How Much Does an Electric Rooflight Cost to Run?

A fixed rooflight has no running cost because there is nothing in it to feed with power. An electric one adds a motor, a set of sensors and, on a mains-fed unit, a small transformer, and it is worth separating those three when you think about cost, because they behave very differently. The motor itself only draws current while the sash is moving, and a full open-to-close cycle takes seconds, not minutes.

That single fact is why the running cost of an electric rooflight rarely comes up as a real concern at survey. The actuator and controls are built to sip power in short bursts, and everything else about the unit, the glass, the frame, the seals, costs exactly what a fixed rooflight's glass and frame cost to own: nothing, once it is fitted.

A typical chain or spindle actuator on a flat rooflight draws somewhere around 20 to 40 watts while it is running, and a full stroke, open or closed, usually takes 15 to 25 seconds. Multiply those together and one cycle uses a fraction of a watt-hour, closer to a sixth of one than a whole one. Even opened and closed twice a day, every day of the year, that comes to under a fifth of a kilowatt-hour across twelve months.

Set against a typical UK domestic electricity rate, as a guide, that works out at a few pence for the whole year, not per month. It is the kind of figure that gets lost entirely in a household's normal usage, somewhere below a kettle boiled once or a phone left on charge overnight.

Where a rooflight runs from the mains rather than a battery or solar cell, the low-voltage transformer that steps the household supply down sits plugged in around the clock, whether the rooflight is moving or not. Most transformers of this kind draw a small standby load simply by being connected, typically a watt or two.

Left running continuously for a year, even a couple of watts adds up to a handful of kilowatt-hours, which is a bigger share of the total running cost than the motor itself ever contributes. It is still a modest sum on any household bill, roughly what a small phone charger left plugged in costs over the same period, but it is the honest answer to where most of the cost actually sits: in the transformer sitting idle, not the motor doing the work.

Our guide to powering an electric rooflight on mains, solar or battery goes through where that transformer is sited and how the supply is run in from the household circuit.

A solar-powered rooflight charges its own pack from a cell built into the frame, so nothing it does shows up on an electricity bill, whatever the weather. A battery-only unit, recharged by hand from time to time, costs the same negligible amount as charging any small rechargeable pack, and that cost never runs through the household meter either.

Neither option changes how the rooflight opens, closes or responds to a rain sensor. The choice between mains, solar and a battery pack is really about the roof and the room, not about running cost, since all three cost so little to operate that the difference between them is not worth deciding on alone.

A few things push the running cost up slightly, though none of them push it far. A rooflight over a kitchen extension used for purge ventilation several times a day, clearing steam and cooking heat, runs its motor more often than a bathroom vent opened once each morning and evening. A house with several electric units on one circuit, each with its own transformer standing by, carries several small standby loads rather than one.

A rain sensor and a wind sensor also draw a very small current of their own so they can watch continuously for weather, but that draw is smaller again than the transformer's standby load, and it buys the reassurance that a vent closes itself rather than being left open through a downpour on the open Fens around Peterborough. None of this changes the order of magnitude: a handful of electric rooflights on one roof, used daily, still costs a small, single-figure sum across a whole year to run.

What a wall switch, remote or smart home link does to the figure is smaller still, since the switch itself draws almost nothing sitting idle. Setting a schedule so a vent closes at the same time each evening changes convenience, not cost.

The running cost is the smallest number in the whole decision. What genuinely affects what an electric rooflight costs is the unit itself, the size of glass, the actuator, any sensors fitted, and the work to open the roof, fit the frame and make good inside, none of which has anything to do with electricity. Our page on what affects the cost of a rooflight sets those factors out as a general guide.

Keeping the actuator, sensors and any insect screen working well over time is a matter of a simple check now and then rather than an ongoing expense, and our answer on whether electric rooflights need maintenance covers what that involves. Every quote we write also comes with a sightline sketch, so you can see the view and the finished frame before committing to any unit, electric or otherwise, and every install is covered by our 10-year workmanship guarantee, whatever powers the rooflight.

Does opening an electric rooflight more often in summer push the cost up much?

Barely. Even used several times a day through a hot spell, the motor is still only running for seconds at a time, so the extra energy used across a whole summer stays a very small addition to what is already a small yearly figure.

Does a battery-powered rooflight need charging often?

That depends on how often it is used rather than the power source itself. A vent opened daily draws its pack down faster than an access hatch used only occasionally, and how often a pack needs recharging is worth checking against your expected use at survey.

Will fitting several electric rooflights on one roof cost noticeably more to run?

It adds up, but slowly. Each unit still only draws real power for seconds at a time, and each transformer's standby load is small on its own, so a handful of units together still sit at a modest, single-figure yearly sum rather than anything that shows up clearly on a bill.

Does the running cost change if the rooflight is left in a vent position rather than fully closed?

No. Once the sash has reached its set position, whether fully closed, in a trickle vent or holding a purge setting, the motor stops drawing current until it is next told to move. Holding a position costs nothing extra.