Hong Life CalculatorsUnderstanding the air purifier running cost calculator — concept and principle
Air purifiers are often left on around the clock, so even a modest wattage adds up over a month. This calculator estimates the electricity an air purifier uses and what it costs per month and per year, from its power draw, daily running hours and your electricity price. It is useful when choosing a fan speed, comparing models or deciding whether continuous running is affordable.
How it is calculated
- kWh per month = W ÷ 1000 × hours per day × days per month
- Monthly cost = kWh per month × price per kWh
- Yearly cost = monthly cost × 12
Enter the power at the fan speed you actually use. Purifiers usually list a range: the lowest setting may draw only a few watts, while the top speed draws many times more. For 24-hour operation, enter 24 hours per day.
The principle
Energy is power × time, and the meter bills in kWh (1,000 W for one hour). In an air purifier almost all the power goes to the fan that pulls air through the filter. Fan power rises steeply with speed, roughly with the cube of fan speed for the same fan and filter, so dropping one speed setting can cut power far more than it cuts airflow. That is why running a purifier continuously on a low setting is often cheaper than short bursts on high, while still keeping particle levels down.
Worked example
- Inputs: 40 W, 24 hours per day, 30 days, $0.25 per kWh.
- Power in kW: 40 ÷ 1,000 = 0.04 kW.
- Monthly energy: 0.04 × 24 × 30 = 28.8 kWh.
- Monthly cost: 28.8 × $0.25 = $7.20.
- Yearly cost: $7.20 × 12 = $86.40.
| Power (W) | Monthly cost |
|---|---|
| 10 | $1.80 |
| 20 | $3.60 |
| 30 | $5.40 |
| 40 | $7.20 |
| 50 | $9.00 |
| 60 | $10.80 |
| 80 | $14.40 |
How to read the result
Compare the electricity cost with what the purifier delivers. The clean air delivery rate (CADR), tested under the AHAM standard in North America, tells you how much filtered air the unit supplies; dividing CADR by watts gives a simple efficiency measure for comparing models. Remember that replacement filters are usually a larger yearly cost than electricity, so add the filter price divided by its replacement interval to get the full running cost.
Common mistakes
- Using the maximum wattage when the unit spends most of its time on low or auto.
- Leaving out filter replacement costs.
- Forgetting standby draw of models with displays and Wi-Fi when they are "off".
Frequently asked questions
Should an air purifier run 24 hours a day?
Continuous running keeps particle levels steady because indoor sources and outdoor infiltration never stop. Low speed keeps the cost small, as this calculator shows.
Does a bigger purifier cost more to run?
Not necessarily. A larger unit can move the same air at a lower, quieter and more efficient speed.
How do I find the real wattage?
Check the specification sheet for power at each speed, or use a plug-in energy meter.
Sources: ANSI/AHAM AC-1, Method for Measuring Performance of Portable Household Electric Room Air Cleaners · U.S. Environmental Protection Agency — Guide to Air Cleaners in the Home