What Is HEPA/ULPA Filtration for HVAC

HEPA and ULPA filtration are high-efficiency air cleaning technologies that can be integrated with HVAC systems to capture microscopic particles that standard filters miss. For homes and commercial buildings facing wildfire smoke, allergies, sensitive processes, or strict indoor air quality (IAQ) goals, understanding how HEPA/ULPA fits into HVAC is essential.

HEPA vs. ULPA: How They Are Defined

HEPA (High-Efficiency Particulate Air) filters capture at least 99.97% of particles at 0.3 micron—the most penetrating particle size. ULPA (Ultra-Low Penetration Air) goes further, typically rated 99.9995% at 0.12 micron under standards such as IEST and EN 1822. These ratings are different from MERV under ASHRAE 52.2 or ISO 16890, which classify general HVAC filters. In short, MERV 13–16 improves IAQ substantially, but HEPA and ULPA are specialized for critical control of fine particles and aerosols.

How HEPA/ULPA Filters Work

Even though 0.3 micron sounds small, HEPA/ULPA filters trap particles by impaction, interception, and diffusion. That includes PM2.5, many allergens, wildfire smoke constituents, and certain bioaerosols. The key is high capture efficiency with minimal bypass leakage—any gap around the filter frame can undermine the rating.

Where They Make Sense

• Wildfire smoke mitigation and PM2.5 reduction
• Allergy- and asthma-sensitive homes and offices
• Dental/medical suites, cleanrooms, labs, and production areas
• Schools, daycares, senior living, and high-density workplaces
• Server rooms and electronics manufacturing where dust control matters

Note: For infection control or cleanroom performance, follow applicable codes and standards and consider integrity testing (PAO/DOP scanning) for HEPA/ULPA units.

HEPA/ULPA vs. High-MERV Filters

• MERV 13–16 (ASHRAE 52.2) is the practical upper end for many central air systems and aligns with ISO 16890 fine particle classes. It significantly improves IAQ for most homes and offices.
• HEPA/ULPA requires specialized housings and fans to handle higher pressure drop and sealing. They are common in healthcare, labs, and clean manufacturing, and can be deployed in residences with the right engineering.

Ways to Add HEPA/ULPA to HVAC

1) In-duct HEPA modules

These are dedicated housings installed in the supply or return. They demand adequate fan capacity, correct filter face velocity, and gasketed frames to prevent bypass leakage. Pre-filters (MERV 8–13) extend HEPA life.

2) Bypass HEPA systems

A portion of air is routed through a separate HEPA cabinet with its own fan, then returned to the duct system. This reduces the load on the main air handler and allows continuous filtration without over-restricting airflow.

3) Dedicated HEPA air handlers

Independent HEPA units serve critical rooms with controlled air changes per hour (ACH). This is common in clean areas, medical suites, and high-risk applications.

4) Portable HEPA units

Portable HEPA purifiers can supplement central HVAC, especially during wildfire smoke events. They do not replace proper HVAC engineering but can add clean air delivery rate (CADR) where needed.

5) Mini-splits and ductless systems

Most mini-splits cannot accept true HEPA in the indoor head due to pressure drop. Options include inline HEPA boxes on ducted mini-split air handlers, room-side HEPA units, or pairing with balanced ventilation (ERV/HRV) and high-MERV pre-filters.

Engineering Factors That Matter

• Static pressure and pressure drop: HEPA/ULPA adds resistance. Verify fan curves, motor capacity, and duct design so airflow and comfort are maintained.
• Sealing and housings: Use gasketed frames and tested housings to prevent bypass leakage. The best filter can underperform if air sneaks around it.
• Air changes per hour (ACH): Match filter area and fan speed to IAQ targets, occupancy, and room size.
• Energy and noise: Higher resistance can raise energy use and sound levels; right-sizing and pre-filtration help.
• Monitoring: Differential pressure gauges indicate filter loading and replacement timing.

Maintenance and Replacement

Plan for scheduled replacement based on differential pressure and use patterns. Use staged pre-filters (MERV 8–11 or MERV 13) to intercept larger particles, extending HEPA/ULPA life. In critical environments, consider periodic integrity testing. Always replace with rated, certified media in compatible housings.

Safety, Compliance, and Insurance Considerations

Improperly adding HEPA/ULPA to HVAC can cause equipment strain, overheating, noise, comfort issues, and IAQ backfires from bypass leakage. In some occupancies, local codes, AHJ approvals, or documentation may apply. Many insurance carriers and facility policies require licensed, qualified specialists for design, installation, and maintenance, especially in healthcare or clean processes. DIY shortcuts can void warranties, create safety risks, or fail inspections.

When HEPA/ULPA Is Overkill—and Smart Alternatives

• For most homes and many offices, MERV 13–16 plus source control and ventilation (ERV/HRV) can meet IAQ goals at lower cost and complexity.
• Use portable HEPA units during wildfire smoke surges or seasonal allergies to boost clean air delivery without permanent duct changes.
• Measure IAQ (PM2.5, CO2, humidity) to guide choices and confirm results.

About #1 AC Guys

#1 AC Guys is a fourth-generation family of engineers serving Los Angeles County and nearby areas, including Orange County, Ventura County, and Western Riverside County. With 80+ years of engineering experience, we focus on complex residential and commercial projects and our mission is simple: healthy air at home for a healthy life. Our engineers have trained at manufacturer facilities: Fujitsu (Japan), Mitsubishi Elektrik (Thailand), Midea (China), Gree (China), and Hier (China).

Typical Service Areas

We work across Los Angeles County and nearby regions, including cities such as Los Angeles, Long Beach, Santa Monica, Pasadena, Glendale, Burbank, Anaheim, Irvine, Santa Ana, Huntington Beach, Fullerton, Thousand Oaks, Oxnard, Ventura, Camarillo, Riverside, Corona, and Murrieta.

Key Takeaways

1. HEPA is 99.97% at 0.3 micron; ULPA is 99.9995% at 0.12 micron.
2. They outperform high-MERV filters but require proper housings, sealing, and fan capacity.
3. Consider wildfire smoke, allergies, healthcare, and clean processes for HEPA/ULPA use.
4. Design to manage static pressure, pressure drop, and bypass leakage; verify with ASHRAE 52.2/ISO 16890 context and IEST/EN 1822 where applicable.
5. Professional design and installation are often necessary and may be required by insurance or local authorities.