An air purifier is one of those gadgets people leave switched on around the clock, which makes its running cost a fair question even though the machine itself looks harmless. The good news is that most home air purifiers are low-wattage devices, closer to a couple of LED bulbs than a kettle, so the electricity bill is usually modest. The figure that matters is not the headline wattage printed on the box but the speed you actually run it at, because the gap between sleep mode and turbo can be tenfold or more. Below is what a typical UK household pays, broken down by fan speed and by how many hours a day the unit is on, plus the cost most owners forget to count: the filters.
The short answer. A typical home HEPA air purifier draws 5 to 15 watts on low and 50 to 100 watts on high. Run on a low or auto setting for a normal day, most cost between £10 and £35 a year in electricity. Run flat out 24/7, a powerful unit can pass £130 a year. At 26.11p per kWh (Ofgem cap, July to September 2026), every 10 watts left on around the clock costs about £23 a year.
What an air purifier actually draws
Air purifiers are fan-and-filter devices. The fan pulls room air through a HEPA filter, usually with a carbon layer for smells, and the power it uses depends almost entirely on how fast that fan is spinning. There is no heating element and no compressor, so the wattages are small compared with almost anything in the kitchen or anything that heats or cools.
For a typical home unit sized for a bedroom or living room, you can expect roughly:
- Sleep or low: 5 to 15 watts. About the same as a couple of LED bulbs.
- Medium: 20 to 50 watts.
- High: 50 to 100 watts.
- Turbo or max: 100 watts or more on larger machines.
Units built for large open-plan rooms can peak higher, and the resistance of a dense HEPA filter makes the fan work harder than a plain desk fan of the same size would. Standby draw, for the sensor and the little display, is typically 1 to 2 watts, small enough that it barely registers on a bill.
Many purifiers have an auto mode that uses a particle sensor to sit on low most of the time and only ramp up when it detects dust, cooking smoke or pollen. Auto is usually the cheapest way to run one, because the machine spends most of its life near the bottom of its wattage range and only earns its higher speeds when there is genuinely something to clean. If you want to know your own model exactly, a cheap plug-in energy monitor will read the real draw at each speed in a few seconds, and the result is often lower than the rating plate suggests.
The running cost, speed by speed
The maths is the same as for any appliance. Multiply the wattage by the hours used, divide by 1,000 to get kilowatt-hours, then multiply by your unit rate. The table below uses the current price cap rate and assumes the purifier runs 24 hours a day, which is the worst case but also exactly how many people use them.
| Setting | Power | Per day (24h) | Per year (24/7) |
|---|---|---|---|
| Sleep / low | 10 W | 6.3p | £23 |
| Medium | 30 W | 19p | £69 |
| High | 60 W | 38p | £137 |
| Turbo (large unit) | 100 W | 63p | £229 |
| Auto (mostly low) | ~15 W average | 9p | £34 |
| Low, 8 hours a night only | 10 W | 2.1p | £8 |
At 26.11p per kWh, Ofgem cap July to September 2026. Daily figures rounded.
The pattern is clear. On a sensible low or auto setting, or running only overnight in the bedroom, the cost stays in single or low double figures per year. The bill only climbs once you park the machine on high or turbo around the clock, which most rooms simply do not need once the initial clean-up is done. A purifier on low costs less per year than the standby drain of a typical houseful of set-top boxes and chargers, and the same multiply-and-divide method works for every appliance in the house, so once you have your unit rate to hand you can check anything.
Filters usually cost more than the electricity
For most owners the running cost that actually bites is not the power, it is the consumables. A genuine HEPA filter typically needs replacing every 6 to 12 months depending on how dirty your air is and how hard you run the machine. Carbon filters for odours saturate faster still. A replacement filter or filter set commonly costs £20 to £60 depending on the brand and size, which comfortably exceeds a year of low-speed electricity.
That changes how you should think about the purchase. Two machines with identical wattage can have very different lifetime costs if one takes a £20 generic filter and the other only accepts a £55 branded cartridge. Before buying, look up the filter price and the manufacturer's stated replacement interval, and treat that as the real annual cost of ownership.
A few habits stretch the filter budget:
- Vacuum or rinse the washable pre-filter monthly. It catches the coarse dust and hair, so the expensive HEPA layer behind it loads far more slowly.
- Run auto mode rather than constant high. Less air pushed through the filter means a longer filter life as well as a smaller bill.
- Check whether compatible third-party filters exist for your model. They are often half the price of the branded part.
- Do not run the unit with windows wide open. You are filtering air you are about to throw away, and loading the filter for nothing.
Add filters and power together and the all-in annual cost of a normally used purifier lands somewhere between £30 and £90, with the filter the larger share for anyone running on low or auto.
Room size and CADR: why a bigger unit can run cheaper
Purifiers are rated by clean air delivery rate, or CADR, which is how many cubic metres of cleaned air they push out per hour. The usual guidance is to pick a unit whose CADR can turn over the room's air volume two to three times an hour for general dust and pollen, and more for smoke. A small bedroom of around 30 cubic metres needs far less machine than an open-plan living space.
Here is the counter-intuitive part: a unit that is generously sized for the room is usually cheaper to run than a small one working flat out. Fan power rises steeply with speed, so a large purifier idling on its first or second setting often cleans more air per watt than a compact unit screaming on turbo, and it does it more quietly too. If you are choosing between two sizes for the same room, the bigger one running low tends to win on both noise and pence per day.
Note that air purifiers do not carry the familiar A-to-G energy label in the UK, so you cannot compare them at a glance the way you can a fridge. The habit of reading the technical sheet for wattage and airflow, the same skill our guide to energy labels covers for labelled appliances, is the only reliable way to compare efficiency between models. Watts per unit of CADR is the figure that separates an efficient design from a noisy box.
How to cut the bill
None of this needs a new machine. A few changes get the cost down without losing the air-quality benefit:
- Use auto mode. Letting the particle sensor decide keeps the fan low except when there is something to clean, which is where the real saving lives. Constant high is rarely doing more for you than auto would.
- Run it in the room you are in. A purifier cleaning an empty room all day is wasted power. Move it with you, or use the built-in timer or a plug-in timer for the hours that matter, such as the bedroom from an hour before bed until morning.
- Close the windows while it runs. Trying to filter air you are actively exchanging with outside wastes both electricity and filter life. Air the room first, then close up and let the machine work.
- Tackle the source. Dealing with dust, damp and smoke at the source means the machine works less. If your real problem is condensation and musty air rather than pollen or dust, a dehumidifier may be the better tool for the job, and the two devices solve different problems.
- Match the speed to the moment. Burst it on high for ten minutes after cooking or hoovering, then drop back to low. Short bursts cost pennies; the expensive habit is leaving turbo on out of caution.
And keep perspective on what you are optimising. Even on medium around the clock, a purifier costs less per year than a single degree on the heating thermostat. If the device is helping with asthma, hay fever or a dusty urban flat, the £20 to £35 a year that low or auto mode costs is among the better value lines on the bill.
The bottom line
An air purifier is a cheap appliance to run by UK standards. On a low or auto setting, expect £10 to £35 a year of electricity even with the machine on all the time, and under £10 if you only run it overnight. The cost only becomes noticeable if you leave a powerful unit on high or turbo around the clock, where it can pass £130 and even £200 a year. For most people the replacement filters cost more than the power, so the smart moves are to run auto mode, keep the pre-filter clean, size the unit generously for the room, and check filter prices before you buy. Do that and the air-quality benefit comes at a price most households will barely notice on the bill.