Last reviewed: August 20, 2026. This guide reflects federal information available on that date. State, Tribal, utility, building-code, and program rules can differ by location.
Reducing uncontrolled air leakage can improve comfort and efficiency. It can also change indoor pressure, humidity, and pollutant concentrations. The goal is not a leaky house or a sealed box; it is a dry, well-ventilated home with controlled air paths.
Key takeaways
- EPA recommends keeping indoor relative humidity between 30% and 50% when possible, and below 60% to help limit mold.
- Dry wet materials within 24 to 48 hours when possible and fix the water source. Cleaning mold without correcting moisture invites recurrence.
- Test every home for radon. EPA recommends fixing at 4 pCi/L or higher and considering mitigation between 2 and 4 pCi/L.
- Use source control first, then appropriate ventilation and filtration. Particle filters do not remove every gas or solve moisture sources.
1. Control water and humidity at the source
Repair roof and plumbing leaks, manage rainwater and grading, maintain condensate drains, and vent showers and cooking outdoors. Track humidity with a reliable hygrometer in problem areas, but interpret the number with season and surface temperatures in mind. Even moderate room humidity can condense on a sufficiently cold window, pipe, wall, or roof surface.
Humidifiers can create hidden condensation in cold climates; dehumidifiers add heat and use electricity; air conditioners remove moisture only while operating. Address the cause rather than relying on one appliance setting.
2. Use local exhaust where pollutants begin
Run a bathroom fan during bathing and long enough afterward to clear moisture. Use a kitchen hood that exhausts outdoors when cooking, especially with combustion appliances. Confirm ducts are connected, terminate outside, and are not crushed or blocked. Recirculating hoods can capture some particles with a suitable filter but do not replace outdoor exhaust for moisture and combustion pollutants.
3. Plan whole-house ventilation
After substantial air sealing, evaluate whether the home needs mechanical ventilation and how much. Exhaust-only, supply-only, and balanced heat- or energy-recovery systems have different pressure, filtration, moisture, climate, and maintenance effects. Intake placement must avoid garages, exhaust outlets, standing water, and other pollutant sources. Commission actual airflow rather than assuming a fan label equals delivered ventilation.
DOE specifically warns that air sealing and ventilation go together. Tighter construction can affect combustion appliances, so fuel-burning furnaces, water heaters, fireplaces, and stoves need appropriate venting and combustion-safety evaluation.
4. Filter particles without choking airflow
For normal conditions, use a filter compatible with the HVAC manufacturer’s requirements. During wildfire smoke, EPA recommends MERV 13 or higher when the system can accommodate the added resistance; ask the manufacturer or an HVAC technician if unsure. A portable air cleaner should be sized to the room using its smoke clean-air delivery rate. Avoid devices that intentionally produce ozone.
EPA’s 2026 filtration guidance says a smoke CADR of at least two-thirds of the room area in square feet is a useful selection rule. Place the unit where people spend time, keep airflow unobstructed, and replace filters when dirty or odorous. Filtration reduces particles in air that passes through the device; it does not repair a leak, remove settled contamination, or guarantee removal of gases.
5. Test for radon
Radon is invisible and odorless, and geography cannot clear an individual home. EPA says its map should not be used to decide whether a house needs testing: all homes should be tested. Follow the device instructions and use a qualified measurement or mitigation professional when required by your state or transaction.
If the result is 4 pCi/L or higher, EPA recommends mitigation. EPA also recommends considering action between 2 and 4 pCi/L because no known level is risk-free. After mitigation, perform the specified follow-up testing, and retest as recommended after major foundation, ventilation, or enclosure changes.
6. Respond correctly to mold
Visible mold or a musty odor is a moisture investigation, not a reason to buy a routine air-sampling kit. Find and stop the water, dry the area, and determine whether porous materials can be cleaned or must be removed. Large areas, contaminated water, HVAC contamination, hidden cavities, or health concerns justify professional help. Never mix cleaning chemicals.
A practical post-retrofit check
After air sealing, insulation, new windows, or HVAC work, verify bath and kitchen exhaust, whole-house ventilation airflow, combustion safety, condensate drainage, indoor humidity, filter fit, and radon as appropriate. Monitor comfort and odors through both heating and cooling seasons. Efficiency is successful only when the home also remains dry, safe, and breathable.
This article provides general educational information, not tax, legal, engineering, or medical advice. Use licensed professionals where permits, combustion equipment, refrigerants, structural work, electricity, or contaminated water are involved.