Commercial HEPA Filtration: When MERV 13 Is Enough

Most office buildings do not need true HEPA filtration in the central air handlers. The practical upgrade is a MERV 13 filter, or the highest rating your fans and filter racks can handle, with portable HEPA air cleaners for the few rooms that need more. Commercial HEPA filtration earns its cost in specialized spaces, not in a typical office floor.

The reasoning comes down to what each rating actually captures and what it costs your HVAC system to push air through it. This guide covers the difference between MERV and HEPA, how to decide, and how to upgrade without creating new problems.

What is the difference between MERV and HEPA?

MERV is a rating scale for HVAC filters, and HEPA is a separate, stricter test for a specific class of filter. The Minimum Efficiency Reporting Value scale is defined in ANSI/ASHRAE Standard 52.2 and runs from 1 to 16, with higher numbers meaning higher efficiency. A HEPA filter is one tested to capture at least 99.97% of particles 0.3 micrometers in size (ASHRAE position on infectious aerosols).

That means "MERV 17" and above, which some vendors and older articles use as shorthand for HEPA, are not part of the current MERV scale. EPA's own table notes that HEPA efficiency figures "are not based on the MERV rating system" (EPA, What is a MERV rating?).

Here is how the common ratings compare:

• MERV 8: ASHRAE Standard 62.1 generally requires filters of at least MERV 8, which has no specified minimum efficiency for the smallest particle range (0.3 to 1 micrometer) and 20% in the 1 to 3 micrometer range (ASHRAE).
• MERV 13: minimum efficiencies of 50%, 85% and 90% across the three particle ranges, from the smallest to the largest (ASHRAE).
• HEPA: at least 99.97% for 0.3 micrometer particles (ASHRAE), a size that approximates the most penetrating particle through a filter.

ASHRAE says MERV 8 filters have low effectiveness at reducing exposure to infectious aerosols, and it recommends upgrading to MERV 13 where possible. Its filtration guidance calls for MERV 13 with MERV 14 or better preferred, within what the HVAC system can handle (ASHRAE filtration and disinfection FAQ). That guidance dates from 2020, so check ASHRAE for current updates before putting it in a specification.

Does an office building need HEPA filtration?

Usually not for the whole building. Match the filtration level to the space and its risk.

• General office floors: move from MERV 8 to MERV 13 if the system supports it. EPA's filter guidance is similar: choose "at least a MERV 13 rating, or as high a rating as your system fan and filter slot can accommodate" (EPA).
• Buildings with specific air quality concerns: a site near a busy road or industrial activity, a history of occupant complaints, or tenants in health-sensitive work may justify going above MERV 13 where the equipment allows. A mechanical engineer should confirm what is feasible.
• Critical spaces: ASHRAE notes that in healthcare and other critical applications, higher MERV filters and HEPA filters may be used (ASHRAE). Procedure rooms, laboratory suites and cleanroom-adjacent areas fall here, and their requirements usually come from the tenant's own operations or regulators.

Central HEPA in a conventional office air handler is an engineering project, not a filter swap, because the system has to move air through much more resistance than it was designed for, and that needs a mechanical engineer's review. Targeted portable units are the more practical way to reach HEPA-level cleaning in an executive suite, a wellness room or a sensitive tenant space.

What does a higher-MERV filter do to energy use and airflow?

It raises the resistance the fan works against, and the effect grows with each step up. ASHRAE puts it plainly: increasing filter efficiency generally leads to increased pressure drop, which can reduce airflow through the system, increase fan energy to compensate, or both (ASHRAE FAQ).

The exact penalty depends on the filter model, the face area and the fan. We have not cited a percentage here because published figures vary widely by product, and your own measurements are more reliable. Ask your HVAC contractor to measure pressure drop across the current filters at design airflow and compare it to the air handler's rated capacity.

If the system is already near its limit, a denser filter can cut airflow and make comfort worse. In that case:

• Install the highest rating the system supports without losing airflow.
• Ask your contractor whether deeper filters or a larger filter bank fit, since the same filter rating can resist airflow differently by model.
• Plan fan or motor upgrades as a capital project, and cover critical rooms with portable HEPA units in the meantime.

For a broader walk through the ratings, see our guide to choosing a MERV filter grade.

How do you implement a filtration upgrade correctly?

Choosing the filter is half the job. The rest is making sure all the air actually goes through it.

