Wildfire Smoke at Your Vacation Rental: What CADR Means for You

In a January 2026 white paper, AHAM, the appliance makers' group that certifies air purifier ratings, warned that many manufacturers size their "room coverage" claims at one air change per hour. In AHAM's model, that cuts a room's particle level by only about 45%, compared with 80% at the room size printed on AHAM's certification seal. For travelers anywhere wildfire smoke can drift, it means the purifier in a rental may be too small for the room even when its box says it isn't. The number to check is the smoke CADR, and EPA's June 2026 wildfire smoke guide gives the sizing rules.

On September 20, 2026, for example, the Bay Area's air district issued a smoke advisory for parts of Sonoma and Marin counties because of the Chileno Fire, warning that conditions can change rapidly.

Key takeaways

CADR (clean air delivery rate) is measured in cubic feet per minute under the ANSI/AHAM AC-1 test. For smoke, use the smoke figure, because the test smoke has the smallest particles of the three it rates.
For everyday use, AHAM and EPA recommend a smoke CADR of at least two-thirds of the room's floor area in square feet. For heavy wildfire smoke, AHAM recommends a smoke CADR equal to the floor area. For a 12-by-12-foot bedroom, that means 96 versus 144. AHAM's math assumes 8-foot ceilings, and EPA says taller ceilings need a bigger purifier.
Air changes per hour (ACH) = CADR × 60 ÷ room volume. A purifier with a smoke CADR of 100 gives about 5.2 ACH in that bedroom but only about 2.4 ACH in a 14-by-20-foot living room with 9-foot ceilings.
Use mechanical filters (HEPA or MERV 13). EPA's 2026 smoke guide does not recommend ionizers or other electronic air cleaners for smoke, and ozone generators can harm your lungs.
Airbnb's Major Disruptive Events Policy covers mandatory orders such as evacuations, unforeseeable natural disasters and large-scale utility outages. It excludes non-binding government guidance. No Airbnb policy page mentions smoke, and our reading is that an air quality advisory alone would not qualify, which leaves your listing's cancellation policy in charge.

What it means for you

Booking a stay in a fire-prone area: ask the host for the purifier's model number and look up its certified smoke CADR in AHAM's directory before you arrive. Prefer listings with air conditioning, and read the cancellation policy. In our reading, a smoke advisory alone does not trigger Airbnb's Major Disruptive Events Policy (see "Refunds, packing and air travel").
Already at a rental when smoke arrives: close the windows, set any air conditioning to recirculate, and turn one bedroom into a cleaner-air room with the purifier running on high. Steps are below.
Traveling with children, older adults, pregnant women or anyone with asthma, COPD or heart disease: EPA counts all of these as sensitive groups, which means taking action from AQI 101 rather than 151. Consider sizing the purifier to the stricter rule (CADR at least equal to the floor area), and see the FAQ on fitting a respirator to a child.
Bringing your own purifier: driving is the simple option; pack a spare filter. TSA's item list has no entry for air purifiers, so read the travel section before you fly with one.

This page is general information, not medical advice. If anyone in your group has heart or lung disease, ask their clinician before smoke season what to do on smoky days, including whether a respirator is safe for them.

What a CADR number actually means

CADR is the volume of clean air a purifier delivers each minute, in cubic feet per minute (cfm). EPA describes it as particle removal efficiency multiplied by airflow, so a purifier with a strong fan and a weak filter, or the reverse, scores lower than one that does both well. AHAM's certification program tests units at independent labs under the American National Standard ANSI/AHAM AC-1 and publishes three CADRs for each: tobacco smoke, dust and pollen. According to AHAM's January 2026 white paper on air changes, these stand for fine, medium and large particles.

Wildfire smoke is mostly fine particles (PM2.5), so the smoke CADR is the one to read. Three details on the label matter:

Fan speed. The certified CADR usually reflects the highest fan speed, according to EPA's 2026 wildfire smoke guide for public health officials. On sleep mode, the purifier delivers less.
Suggested room size. On the AHAM seal, this is the smoke CADR × 1.55. That multiplier gives 4.8 air changes per hour in a room with 8-foot ceilings. AHAM's model, which assumes outdoor air leaks in once an hour, says that keeps the room's particle level about 80% below what it would be with no purifier.
"Covers up to" claims. Claims that are not on the AHAM seal may use a much lower air-change rate. In AHAM's own example, a purifier with a smoke CADR of 100 is suitable for 155 square feet under its method. By the same math, sizing it at one air change per hour, which AHAM says many manufacturers use, would put it at 750 square feet.

