm rather than hot, which is normal. If the bathroom is warm enough, they are working.
• Bathrooms need heat quickly, for a short time. You want 22–24°C around bath or shower time, not all day. Put the rail on a timer or a separate zone rather than turning the whole house up. See should bathroom towel rails be left on?
• Electric and dual fuel towel rails have their own thermostat or timer. In summer, or between heating seasons, a dual fuel rail can run on its electric element alone, so you can warm a bathroom and dry towels without firing the boiler. A typical 300W element running for four hours uses about 1.2kWh, which is roughly 30p at around 25p per kWh. Check your own tariff for the exact figure. More in is electric heating more expensive?
• Safety in bathrooms. Electric towel rails in bathroom zones must have the right IP rating and be installed by a qualified electrician. The timer or fused spur must sit outside the bathroom.

Heat pumps

A heat pump runs at a much lower flow temperature than a gas boiler, typically 35–55°C. Radiators are tested to EN 442 at two standard conditions: ΔT50 (a mean water temperature of about 70°C in a 20°C room) and ΔT30 (about 50°C). A radiator gives out roughly half as much heat at ΔT30 as at ΔT50, so on a heat pump you need larger radiators or more surface area to heat the same room. When you replace radiators, check the ΔT30 output, not just the headline BTU figure. See what is EN 442? and what does flexible heat pump technology mean?

How to cut bills without making rooms cold

• Balance the radiators. If some are piping hot and others barely warm, the system needs balancing using the lockshield valves. See what is a lockshield valve?
• Bleed trapped air. A cold patch at the top of a radiator means air is blocking the flow. See what is a bleed valve?
• Flush an old system. If the bottom of the radiator is cold, sludge is the likely cause. See does flushing radiators improve efficiency?
• Insulate. Draught-proofing, loft insulation and insulated pipework in unheated spaces keep the heat you have paid for. See is it necessary to insulate radiator pipes?
• Right-size the radiator. An undersized radiator forces the boiler to run hotter. Use our BTU guide and the towel rail size guide.

Should I turn radiators off in rooms I don't use?

Turn them down, but do not turn them fully off in winter. Use the low or frost setting (the snowflake). A completely cold room invites damp and mould, and in a hard freeze it puts pipework at risk. Heat from the rest of the house also tends to move into a cold room, which makes the rest of the home work harder.

Frequently asked questions