For a portable unit, multiply your room's square footage by 2/3 to find the minimum Clean Air Delivery Rate (CADR) you need, this delivers roughly 4.8 air changes per hour, a level commonly recommended for allergy and asthma relief.
For whole-house systems installed in your HVAC return ductwork, sizing is based on your home's total square footage and duct capacity, not individual rooms.
We spend roughly 87% of our time indoors, according to the National Human Activity Pattern Survey (NHAPS), the U.S. EPA-funded study that remains the primary data source on indoor time exposure. Most of that time happens at home, where cooking, cleaning products, pet dander, and off-gassing materials combine with outdoor particles that make their way inside.
Picking an air purifier shouldn't require decoding marketing buzzwords. The real question is simple: what size air purifier do you actually need? The answer depends on two things: whether you need a portable or whole-house system, and the area you want to cover.
The most common point of confusion is the "coverage area" printed on the box and it means something different depending on the device type.
Portable purifiers are built for a single, enclosed room. A unit rated for 500 square feet assumes the air stays within four walls. Our portable unit, Biopur, is rated to clean up to 800 cubic feet: ideal for a bedroom, nursery, or home office.
Systems like the R Max or SR Max (not available in Canada) install directly into your HVAC return ductwork. Instead of treating the air in one room, they treat the full volume of air moving through your central heating and cooling system.
For a whole-house system, the real sizing question isn't room dimensions; it's your home's total square footage and your HVAC return duct capacity. Standard homes are straightforward to size; complex or multi-zone layouts benefit from an expert assessment.
Talk to a Sanuvox sizing specialist here →Contact Us
If you're buying a portable unit, ignore the vague "room size" label on the box and look for the Clean Air Delivery Rate (CADR) instead. Developed by the Association of Home Appliance Manufacturers (AHAM), CADR measures the volume of filtered air a unit delivers, in cubic feet per minute (CFM).
To reach approximately 4.8 air changes per hour (ACH), a level often cited for allergy and asthma control, use this formula:
Room Area (sq. ft.) × 2/3 = Minimum Smoke CADR Required
|
Room Size (sq. ft.) |
Minimum Smoke CADR (for 4.8 ACH) |
Example Use Case |
|
150 |
100 |
Small bedroom or nursery |
|
300 |
200 |
Master bedroom or home office |
|
500 |
335 |
Large living room |
|
675+ |
450* |
Large open-plan main floor |
Ceiling height: These calculations assume standard 8-foot ceilings. For 9-foot ceilings, multiply your required CADR by 1.13. For 10-foot ceilings, multiply by 1.25.)
It’s tempting to buy cheaper filters from other retailers, but are they really worth it in the long run?
First of all, CADR is tested with a new, manufacturer-genuine filter so a purifier's rated coverage only holds up if you keep using genuine replacements.
Also, off-brand filters are often thinner, with less filter media, and may show a decent CADR on paper while degrading far faster in real use. When you skip genuine manufacturer filters, you open the door to these concrete risks:
Reduced airflow: poor construction strains your HVAC or purifier motor.
Lower efficiency: failure to capture the 99.97% of fine particles HEPA filters are rated for.
Contaminant bypass: substandard seals let allergens and viruses leak around the filter instead of through it.
Find your filters here: replacement filters.
A unit marketed as "silent" almost always means it has no fan and if a unit isn't moving air, it isn't cleaning it.
Air purification is a mechanical process: air has to physically pass through a filter or past a UV source. That creates an unavoidable trade-off between noise and performance, since higher fan speeds move more air, which is what drives the air changes per hour (ACH) needed to actually improve your air.
If you need quiet performance for a bedroom, the Biopur is built for that balance.
Our engineering team built a free residential sizing tool that calculates your Clean Air Delivery Rate (CADR) for you. To use it:
Choose your home type
You'll get a recommended system matched to your home's specs.
What size air purifier do I need for a 500 sq ft room?
For a 500-square-foot room, use the 2/3 rule: 500 × 2/3 = a minimum Smoke CADR of about 335. Choose a portable unit rated at or above that CADR to achieve roughly 4.8 air changes per hour.
Is CADR more important than the "room size" listed on the box?
Yes. "Room size" is a marketing estimate; CADR is an AHAM-tested measurement of how much filtered air a unit actually delivers per minute. Two purifiers with the same room-size rating can have very different CADR values and real-world performance.
Do I need a bigger air purifier if I live in a wildfire-smoke area?
Yes. The standard 2/3 rule assumes typical indoor air quality. In wildfire-prone regions, size for a 1:1 ratio, a Smoke CADR equal to your full room square footage for adequate protection during smoke events.
Can one portable air purifier clean my whole house?
Generally no. Portable units are designed to treat a single enclosed room; air doesn't circulate efficiently between rooms and floors. For whole-home coverage, a system installed in your HVAC return ductwork (like the R Max or SR Max) treats all the air moving through your central heating and cooling system.
How does ceiling height affect air purifier sizing?
Standard sizing charts assume 8-foot ceilings. Higher ceilings mean more air volume to clean, so multiply your required CADR by 1.13 for 9-foot ceilings or 1.25 for 10-foot ceilings.
How often should I replace my air purifier filter?
Replace filters every 6 months to 3 years, depending where they are installed, also by using genuine manufacturer filters. CADR ratings are tested with new genuine filters; off-brand filters can degrade performance faster and reduce the unit's effective coverage area.
Ready to find your exact fit? Try our free sizing tool or talk to a Sanuvox specialist about your home's HVAC setup.