How much does it cost to heat a conservatory?

Where the heat goes

A conservatory loses heat through its roof, its glazed walls, its floor and through draughts round doors and vents. The roof is usually the largest single surface and the one facing the open sky, so it tends to be the biggest single loss. It is also the part you can change most easily.

The examples below focus on the roof, because that is what a replacement changes. We say so clearly so the numbers are not mistaken for the whole room. The walls and floor add to every figure, whichever roof you have.

The sums we use

Heat loss in watts is the U-value times the area times the temperature difference. A 12 m² roof of 16 mm polycarbonate, with a U-value of about 2.3, loses 2.3 x 12 x 20 = 552 W when it is 20°C inside and 0°C outside. The same roof in our 75 mm panels, at about 0.43, loses 103 W.

For a whole year we use heating degree days, which add up how cold it is and for how long. England averages about 2,150 degree days to a base of 15.5°C. Yearly kWh is the U-value times the area times 2,150 times 24, divided by 1,000.

Prices are the Ofgem price cap for 1 October to 31 December 2026: electricity at 26.32p per kWh and gas at 7.97p per kWh. For gas we assume a 90% efficient boiler, so each useful kWh of heat costs 7.97 divided by 0.9, which is about 8.86p. All electric heaters, whether fan, oil filled or panel, turn electricity into heat at the same rate, so the cost per kWh of heat is the same for all of them.

Worked example 1: one cold evening

Say it is 0°C outside and you keep the conservatory at 20°C for four hours after work. This is the heat escaping through the roof alone.

A few pence an hour does not sound like much. The difference is that a heater struggles to keep up with 552 W pouring out of the roof on a cold night, so the room never quite feels warm, while 103 W is easy to replace. That is the comfort side of the numbers.

Worked example 2: a full heating season

This assumes you keep the conservatory warm like any other room from autumn to spring, and it covers the roof only.

Moving from 16 mm polycarbonate to panels saves about 1,158 kWh of heat a year through the roof. That is about £305 a year on electric heating or about £102 on gas. From 25 mm polycarbonate the saving is about £191 on electricity or £64 on gas.

Worked example 3: what people actually spend

Many people heat a conservatory with a 2 kW plug in heater. Running flat out, that costs 2 x 26.32p, or about 53p an hour. Four hours a night for six months, around 180 nights, uses 1,440 kWh and costs about £379.

That figure is close to the roof loss for 16 mm polycarbonate in example 2, which is not a coincidence. In a poorly insulated conservatory, much of what the heater puts out goes straight through the roof. With an insulated roof the same heater reaches temperature sooner and can run on a lower setting or for less time.

A plug in thermostat or a heater with a built in thermostat and timer is the cheapest upgrade you can make. It stops the heater running flat out once the room is warm, whatever roof you have.

Can I run a radiator from the house heating?

Gas is cheaper per unit of heat, but there is a catch. A conservatory is exempt from building regulations only while it has no fixed heating from the house system and stays separated from the house by external quality doors. Adding a radiator off the boiler to an exempt conservatory breaks that exemption.

Once a solid insulated roof goes on, the exemption goes anyway, and the room is treated more like an extension with building control approval. At that point extending the house heating becomes an option, but it should be agreed with building control as part of the work, not added afterwards. Our guide to building regulations for solid conservatory roofs explains the rules.

Does a new roof pay for itself?

Here is the honest version. Our small roofs start from £3,000 fitted. If you heat the room with electricity through the whole season, a saving of about £305 a year means the roof takes about 10 years to pay back on energy alone. On gas, at about £102 a year, it takes much longer, around 29 years.

If you barely heat the room now, there is little energy saving to count, because you are not spending anything. The gain in that case is a room you can use for more of the year, not a lower bill. Most people who replace a conservatory roof do it for comfort first: fewer cold months, a room that no longer reaches 35 to 40°C in summer, less condensation and quieter rain.

Our guide on whether insulated conservatory roof panels are worth it weighs these up in more detail.

Cheaper ways to cut heating costs first

• Close the doors to the house when the conservatory is not in use, so the house heating does not leak into it.
• Use a thermostat and timer on any heater, set to 18 to 20°C rather than flat out.
• Draught proof doors and vents, especially round old sliding doors.
• Add a thick rug on a hard stone or ceramic floor to cut the cold underfoot.
• Consider internal insulation if a new roof is out of budget. It costs about £1,000 to £3,200 fitted, though the old roof stays on top. Our page on conservatory roof insulation compares it with panels.

Next steps

To see what a panel roof would cost for your size and style, use the conservatory roof cost calculator. For the details of the roof itself, read about our insulated conservatory roof panels, then book a free survey for a fixed written quote.