Best for
- People planning continuous purifier use
- Buyers comparing long-term operating cost
- Anyone deciding whether a larger purifier is expensive to run
Watch for
- Using maximum rated wattage as if the purifier always draws that amount
- Ignoring replacement-filter cost
- Comparing operating cost without checking whether both purifiers deliver similar CADR
The 24/7 electricity formula
Annual kWh = watts ÷ 1,000 × 24 × 365. Multiply the result by your electricity price per kWh to estimate annual electricity expense.
A purifier that averages 40 watts continuously uses about 350 kWh per year. Your actual cost depends on the electricity rate you enter and the fan speed the purifier spends most of its time using.
Filter cost can matter just as much
A low-watt purifier can still be expensive if its replacement filter is costly or replaced frequently. Add annual filter expense before declaring one model cheaper to own.
Our ownership-cost calculator combines purchase price, electricity, filter cost and replacement frequency across multiple years.
Compare cost per unit of useful airflow
Operating cost is only meaningful if the machines do the same job. A 20-watt purifier that is too small for the room can be worse value than a 45-watt model that delivers the required CADR.
Size first, then compare ownership cost among models that actually meet the room’s clean-air target.
Use the same basis across brands. Room-size claims, operating-cost assumptions and moisture ratings can use different methods. Normalize the inputs before comparing products.