Particle filters do not remove gases; EPA notes that odor and gas removal needs activated carbon or a similar sorbent, which is also why a HEPA unit alone won't clear a stale cigarette smell from a listing.

Sizing a purifier for the room

AHAM and EPA give the same everyday rule: choose a purifier with a smoke CADR of at least two-thirds of the room's floor area in square feet. For extremely smoky conditions or people at greater risk, EPA's guide notes that "one recommendation" is a CADR equal to the floor area. AHAM's wildfire guidance recommends exactly that for areas heavily affected by smoke.

EPA lists two more reasons to go above the 2/3 rule: frequent smoke, since filters may last longer in a bigger unit, and noise, since a bigger unit can run at a quieter speed. AHAM's sizing math assumes 8-foot ceilings. EPA says only that a room with a higher ceiling needs a purifier rated for a larger room.

To check any purifier against any room, convert CADR into air changes per hour:

ACH = smoke CADR × 60 ÷ (floor area × ceiling height)
Required smoke CADR = target ACH × floor area × ceiling height ÷ 60

ACH            = how many times per hour the purifier cleans
                 a full room's volume of air
smoke CADR     = certified smoke rating, cubic feet per minute
60             = minutes per hour
floor area     = square feet; ceiling height = feet
target ACH     = 5 for the 2/3 rule, 7.5 for the wildfire rule
                 (at 8-ft ceilings); EPA's guide suggests at least 4 to 5

Illustrative example. A rental has a 12-by-12-foot bedroom with an 8-foot ceiling: 144 square feet and 1,152 cubic feet. The host's purifier has a smoke CADR of 100. In the bedroom, that's 100 × 60 ÷ 1,152 = 5.2 air changes per hour. That passes the 2/3 rule (96) but falls short of the wildfire rule (144, or 7.5 ACH).

Moved to a 14-by-20-foot living room with 9-foot ceilings (2,520 cubic feet), the same purifier delivers 100 × 60 ÷ 2,520 = 2.4 air changes per hour. In AHAM's model, which assumes outdoor air leaks in once an hour, that cuts particles by about 66% rather than about 81% in the bedroom. The lesson is to put the purifier in the room where you sleep and close the door, not in the open-plan living area.

Room (illustrative)	Volume	Smoke CADR, everyday (about 5 ACH)	Smoke CADR, heavy smoke (7.5 ACH)	ACH from a 100-cfm purifier
10 × 12 ft bedroom, 8-ft ceiling (120 sq ft)	960 cu ft	80	120	6.3
12 × 12 ft bedroom, 8-ft ceiling (144 sq ft)	1,152 cu ft	96	144	5.2
14 × 16 ft primary bedroom, 8-ft ceiling (224 sq ft)	1,792 cu ft	149	224	3.3
14 × 20 ft living room, 9-ft ceiling (280 sq ft)	2,520 cu ft	210	315	2.4
20 × 20 ft studio, 8-ft ceiling (400 sq ft)	3,200 cu ft	267	400	1.9

The CADR columns for the 9-foot room are our own calculation: they scale the rules by ceiling height ÷ 8, which keeps the air changes per hour the same as at 8 feet. Modeled reductions are for comparison, not predictions: in real homes during smoke events, EPA's guide reports portable purifiers cut indoor PM2.5 by 50% to 80%, about 65% on average. In large rooms, EPA notes, two smaller units may cost less than one big one.

HEPA, ionizers and DIY box fans

EPA's 2026 guide divides purifiers by how they work. Mechanical filters, including HEPA and other pleated filters, trap smoke particles well and do not produce ozone. EPA's filter table rates HEPA at 99.97% or higher efficiency.

Electronic purifiers, such as ionizers and electrostatic precipitators, have "limited evidence" of removing smoke PM2.5 and are not recommended for smoke. They can also produce ozone or other byproducts.

Ozone generators are worse. EPA's page on ozone generators sold as air cleaners says no federal agency has approved them for use in occupied spaces. It adds that at concentrations below public health standards, ozone is generally ineffective at cleaning indoor air.

EPA's 2026 guide advises using only purifiers certified by the California Air Resources Board. CARB certification is required for sale in California, so a unit bought elsewhere may not have it. To be certified, electronic models must stay within an ozone emission limit of 0.050 parts per million, and you can look a model up on CARB's certified list. CARB states that it does not evaluate how well certified purifiers remove pollutants, so check the CADR as well.

