How much does it cost to run an air purifier?

Most home air purifiers cost about ฿150–1,000 a year in electricity when run 10 hours a day, but replacement filters often cost several times more than that. The cheapest purifier to buy is not always the cheapest to own. Over three years, filters can easily cost more than the purifier itself.

Here is how to work out the real cost before you buy, using the same approach as the running cost section in every AirLab review.

How much electricity does an air purifier use?

An air purifier’s electricity use depends on the watts it draws at the fan speed you actually use and how many hours a day it runs. The number on the box is usually the maximum power on the highest setting. Most people run a purifier on a slower speed, which often uses a fraction of that.

The formula is:

Annual electricity cost (฿) = watts × hours per day × 365 ÷ 1,000 × price per kWh

We use ฿4.5 per kWh as a default. Your actual rate depends on your tariff and usage tier, so check your electricity bill if you want an exact figure.

Power at your speed	10 hours a day	24 hours a day
10 W	฿164 / year	฿394 / year
20 W	฿329 / year	฿788 / year
40 W	฿657 / year	฿1,577 / year
60 W	฿986 / year	฿2,365 / year
100 W	฿1,643 / year	฿3,942 / year

For comparison, a typical room air conditioner draws around 800–1,500 W. Even a large purifier on a middle speed uses far less power than the air conditioner running in the same room.

Don’t forget standby power

Purifiers with Wi-Fi, displays or air quality sensors draw a little power even when “off”. It is usually only 1–2 W. That adds up to less than ฿80 a year if the purifier stays plugged in around the clock. It is small, but worth knowing if you are comparing two very efficient models.

How much do replacement filters cost?

Filters are usually the biggest running cost. How often you replace them depends on the filter’s rated life in hours and how much you use the purifier.

Filters per year = hours used per year ÷ rated filter life (hours)

Annual filter cost (฿) = filters per year × price per filter

Running 10 hours a day adds up to 3,650 hours a year. A filter rated for 2,000 hours needs replacing almost twice a year at that pace. Run the purifier 24 hours a day during haze season and you will go through filters even faster.

A few things to keep in mind:

• Rated filter life assumes average air. During heavy smoke or PM2.5 episodes, filters clog faster than the rating suggests.
• Many filter-change indicators are simple timers. They count hours of use rather than measuring how dirty the filter is. Check the filter visually too.
• Stretching filter life has a cost. A clogged filter restricts airflow. That lowers CADR, so the purifier cleans more slowly and may need a higher, louder speed to keep up.
• Carbon layers can run out before the HEPA layer does. If odors come back, the carbon may be saturated even when particle filtering still works.

Worked example: the cheaper purifier costs more

Here are two hypothetical purifiers for the same bedroom, each run for 10 hours a day at ฿4.5 per kWh.

Purifier A costs ฿6,000. It draws 30 W on the speed you use. Its filter costs ฿1,500 and is rated for 2,500 hours.

• Electricity: 30 W × 3,650 h = 110 kWh, or about ฿493 a year
• Filters: 3,650 ÷ 2,500 = 1.46 filters, or about ฿2,190 a year
• Running cost: about ฿2,683 a year

Purifier B costs ฿3,500. It draws 25 W on the speed you use. Its filter costs ฿1,200 and is rated for 1,200 hours.

• Electricity: 25 W × 3,650 h = 91 kWh, or about ฿411 a year
• Filters: 3,650 ÷ 1,200 = about 3 filters, or about ฿3,650 a year
• Running cost: about ฿4,061 a year

	Purifier A	Purifier B
Purchase price	฿6,000	฿3,500
Running cost per year	฿2,683	฿4,061
Three-year total	฿14,049	฿15,683

Purifier B is ฿2,500 cheaper to buy but about ฿1,600 more expensive over three years, almost entirely because of short filter life. The electricity difference barely matters.

How to keep running costs down

• Size the purifier properly. A purifier with enough CADR for your room can run on a quiet, low-power setting. An undersized one runs flat out, using more electricity and wearing out filters faster. Our CADR guide explains how to size one.
• Compare CADR per watt. Two purifiers with the same CADR can differ a lot in power draw. More clean air per watt means lower electricity bills.
• Use auto mode if the sensor is decent. The purifier speeds up when air quality drops and slows down when it is clean.
• Clean the pre-filter. Vacuuming or rinsing it every few weeks keeps dust off the main filter.
• Keep doors and windows closed. Outdoor air brings in new particles, and the purifier has to keep filtering them.
• Check filter availability before you buy. A cheap purifier whose filters are hard to find or overpriced is not cheap.
• Be careful with third-party filters. They can save money, but a loose fit lets air bypass the filter. Our filter guide explains why the seal matters.

How AirLab measures running cost

We don’t rely on the maximum wattage printed on the box. For every review, we plug the purifier into an energy meter at the wall and record watts at each fan speed. We then calculate annual electricity cost at ฿4.5 per kWh for a realistic daily run time. We add the price and rated life of genuine replacement filters to show the full yearly cost of ownership. The full process is on our methodology page.

The bottom line

Electricity is rarely the expensive part of owning an air purifier. Replacement filters usually are. Before you buy, check the filter price and rated life, multiply by how many hours you will actually run it, and compare the three-year total rather than the sticker price.

Every AirLab review includes a running cost breakdown at real measured wattage. Browse the reviews to compare what each purifier costs to own.