What an air purifier really costs

The price of an air purifier is only the start: every year you pay for electricity and, above all, for replacement filters. And a purifier only helps if it is powerful enough for the room you put it in. This calculator does both: it estimates the annual cost, split between energy, filters and the unit, and works out how many times an hour the purifier can filter all the air in the room.

It works in any currency: enter real prices and the figures from your model's specification sheet.

How the calculation works

• Air changes per hour: the CADR, the clean air delivered in m³/h, divided by the room volume.
• Energy: power at the speed you use × hours a day × days, times the energy price.
• Filters: filter price × how many times you change it in a year.
• Unit: purifier price divided by its lifespan in years.

The verdict is based on air changes per hour, which tell you whether the purifier suits the room, and adds the annual cost.

How much CADR your room needs

A widely used rule of thumb, from the US Association of Home Appliance Manufacturers (AHAM), asks for a CADR of at least two thirds of the room area in square feet, with CADR in cubic feet per minute: that is about 5 air changes per hour. With 2.5 m ceilings and 5 air changes per hour:

The stated CADR usually refers to the top speed: if you run the purifier at a lower, quieter speed, the real CADR is lower.

Filters weigh more than electricity

With a 30 W purifier on 8 hours a day all year, energy at 0.30 per kWh, a 40 filter and a 150 unit lasting 6 years:

Before buying a purifier, check the price and stated life of its filters: they often determine the long-term cost more than the price of the unit.

How much running hours matter

With the same figures and the filter changed every 6 months:

Even running day and night, an efficient purifier uses little power; the real filter life, however, shortens if the unit works harder or the air is very dusty.

The bands of the verdict

• Under 2 air changes per hour: undersized for the room.
• 2 to 4: borderline; it cleans slowly.
• 4 to 6: adequate, in line with the rule of thumb.
• Over 6: capacity to spare; you can run it at a lower speed.

Limits of the calculator

Air changes assume the purifier filters the whole room evenly; furniture, open doors and the unit's position change the result. CADR should be read from the model's specification sheet and refers to the top speed. The calculator does not assess effectiveness against specific pollutants or allergens: for particular health needs, follow medical advice.

Frequently asked questions

How much does an air purifier cost per year?

Mostly it depends on filters. With 30 W for 8 hours a day, a 40 filter every 6 months and a 150 unit over 6 years, you spend about 131 a year, 80 of it on filters.

How much electricity does an air purifier use?

Little: many models draw 20-50 W at medium speeds. At 30 W for 8 hours a day that is about 88 kWh a year.

What is CADR?

It is the amount of clean air the purifier delivers, in m³/h or cubic feet per minute. The higher it is, the faster it cleans the room's air.

How much CADR does my room need?

A widely used rule of thumb aims for about 5 air changes per hour: a 20 m² (215 ft²) room with a 2.5 m ceiling needs about 250 m³/h (147 cfm).

What are air changes per hour?

How many times an hour the purifier filters a volume of air equal to the room: CADR divided by the volume.

How often should the filter be changed?

It depends on the model and use, often every 6 to 12 months. Running it many hours a day or in dusty spaces shortens filter life.

Is a bigger purifier than needed worth it?

Often yes: it can run at a lower, quieter, more efficient speed while keeping a good number of air changes.

Does the stated CADR apply at every speed?

No, it usually refers to the top speed. At low speeds the real CADR is lower.

Can one purifier clean the whole home?

A unit works well in one room. Several rooms need several units or a very high-CADR model, and closed doors limit the effect.

Does a purifier replace ventilation?

No: it filters particles but does not renew the air or remove humidity or carbon dioxide. Opening windows still matters.

Does the calculator assess effectiveness against allergens?

No, it only estimates air changes and cost. For allergies or asthma, follow medical advice.

Does it work in any currency?

Yes. Enter all prices in the same currency; air changes do not depend on the currency.