How to size a humidifier for your room

Match the maker's rated room size to the room you measured.

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Measure the room first

Measure the length and width of the room and multiply them for the floor area. Note ceiling height and whether doors stay open to other rooms.

Read the maker's rating

Look for the maker's rated room size or coverage area on the product page or box. We do not publish a chart. Compare your measured room to that rating for the exact model on the listing.

Tank size and refills

A larger tank means fewer refills. The EPA says to empty the tank, wipe it dry, and refill it daily for portable units, so count the daily routine as part of the size choice.

Too much is a problem too

The EPA says: "Do not humidify to indoor relative humidity levels exceeding 50 percent." Whatever the rating, check the room with a hygrometer so it stays at or below that level.

Whole house units

The EPA says central humidifiers "are built into heating and air conditioning systems, and humidify the whole house." This guide covers portable units.

This is general information, not medical or purchasing advice.

Sources: EPA, Use and Care of Home Humidifiers.

FAQ

How many square feet does a humidifier cover?

It depends on the model. Read the maker's rated coverage for the exact model number.

Can I use one humidifier for two rooms?

Check whether the maker's rating covers the combined space, then check the humidity in both rooms with a hygrometer.

Indoor humidity levels, from the EPA

The EPA ranges, and a hygrometer.

Cool mist, warm mist, ultrasonic, and evaporative humidifiers

Four types, in EPA terms.

Humidifier buying checklist

A short list before you pay.

Next: humidity levels