Air purifier sizing for a master bedroom

Researched from the AHAM AC-1 test method, EPA and CARB guidance, and published manufacturer specifications

Quick answer

A master bedroom is sized at 4.5 air changes an hour against a 9 foot ceiling on this site, so a 300 square foot one needs about 203 CFM of clean air delivery. The table below runs from 200 to 450 square feet.

Required CADR by floor area, 9 foot ceiling
Floor area	Volume	At 2 ACH	At 4.5 ACH	At 6 ACH
200 sq ft	1,800 cu ft	60 CFM	135 CFM	180 CFM
225 sq ft	2,025 cu ft	68 CFM	152 CFM	203 CFM
250 sq ft	2,250 cu ft	75 CFM	169 CFM	225 CFM
275 sq ft	2,475 cu ft	83 CFM	186 CFM	248 CFM
300 sq ft	2,700 cu ft	90 CFM	203 CFM	270 CFM
350 sq ft	3,150 cu ft	105 CFM	236 CFM	315 CFM
400 sq ft	3,600 cu ft	120 CFM	270 CFM	360 CFM
450 sq ft	4,050 cu ft	135 CFM	304 CFM	405 CFM

Meets 203 CFM, the large room class

WINIX 5520 Air Purifier for Home Large Room Up to 1882 Ft2 in 1 Hr With Air Quality Monitor, True HEPA, High Deodorization Carbon Filter and Auto Mode, Captures Pet Allergies, Smoke, Dust.

This machine can be credited with about 502 CFM, derived from the listing's own figures: 1882 sq ft at 2 air changes an hour, assuming an eight foot ceiling. That clears the 203 CFM this room calls for.

$179.99Check pricePrices change often

Check the noise at the speed that delivers the airflow, not the figure quoted for the lowest setting.

Every size in this room type

200 sq ft 135 CFM needed
225 sq ft 152 CFM needed
250 sq ft 169 CFM needed
275 sq ft 186 CFM needed
300 sq ft 203 CFM needed
350 sq ft 236 CFM needed
400 sq ft 270 CFM needed
450 sq ft 304 CFM needed

What makes a master bedroom different

The usual sources in this room are dust mite debris, pet dander, dust raised by a walk in closet and soft furnishing. That mix is what decides whether the carbon stage matters as much as the particle stage, and it is why the same square footage in two different rooms does not always call for the same machine.

Master bedrooms are frequently open to an ensuite and a walk in closet, and an open door is a second room the machine is quietly being asked to serve. Size for the volume that is actually connected, or close the doors.

Which air change target this room is sized at

This section sizes a master bedroom at 4.5 air changes an hour, the allergy and asthma households case, which suits pollen, pet dander or dust mite debris, where somebody in the house notices the difference. Two changes an hour is the comfort baseline and six is where smoke guidance sits.

The target is guidance rather than a measured threshold, so it is worth knowing what moving it does. Going from two changes an hour to 4.5 multiplies the airflow you need by 2.3, and the noise and the filter cost move with it.

Machines sized for this room

Each of these publishes either a CADR or a coverage claim with the air change rate behind it, so it can be compared against the requirement above.

MOOKA
MOOKA H13 HEPA Air Purifier for Home Pet Large Room Up to 1300ft2, Black
- HEPA claimed
- carbon stage
- has a UV lamp
$46.98 Check price
Prices change often
MOOKA
MOOKA Air Purifiers for Home Room up to 1076ft2, True HEPA Filter, B-D02L
- HEPA claimed
- carbon stage
$49.99 Check price
Prices change often
MOOKA
MOOKA Air Purifiers for Home Room up to 1076ft2, True HEPA Filter, B-D02L
- HEPA claimed
- carbon stage
$49.99 Check price
Prices change often
Afloia
Afloia Air Purifier for Large Rooms Up to 2,000 Sq. Ft. with PM2.5 Display
- carbon stage
- washable pre-filter
- particle sensor
- auto mode
$79.99 Check price
Prices change often
KNKA
KNKA Air Purifiers for Home Bedroom Up to 1,695 Ft2 in 1 Hr, APH4000, White
- carbon stage
- washable pre-filter
- particle sensor
- auto mode
$119.97 Check price
Prices change often
Clorox
Clorox Large Room Turbo Air Purifiers for Home With True HEPA Filter
- HEPA claimed
$159.99 Check price
Prices change often

Common questions

What size purifier does a master bedroom need?

Multiply the floor area by the ceiling height, multiply by the air changes an hour you want, and divide by sixty. At 9 feet and 4.5 changes an hour, a 225 square foot master bedroom needs about 152 CFM and a 450 square foot one needs about 304 CFM.

Should I buy one large unit or two smaller ones?

Two smaller machines usually mix a room better than one large one, because a single unit recirculates its own clean air in the corner it sits in. One larger machine is quieter for the same total airflow and costs less to keep in filters. If the room is long or L shaped, two is the better answer more often than the arithmetic alone suggests.

Does the door being open change the sizing?

It does, and by more than people expect. An open door connects the room to a hallway and often to a stairwell, and the machine is then serving that whole volume rather than the room on the floor plan. Either size for the connected space or close the door during the hours that matter.

Is a higher air change rate always better?

No. Airflow costs noise, power and filter life, and past a point the room is already as clean as the filter can make it. The honest ceiling is the arrival rate of whatever you are removing: on a smoke day more is genuinely better, and on an ordinary day in an ordinary house it is not.

Do these figures assume anything about the filter?

They assume the machine delivers its rated clean air delivery rate, which a clogged filter does not. A filter at the end of its life moves less air at the same fan speed, so the effective air change rate drops quietly over months without the machine sounding any different.