If no commercial purifier is available or affordable, a box fan with a MERV 13 furnace filter attached is a tested fallback; EPA presents it as a temporary alternative, not a permanent one. EPA measured wildfire-smoke CADRs of about 111 for one 1-inch filter, 156 with a cardboard shroud, and 401 for a four-filter cube, according to its research on DIY air cleaners. Its safety conditions:

Use a box fan made in 2012 or later with a UL or ETL safety mark. EPA does not recommend older fans, and if one is used, it should not run unattended or while you sleep.
Don't use a damaged or malfunctioning fan or an extension cord, don't leave children alone with the running fan, and make sure the rental has working smoke detectors.
Check the filter daily during a smoke event, and change it when it turns dark brown or gray or smells of smoke. EPA found that DIY units with dirty filters were almost completely ineffective.

When smoke reaches your rental

Check conditions on the AirNow Fire and Smoke Map, which EPA calls the primary source during smoke events. It shows a NowCast reading that gives the most weight to recent hours when smoke changes quickly. The table condenses EPA's 2026 cautionary statements for each AQI category.

AQI	Category	Sensitive groups	Everyone else
0–50	Good	No precautions	No precautions
51–100	Moderate	Unusually sensitive people: consider shorter, less intense outdoor activity	No precautions
101–150	Unhealthy for Sensitive Groups	Shorter, less intense outdoor activity with more breaks; keep asthma action plans and quick-relief medicine handy	No specific precautions
151–200	Unhealthy	Consider moving all physical activity indoors to cleaner air	Keep outdoor activity shorter and less intense
201–300	Very Unhealthy	Avoid all outdoor physical activity	Limit outdoor physical activity
301+	Hazardous	Stay indoors in cleaner air, keep activity light	Avoid all outdoor physical activity

EPA's sensitive groups are people with heart or lung disease, older adults, children and teenagers, and pregnant women. From the Moderate level up, EPA says to go inside to cleaner air if you have symptoms such as coughing or shortness of breath. From AQI 101 up, people with heart disease should contact a health care provider if they notice palpitations, shortness of breath or unusual fatigue. EPA also advises more caution during prolonged smoke events.

Inside the rental, EPA's clean room steps and its 2026 guide translate into a short list:

Seal and recirculate. Close windows and doors without blocking your exit. Set air conditioning to recirculate, turn off any fresh-air setting, and set the thermostat fan to "On" so more air passes the central filter. Use bathroom and range fans briefly, and single-hose portable ACs and swamp coolers sparingly, since they pull in outdoor air.
Pick one room. A bedroom with an attached bathroom works well. Run the purifier there continuously on the highest speed you can tolerate, with nothing blocking its airflow; AHAM advises moving it toward the center of the room rather than into a corner.
Cut indoor sources. Skip smoking and vaping, gas, propane or wood-burning stoves, candles, incense, frying or broiling, aerosol sprays and vacuuming, unless the vacuum has a HEPA filter.
Message the host. Ask how the fresh-air setting works, whether spare or MERV 13 filters exist, and whether a second purifier is available. Don't alter their system unasked; EPA cautions that not every system can handle a MERV 13 filter.
Watch the heat. EPA warns that staying shut in without air conditioning can be dangerous in hot weather. If the rental can't stay cool, loses power or stays smoky, go elsewhere.
Be ready to leave. EPA's clean room page stresses that conditions can change quickly. In an unfamiliar place, check how you'll get local emergency alerts and learn your evacuation routes on arrival.

If you must be outside, the CDC's wildfire safety guidance says an N95 or P100 respirator is the most protective option; EPA adds that it must be NIOSH-approved. It also has to seal: beards prevent a good seal, a one-strap paper mask gives little or no protection, surgical masks give less than a respirator, and N95s filter particles but not gases.

Respirators carry risks too. EPA says people with heart or lung disease should consult a health care provider before using one. Anyone who has trouble breathing or feels dizzy or faint while wearing one should take it off and move to cleaner air. Wearing one during activity or in heat can raise the risk of heat-related illness.

Refunds, packing and air travel

What Airbnb's policies cover

Airbnb's Major Disruptive Events Policy (checked October 3, 2026) does not mention wildfire smoke. It applies only when an event affects the reservation location, happens after booking, and prevents or legally prohibits completing the stay. Covered events include mandatory government travel restrictions such as evacuation or shelter-in-place orders, unforeseeable natural disasters, and prolonged outages of essential utilities such as electricity that affect the vast majority of homes in a location.

The policy excludes "non-binding travel advisories or other government guidance that fall short of a travel ban or prohibition." It also excludes weather or natural conditions common enough to be foreseeable in a location, unless they trigger a covered event such as a mandatory evacuation.

