Work out what an air purifier really costs you per year — electricity and filters — and see how a low-wattage MERV-13 unit compares with a typical HEPA tower. Adjust every figure to your own tariff and usage.
Estimates only. Electricity cost = power (kW) × hours/day × 365 × your unit rate. Filter cost is your figure. Actual use varies; a purifier only cleans while it's switched on.
Two things decide what a purifier costs you: the electricity it draws while it runs, and the filters it gets through. Electricity is simple physics — a unit's wattage times how long it runs times your tariff. The catch most "best of" lists skip is that wattage varies enormously: an efficient MERV-13 unit built on the Corsi-Rosenthal principle draws roughly 6–18 watts, while a sealed HEPA tower often pulls 60–120 watts to move the same clean air. Over a year of continuous running that gap is the difference between pounds and tens of pounds.
Filters are the other half. Standard MERV-13 media is cheap and replaceable; proprietary HEPA cartridges typically cost £50–80 a year. Add the two together and the cheaper-to-run unit is usually the one that actually gets left switched on — which is the only way a purifier cleans anything.
At a typical unit rate around 28p/kWh, a 15-watt unit run 24/7 costs roughly £37 a year in electricity; a 90-watt tower run the same way is nearer £220. Use the calculator above with your own tariff and hours for an exact figure.
Yes — power (and cost) drop with fan speed, but so does clean-air delivery. A larger, high-airflow unit run gently usually beats a small one at full tilt: same clean air, less noise, lower cost.
They should. A cheap-to-power unit with expensive proprietary filters can cost more overall than the sticker suggests. The calculator adds both so you compare like for like.
More on choosing a low-cost, low-noise unit: read how to choose on CADR, HEPA vs MERV-13, or see our overall pick.