• Check rack compatibility. Higher-MERV filters are often deeper, so confirm the filter frames fit the tracks in each air handler before ordering.
• Seal bypass paths. Air takes the easy route, so gaps around frames, damaged gaskets and loose access panels can let unfiltered air through. ASHRAE's wildfire smoke guidance calls for mounting filters "with minimal bypass around the filter" (ASHRAE Journal, March 2021).
• Add a way to read pressure drop. The same ASHRAE article recommends adding a port or pressure gauge to at least one air handler, which simplifies deciding when to change filters. Change filters on measured loading, not only the calendar.
• Document the baseline. Record filter type, size, quantity and pressure drop for each air handler so later changes are comparable.
• Keep spares on site. Filters load faster when outdoor air is dirty, and supplies run short in a smoke event.

Facility staff and the HVAC contractor should do this together. A facility management partner can schedule the walk-through, track the results by unit and keep the filter inventory current.

How does filtration hold up in wildfire smoke?

Filtration is the core of a smoke plan, but it works alongside the building envelope and operating mode. Wildfire smoke is mostly fine particulate matter (PM2.5), meaning particles less than 2.5 micrometers across, along with gases.

A planning framework summarized in ASHRAE Journal by authors from EPA, NIST and universities describes a "Smoke Readiness Plan" that includes the following (ASHRAE Journal, March 2021):

• Upgrade recirculation filters to MERV 13 for smoke events, after confirming the HVAC system can run properly with them.
• Put at least a MERV 13 filter on outdoor air intakes, because it captures a large fraction of PM2.5.
• Expect filters to load quickly, since they may need changing as often as daily during heavy smoke, and buy portable air cleaners and extra filters before the season.
• Check dampers and economizers in advance, because an economizer can pull large amounts of smoke into a building.
• Seal cracks around doors and windows and keep them closed.
• Use portable HEPA air cleaners to create cleaner air rooms, and avoid models that produce ozone or ions.

Cal/OSHA's wildfire smoke rule applies when the current PM2.5 Air Quality Index is 151 or greater, and it exempts enclosed buildings where air is filtered by a mechanical ventilation system with windows and doors closed (Title 8 section 5141.1). Your filtration status therefore matters for compliance as well as comfort. We cover the operations side in our wildfire smoke guide for building operations.

One caution on portable units: California requires indoor air cleaners sold or shipped into the state to meet ozone emission and electrical safety standards, with an ozone limit of 0.05 parts per million (California Air Resources Board). Confirm any unit you buy carries CARB certification before it goes into a tenant space.

How should you tell tenants about air quality improvements?

Keep the message short, factual and specific. Say what filter was installed, where, and what that means for smoke days. Avoid promising a level of protection you have not measured.

If you add a low-cost PM2.5 monitor, which the ASHRAE authors suggest, share what it shows in plain terms and note that such monitors are less accurate than regulatory ones but useful for seeing whether your steps are working. Update tenants after major smoke events with what the building did.

Frequently asked questions

Is MERV 13 the same as HEPA? No. MERV is a rating scale that tops out at 16, while HEPA is a separate test requiring at least 99.97% capture of 0.3 micrometer particles (ASHRAE). MERV 13 captures far more fine particles than MERV 8 but does not meet the HEPA definition.

Can I put a MERV 13 filter in any commercial HVAC system? Not always. Higher-efficiency filters resist airflow more, so the system fan and filter housing must be able to handle them. EPA advises using MERV 13 "or as high a rating" as the system can accommodate, and a technician can confirm what yours supports (EPA).

Do portable HEPA air cleaners work for an office? They can clean the air in a single room when sized for the space. ASHRAE recommends a portable cleaner with a HEPA filter, appropriately sized, where the HVAC system cannot sufficiently reduce PM2.5, and notes that larger rooms may need several (ASHRAE Journal). Choose a CARB-certified model.

How often should filters be changed after an upgrade? Base it on measured pressure drop and visible loading, not only a fixed calendar. During heavy smoke, ASHRAE notes that filters may need changing as often as daily. Keep spares on site so you are not waiting on a supplier.

Plan your filtration upgrade with a facility partner

The right filtration plan starts with an honest audit of what each air handler can support. MAFM works as a facilities management partner that plans and coordinates HVAC contractors, schedules filter work and keeps records of each upgrade. Talk to us about facility management to get an air handler walk-through scheduled.