Airbnb decides whether to activate the policy for a defined area and period. When it does, guests can cancel for a refund, travel credit or other consideration regardless of the cancellation policy. If you think it applies, Airbnb says to contact it about eligibility.

Our reading: an air quality advisory like the Bay Area's is guidance rather than an order, so on the policy's wording it would not qualify by itself. Airbnb has not addressed smoke advisories directly. If the policy doesn't apply, your listing's cancellation policy governs, and any extra refund is up to the host.

Airbnb's list of foreseeable conditions it may exclude currently names winter weather, tropical storms and endemic diseases, but not wildfires. Airbnb says the list is not exhaustive.

One related protection: under Airbnb's rebooking and refund policy for homes, an advertised feature that doesn't work, such as air conditioning, counts as a "Reservation Issue." The policy's examples (pool, hot tub, major appliance, heating, air conditioning) don't mention air purifiers, so whether a broken advertised purifier qualifies is Airbnb's call. You must contact Airbnb or the host within 72 hours of discovering the problem, try to resolve it with the host first where feasible, and provide evidence such as photos. Airbnb then decides on a full or partial refund or help rebooking.

Bringing your own purifier

By car, just pack a spare filter. For flights, TSA's "What Can I Bring?" list had no entry for air purifiers or replacement filters when checked on October 3, 2026. The closest entry, electric fans, is allowed in carry-on and checked bags, subject to your airline's size limits. TSA states that the officer at the checkpoint makes the final decision.

If the unit uses lithium batteries, TSA's battery rules require spares to travel in carry-on bags only, and rechargeable spares are limited to 100 watt-hours each. Batteries installed in a device fall under the FAA's rules for portable electronic devices.

Frequently asked questions

Does the smoke CADR on the label measure wildfire smoke?

No. AHAM measures CADR with tobacco smoke, dust and pollen, not wildfire smoke. EPA measured wildfire-smoke CADRs separately for its DIY designs. The tobacco-smoke number is still the right one to use, because it covers the smallest particles and is the figure both AHAM's and EPA's sizing rules are built on.

How often should a purifier's filter be changed during a smoke event?

More often than the manual suggests. EPA advises replacing filters when they look dirty or start to release smoke odor, and again once the smoke event ends. AHAM adds that a change in filter color or weaker airflow from the purifier are signs a filter is due, and it suggests keeping spares on hand during wildfire season.

Can young children wear an N95 respirator in smoke?

NIOSH does not approve respirators for children. EPA's 2026 guide says most children 2 and older can wear one, though a good fit is hard to find for ages 2 to 7. A child should be able to tell an adult about problems with the mask and take it off without help. If not, EPA advises relying on cleaner-air spaces instead.

Will a humidifier help with smoke indoors?

No. EPA's 2026 guide says humidifiers are not air cleaners and will not meaningfully reduce PM2.5 or remove gases. In a dry climate, moister air may ease eye and airway irritation, but that hasn't been studied in smoke events. A poorly cleaned humidifier can also spread mold spores.

How do I limit smoke in the car when driving out?

Keep the windows closed and run the air conditioning on recirculate. EPA notes that most vehicles can recirculate inside air, which helps keep PM2.5 lower, but a car gives less protection than a cleaner-air room. On long drives or with several passengers, EPA suggests briefly opening a window or the outside-air intake when smoke is lighter, because carbon dioxide from breathing can build up quickly in newer cars. Never leave children or pets in a closed car, don't use the car as a smoke shelter, and consider replacing the cabin filter after a heavy smoke event.

Smoke-day checklist for renters

Before you go, get the model number of the host's purifier and look up its smoke CADR in AHAM's certified directory.
Measure the bedroom you'll sleep in and work out its target smoke CADR: two-thirds of the floor area for everyday use, the full floor area for heavy smoke or a sensitive traveler, scaled up for ceilings above 8 feet.
If the purifier falls short, ask the host for a second one, or bring your own HEPA purifier with a spare filter.
When the Fire and Smoke Map shows AQI above 100, or earlier if anyone is unusually sensitive or you smell smoke indoors, close up the rental, set the air conditioning to recirculate, and run the purifier on high in that one room with the door shut.
Pack NIOSH-approved N95s for adults who need to go outdoors, and check the fit before you need them.
If an evacuation or shelter-in-place order is issued for your rental's location, follow it first, then contact Airbnb about the Major Disruptive Events Policy. If the advertised air conditioning fails, report it within 72 hours of discovering the problem, with photos.