IAQ Priority Order: What to Fix First in a Maryland Home

Priority 1: check for immediate safety problems

Indoor air quality is not only about dust and comfort. Fuel-burning appliances, fireplaces, generators, and furnaces can produce carbon monoxide. The gas can build up indoors and poison people and animals who breathe it.

If a carbon monoxide alarm sounds, or if anyone may be experiencing symptoms that could point to carbon monoxide exposure, leave the area and get everyone to fresh air. Contact emergency services or the appropriate emergency resource from a safe location. Do not stay inside trying to solve the issue by changing an HVAC filter.

CO alarms belong on every level of the home and outside sleeping areas. Test them monthly and replace batteries annually. If the home uses fuel-burning equipment, keep combustion safety separate from ordinary IAQ upgrades. Generators belong outdoors, more than 20 feet from windows, doors, and vents.

• Leave immediately for a CO alarm or suspected poisoning.
• Do not reset equipment or troubleshoot inside an unsafe home.
• Arrange annual service for fuel-burning heating systems, water heaters, fireplaces, and other gas, oil, or coal-burning appliances.

Guidance:CDC carbon monoxide guidanceCPSC CO alarm guidance

Priority 2: stop the source before treating the air

Once an immediate safety issue is ruled out, hunt for the source. Cigarette smoke and renovation dust, a pest problem and a damp crawlspace — each adds something different to the air, and each needs its own fix. A purifier can collect some of what is floating, but it cannot stop whatever keeps producing it.

Source control may mean removing a pollutant, reducing an emission, fixing a leak, changing a product or activity, or isolating a source from the living space. In many cases, it is more cost-efficient than increasing ventilation.

• Walk the home and note where the complaint starts.
• Separate smoke, chemical, renovation, pest, and combustion concerns instead of treating them as the same dust problem.
• Repair a known source before buying an air-cleaning device.

Guidance:EPA source-control guidance

Priority 3: correct moisture and recurring dampness

Moisture can change the house itself, not just the air. Water finds its way in through plumbing, roofs, and foundations; it collects in basements and crawlspaces and around a drain pan that keeps overflowing. EPA recommends keeping indoor relative humidity below 60 percent, ideally between 30 and 50 percent. Wet materials should be dried promptly, ideally within 24 to 48 hours.

If you see mold or recurring dampness, address the water problem instead of assuming more filtration will solve it. CDC does not recommend mold testing as a general response to a mold concern. A visible or recurring moisture problem should lead first to correcting the damp condition and deciding whether specialized help is needed.

• Look for water near the foundation, basement, crawlspace, drain pan, and indoor equipment.
• Use a moisture solution for a moisture problem; a purifier does not remove water from the house.
• Dry wet materials promptly and investigate the condition that keeps them wet.

Guidance:EPA moisture guidanceCDC mold guidance

Priority 4: test for radon instead of guessing

Radon belongs near the top of an IAQ priority list because it is invisible and odorless. A clean-smelling home can still have elevated radon, and a dusty home may not. You need a test to know whether radon is elevated. Maryland's Department of the Environment identifies radon as a naturally occurring gas that can cause lung cancer and directs residents to testing and mitigation resources.

Testing is especially worth considering in a lower level, basement, or ground-floor area. EPA says radon levels are often highest in the lowest part of a building, while any home can have high radon, including homes with or without basements.

EPA recommends fixing a home when radon measures 4 picocuries per liter, or pCi/L, or higher. Homeowners may consider fixing levels between 2 and 4 pCi/L because there is no known safe level of exposure. An HVAC filter or portable air cleaner is not a substitute for radon testing or mitigation.

• Test rather than relying on smell, dust, age of the home, or the presence of a basement.
• Treat an elevated result as a separate mitigation problem, not a filtration problem.
• Use EPA guidance to decide what to do with the result.

Guidance:Maryland radon informationEPA radon action guidance

Priority 5: improve ventilation when outdoor air makes sense

Ventilation can lower indoor pollutant concentrations by bringing in outdoor air and exhausting stale or contaminated air. It is not automatically the next step every day. Outdoor smoke, high pollen, poor air quality, extreme temperatures, and high humidity can make open-window ventilation a poor choice.

Start with the room where the pollutant or moisture is generated. A bathroom fan that exhausts outdoors can remove shower moisture, and a range hood that vents outdoors can remove cooking pollutants and moisture. These targeted actions work at the source rather than moving contaminated air through the rest of the home.

Many residential forced-air heating and air-conditioning systems circulate indoor air without mechanically bringing outdoor air into the home. If spot and natural ventilation do not meet the home's needs, a whole-house ventilation plan may be appropriate.

• Check outdoor smoke, pollen, air quality, temperature, and humidity before opening windows.
• Keep bathroom and kitchen exhaust paths working as intended.
• Ask how incoming outdoor air will be filtered and tempered before adding a whole-house system.

Guidance:EPA ventilation conditionsEPA ventilation guidanceDepartment of Energy home ventilation guide

Priority 6: use filtration for the problem it can address

Filtration makes sense after you have addressed an identifiable source and considered ventilation. It can help reduce some airborne particles, but it cannot correct a leak, a wet basement, a combustion problem, or elevated radon.

A central HVAC filter serves air moving through the system, while a portable air cleaner is designed for a single room or area. The performance of either device depends on how well it collects pollutants and how much air it moves through the filter. Follow the equipment and filter manufacturer's instructions, make sure the filter fits correctly, and do not choose one that creates an airflow problem for the HVAC system.

If the complaint is visible dust, filtration may be one part of the answer. If it is a strong odor, recurring moisture, a combustion concern, or a radon result, look higher in the priority order first.

• Match a central filter or portable unit to the area it can actually serve.
• Confirm the filter fits, is installed in the correct direction, and does not create an airflow problem.
• Treat filtration as a supplement to source control and ventilation.

Guidance:EPA air-cleaner and filter guidanceEPA IAQ improvement guidance

Priority 7: check the HVAC system when symptoms return

The HVAC system may be the source, the pathway, or simply the system distributing a problem that began somewhere else. A dirty filter, blocked return, poor airflow, wet drain area, condensation, or duct issue can change comfort and how particles move through the home. The right response is diagnosis, not an automatic equipment replacement.

Start with observations you can safely make: Is the filter installed in the correct direction? Are supply or return registers blocked? Does one room stay damp or uncomfortable? Is water appearing near the indoor equipment? Do odors return whenever the system runs? These clues help separate an airflow or moisture problem from a source that needs attention elsewhere.

If a fuel-burning appliance is involved, combustion safety takes priority over comfort troubleshooting. If the issue is persistent dust, odor, humidity, or uneven comfort, an HVAC professional can inspect the equipment, ductwork, drainage, filtration, and airflow.

• Write down the symptom, room, timing, and what the HVAC system was doing.
• Check only safe, visible conditions and do not open equipment to investigate.
• Ask for diagnosis tied to the complaint before discussing repair or replacement.