Is It Cheaper to Leave the Heating On Low All Day?

Ask around in autumn and someone will always say the trick is to leave the heating on low all day so the boiler does not have to work hard to warm the house up. It sounds logical, but for most gas-heated homes it is the wrong way round. Here is why, where the exceptions lie and what actually brings the bills down.

Is it cheaper to leave the heating on low all day?

For most homes with a gas boiler, no. Your house loses heat to the outside all the time, and it loses it faster the warmer it is inside compared with outside. Keeping the house warm while it is empty means paying to replace heat that is escaping for no benefit. Heating it only when needed usually uses less gas overall.

The Energy Saving Trust gives the same advice: set the heating to come on when you need it rather than leaving it on low all the time. The extra effort of warming a cold house back up is smaller than the heat lost by keeping it warm for hours when nobody is there to feel it.

Why does the myth persist?

Because warming a cold house does feel slow and hard work. When the heating first fires, the boiler runs at full output and the radiators take a while to get the rooms comfortable. That makes it seem as if the boiler is wasting energy catching up. In reality, it is simply replacing heat the house lost while it was off, and a cooler house loses heat more slowly.

There is also a grain of truth in it for some homes and some heating systems, which is why the advice gets passed on without the caveats. Those exceptions are worth knowing.

When does leaving the heating on low make sense?

It can make sense with a heat pump, in a very well insulated home, or where damp and condensation are a real problem. It also makes sense if someone is at home all day, because then you are using the heating, not leaving it on for an empty house.

• Heat pumps. They are designed to run for long periods at low temperatures and are least efficient when forced to warm a cold house quickly.
• Very well insulated homes. If a house barely cools down while the heating is off, the saving from switching off is small, and a steady low setting can be as good.
• Damp-prone homes. Solid-walled older terraces, common across the Potteries, can suffer condensation and mould if they get very cold. A modest background temperature may be worth the extra gas.
• Someone home all day. Keeping the home comfortable for the people in it is what the heating is for.

What saves more money than leaving it on low?

Good use of controls. A timer that brings the heating on shortly before you get up and come home, a room thermostat set to a comfortable but not excessive temperature, and thermostatic radiator valves turned down in rooms you do not use will save more than leaving the heating on low for most households.

Smart and programmable thermostats make this easier, especially if your routine varies. Our post on how smart thermostats can save you money covers the options.

Does flow temperature change the answer?

It does, and it is the part most people overlook. A condensing boiler runs most efficiently when the water coming back to it is cool enough to condense, generally below about 55 degrees C. Many boilers are left at a high factory flow temperature that stops them condensing much at all.

Running at a lower flow temperature means the radiators feel less hot to the touch and the house takes a little longer to warm, but the boiler burns less gas for the heat it delivers. That is where the idea of longer, gentler heating does have some merit. Our guides to boiler flow temperature settings and weather compensation explain how to get the balance right without heating an empty house.

What about frost and a cold snap?

Switching off during the day is fine for most homes, but switching off completely in a hard frost is not. When temperatures drop well below freezing, especially if you are away, set the heating to a low temperature or use the frost setting on your thermostat. That protects pipes in cold corners of the house and keeps the boiler's condensate pipe from freezing as easily.

Whatever pattern you choose, it only saves money if the boiler is running properly. A boiler with a dirty heat exchanger or poorly set combustion burns more gas for the same heat, which is one of the practical reasons to book an annual boiler service before winter.

Getting your heating set up for winter in Staffordshire

If you are not sure how your controls are set, or your radiators struggle to heat the house at a lower flow temperature, we can look at the whole system. Our central heating work covers controls, radiators and balancing, and a boiler service is a good moment to ask for advice on settings.

We cover towns across east Staffordshire and Derbyshire too, including boiler service in Uttoxeter and boiler service in Ashbourne. Call 07896 677083 to talk it through.