Start with watts, hours and your rate

An air purifier’s electricity cost depends on its power draw, how long it runs and your electricity rate. Room size claims alone cannot tell you the bill.

For example, a purifier drawing 25 watts for 24 hours uses 0.6 kilowatt-hours, or kWh. At $0.20 per kWh, that is $0.12 a day or $3.60 over 30 days. These are example inputs, not a measured result for a model in our guides.

Example costs

These scenarios use 25 and 50 watts at the same electricity price of $0.20 per kWh. They are not model ratings, averages or recommended running schedules. Each pair keeps the hours the same so you can see what changing the power draw does.

Watts Hours per day Electricity per day Cost per day Electricity per week Cost per week Electricity per month Cost per month Electricity per year Cost per year
25 W 8 hours 0.2 kWh $0.04 1.4 kWh $0.28 6 kWh $1.20 73 kWh $14.60
50 W 8 hours 0.4 kWh $0.08 2.8 kWh $0.56 12 kWh $2.40 146 kWh $29.20
25 W 24 hours 0.6 kWh $0.12 4.2 kWh $0.84 18 kWh $3.60 219 kWh $43.80
50 W 24 hours 1.2 kWh $0.24 8.4 kWh $1.68 36 kWh $7.20 438 kWh $87.60

Weeks use 7 days, months 30 days and years 365 days, with the same daily use. Actual power can change with the fan speed and automatic settings.

Estimate your own costs

Enter the watts for the setting you use, the hours per day and the usage-based electricity price from your bill. Twenty cents per kWh is $0.20, not $20.

Your daily use
Per day
$0.12
Per week
$0.84
Per month
$3.60
Per year
$43.80

The starting values are hypothetical: 25 W, 24 hours per day and $0.20 per kWh. They are not a model rating or US average. Uses 7 days per week, 30 per month and 365 per year at the same daily power draw and usage.

The formula is:

Watts ÷ 1,000 × hours × price per kWh = electricity cost

If you already have a measured kWh total, multiply that by your rate instead. Include usage-based delivery charges where applicable. Fixed charges on your bill do not increase just because you run the purifier.

Find a useful wattage

Check the exact model’s label or manual for its power rating. That is a starting estimate, not necessarily the average draw during your day. Do not multiply amps by volts and assume the result is measured watts.

A suitable plug-in energy meter can give you a better estimate for your own settings. Follow its instructions and electrical rating. Measure over a period that includes your normal fan speeds and Auto mode, then use the recorded kWh to estimate the cost.

If you use several fixed speeds, calculate each period separately and add the results. For example, daytime at a higher speed and overnight at a lower speed need not be treated as one constant wattage. Standby power can add a small amount outside the hours you count.

Lower power is not the only goal

A lower fan setting can draw less power while also delivering less clean air. Compare energy use alongside CADR and the room you need to serve. An efficient purifier should provide useful airflow for its electricity use, rather than simply have the lowest wattage on a label.

Keep the intake and outlet clear, and clean the pre-filter and replace the main filter as directed. Do not run with missing or damaged filters to save power. Auto and Sleep modes may change the fan speed, so their names alone do not tell you the cost or the airflow.

Add replacement filters to the budget

Electricity is only part of the running cost. Check the price of the correct replacement filter and the maker’s guidance for changing it. Usage and room conditions can shorten or extend the interval, so a fixed yearly filter bill is only a planning estimate.

Compare the machine price, filter expense and electricity on the same time basis. A modest electricity difference may matter less than a more expensive filter, but use current prices and your own replacement needs before deciding.

Before comparing watts, use our air purifier sizing guide to work out how much clean-air delivery your room needs.

For the other ongoing expense, read when to replace an air purifier filter and check the guidance for your model.