HEPA Filtration

HEPA stands for high-efficiency particulate air. A true HEPA filter is designed to capture at least 99.97 percent of airborne particles measuring 0.3 microns under its rated test conditions, according to the EPA’s HEPA filter definition.

That includes many types of dust, pollen, pet dander, mold spores, bacteria, and smoke particles.

The 99.97 percent rating describes the filter media under a specific test. It doesn’t mean installing a HEPA unit instantly removes 99.97 percent of every particle in your home. The air still needs to reach the filter. Duct leakage, open windows, filter bypass, room layout, fan runtime, and new pollutants all affect the final result.

A HEPA filter also doesn’t work like a simple screen. Particles are captured through several actions as air moves through the deep layer of filter fibers. Larger particles hit or brush against fibers. Very small particles move unpredictably and eventually contact the media.

The filter captures them without releasing ions or intentionally creating ozone.

Whole-Home HEPA Is Different From A Furnace Filter

A true HEPA filter usually can’t be dropped into a standard one-inch furnace filter slot. HEPA media creates more resistance to airflow than many residential blowers and duct systems are designed to handle.

Forcing the wrong filter into the system may reduce airflow. That can cause poor heating and cooling, frozen evaporator coils, high furnace temperatures, noisy ductwork, longer run times, and equipment damage.

There are several ways to improve whole-home filtration:

• A deeper MERV-rated media filter installed in a sealed cabinet
• A dedicated bypass HEPA system with its own fan
• A fully ducted HEPA unit engineered for the required airflow
• Portable HEPA units used in specific rooms

A MERV 13 or MERV 16 filter isn’t automatically the same as true HEPA. However, a properly installed high-MERV filter that receives a lot of airflow may outperform a poorly installed HEPA unit that treats only a small amount of air.

The label matters, but system design matters more.

How HEPA Filtration May Help

Whole-home HEPA filtration may reduce airborne particles that make it through normal housekeeping and basic HVAC filters. It can be especially useful for homes affected by:

• Wildfire smoke or outdoor PM2.5
• Pollen and seasonal allergens
• Pet dander
• Fine household dust
• Nearby construction
• Wood-burning fireplaces
• High outdoor pollution
• Household members who are sensitive to airborne particles

Filtration may help create a more comfortable indoor environment, but it doesn’t cure allergies, asthma, or other health conditions. Results vary based on the person, pollutant, exposure, and home.

HEPA also doesn’t remove gases such as carbon monoxide, radon, or carbon dioxide. It won’t capture most volatile organic compounds or odors unless the system includes separate gas-phase media, such as activated carbon. Even carbon has a limited capacity and eventually needs replacement.

Source control still comes first. Smoke should be exhausted or stopped. Water damage needs to be repaired. A leaking return duct needs to be sealed. No filter should be expected to clean up an unlimited pollutant source forever.

How We Determine What You Need

We don’t recommend HEPA based only on the size of your house. We look at what is in the air, how the HVAC system is built, and how much clean air the filtration system can realistically deliver.

An evaluation may include:

• Reviewing the homeowner’s main concern
• Inspecting the existing filter type and condition
• Looking for gaps around the filter
• Inspecting the return and supply duct system
• Measuring total external static pressure
• Checking blower capacity and airflow
• Reviewing equipment size and fan settings
• Looking for return-duct leakage
• Measuring indoor particle levels when useful
• Comparing indoor and outdoor PM2.5
• Reviewing how often the HVAC fan operates
• Identifying major indoor particle sources

Sometimes the best first step is fixing the existing filter rack. Air takes the easiest path. If there’s a half-inch gap beside the filter, part of the return air may go around the media instead of through it.

A deeper media cabinet may provide enough improvement without needing true HEPA. In other homes, especially where very fine particle control is the goal, a dedicated HEPA system may be worth considering.

We also look at the amount of air the system treats. A very efficient filter moving a tiny amount of air may provide less whole-home cleaning than a slightly lower-efficiency filter moving much more air.

How Whole-Home HEPA Should Be Installed

A whole-home HEPA unit should be installed so air can’t easily bypass the filter. The cabinet, transitions, duct connections, access panels, and filter seals all need to be tight.

A dedicated system may pull air from the return duct, pass it through a prefilter and HEPA filter, and send the cleaned air back into the HVAC system. Some designs use a separate return grille so the HEPA unit can circulate air independently.

Correct installation includes:

• Selecting a unit with enough airflow for the home
• Providing a sealed filter cabinet
• Installing smooth, properly sized duct connections
• Confirming the direction of airflow
• Providing service access
• Installing a prefilter when required
• Measuring airflow and static pressure
• Confirming the main HVAC blower remains within its limits
• Sealing duct and cabinet leaks
• Setting up controls for useful filtration runtime

Running the HVAC fan longer may increase filtration, but there are tradeoffs. It uses electricity, and some systems may re-evaporate moisture from a wet cooling coil if the fan runs continuously after the compressor shuts off. In humid climates, the fan schedule needs to be considered as part of the humidity-control plan.

After installation, the contractor should verify airflow instead of deciding that “air is coming out of the vents” is close enough.

Filter Replacement And Maintenance

HEPA filters collect particles until they’re replaced. As loading increases, resistance usually increases too. Waiting until the filter looks completely packed can reduce airflow and filtration performance.

Replacement time depends on:

• Filter size
• System runtime
• Particle levels
• Pets
• Smoking
• Construction
• Wildfire events
• Prefilter maintenance
• Manufacturer requirements

Some HEPA filters last a year or longer. Others may load faster. A pressure indicator or service reminder is more useful than blindly changing every filter on the same calendar schedule.

HEPA media shouldn’t be washed or vacuumed unless the manufacturer specifically allows it. Cleaning can damage the fibers or seals.

Is Whole-Home HEPA Right For You?

HEPA is one of the most established ways to remove airborne particles. That doesn’t mean every house needs it, and it doesn’t mean every HVAC system can handle it without modification.

American Air Purification can evaluate your particle concerns, existing filter, blower capacity, ductwork, and equipment. We’ll help determine whether you need a better media filter, a dedicated HEPA system, portable room units, duct repairs, or a combination of solutions.

The goal isn’t to sell you the thickest filter we can find. It’s to move enough air through the right filter without hurting the HVAC system.