If you're replacing the HEPA filter in a negative air machine or air scrubber and you've measured 24 inches by 24 inches by 11.5 inches — you're holding the most common commercial HEPA filter size in the construction and remediation industry. But knowing the dimensions is only step one. The frame material, efficiency grade, and capacity rating determine whether your machine passes inspection, meets ICRA or OSHA requirements, and keeps running at full CFM through a demanding jobsite.

This guide answers the most common question contractors ask us: which machines actually take a 24x24x11.5 HEPA filter, and which specific filter do I need for my application? We've mapped every compatible machine Spycor.com carries to the right filter for the job.

What Is a 24x24x11.5 HEPA Filter — And Why Is It the Industry Standard?

The 24" x 24" x 11.5" dimension (sometimes written as 24x24x11½ or 24x24x12) is the universal standard size for commercial-grade HEPA filters used in portable negative air machines and air scrubbers. The 11.5-inch depth is critical — it accommodates the deep-pleat media pack required to achieve true HEPA efficiency (99.97% or higher) at the high airflow rates these machines demand, typically 600 to 2,000 CFM.

Machines in this class are the workhorses of healthcare construction, abatement, and remediation. They create negative pressure in a contained work zone, exhaust contaminated air through a HEPA filter, and prevent dust, mold spores, asbestos fibers, silica particles, and other hazardous airborne contaminants from migrating into occupied areas.

Air Scrubbers & Negative Air Machines That Use This Filter Size

The following machines carried by Spycor Environmental all accept a standard 24x24x11.5 HEPA filter as the primary filtration stage. Always verify the filter slot dimensions in your owner's manual before ordering — some units have slight tolerances that affect fit.

1. OmniAire OA2200C — 2,000 CFM Workhorse for Abatement

The OmniAire OA2200C is the most widely deployed negative air machine in commercial abatement and mold remediation in the U.S. Running at 1,000 to 2,000 CFM with a certified 99.99% HEPA final stage, it is the machine most contractors picture when they search for a 24x24x11.5 HEPA replacement filter. The OA2200C uses a three-stage filtration system: a washable primary prefilter, a 95% efficiency secondary filter, and the main 24x24x11.5 HEPA final filter.

Recommended filter: NC Filtration 99.97% Particle Board or Koch BioMAX 99.97% Galvanized Steel for high-humidity abatement environments.

Click Here to Shop OmniAire OA2200C

2. OmniAire OA600N Nitro — Healthcare & Commercial Environments

The OmniAire Nitro runs at 200 to 1,000 CFM with a built-in HEPA filtration system and integrated air scrubbing. It is designed for environments where quiet operation and clean-air recirculation matter more than raw CFM — hospitals, occupied office buildings, schools, and clinics. The Nitro's 99.99% HEPA final stage uses the standard 24x24x11.5 footprint, making filter replacement consistent with the rest of your fleet.

Recommended filter: Glasfloss Magna 99.99% Wood Frame — moisture-resistant media that will not support microbial growth, ideal for healthcare environments.

Click Here to Shop OmniAire Nitro 

3. Rental A600 Air Scrubber — ICRA-Compliant, Occupied Healthcare

The Rental A600 is Spycor.com's dedicated occupied healthcare air scrubber, available exclusively for rent and certified for ICRA-compliant hospital renovation projects. It runs at 300 to 600 CFM with individually tested and certified 99.99% HEPA filters. Each unit is inspected before rental to verify filter integrity and seal. If you are renting this unit, Spycor.com ensures the filter is replaced between rentals — but contractors who own similar machines should replace filters after every project involving ICRA Class IV or V environments.

Note: This unit is for occupied healthcare facilities only and is NOT approved for asbestos remediation work.

Click Here to Shop Rental A600 

Which 24x24x11.5 HEPA Filter Do You Need? The Complete Spycor.com Lineup

Not all 24x24x11.5 HEPA filters are interchangeable. The frame material, efficiency rating, and capacity class determine compliance, performance, and cost-per-job. Here is every filter Spycor.com stocks in this size, with a clear recommendation for each application.

Filter 1: NC Filtration 99.97% Standard-Capacity — Particle Board Frame

The go-to filter for everyday construction, mold remediation, asbestos abatement, and dust control. Built with 5/8" particle board framing that is glued and stapled for rigidity. The media is a single continuous sheet of high-strength waterproof glass microfiber paper with corrugated aluminum separators between each pleat to maintain airflow. Fire-retardant rubber and urethane sealants provide a positive seal at the frame, and a closed-cell neoprene gasket on the downstream face prevents air bypass.

• Efficiency: 99.97% at 0.3 microns — meets minimum HEPA standard for OSHA and EPA RRP compliance
• Frame: Particle board — cost-efficient for high-dust jobs requiring frequent replacement
• Best for: Mold remediation, asbestos abatement, general construction, lead paint RRP jobs
• Price point: Most affordable 24x24x11.5 HEPA option in Spycor.com's lineup

Click Here to Shop NC Filtration 99.97% Particle Board

Filter 2: Koch BioMAX 99.97% — Particle Board Frame

The Koch BioMAX line is the premium brand standard for hospital and pharmaceutical facility managers who need a name-brand filter for compliance documentation. Available in standard and high-capacity configurations. The high-capacity BioMAX HC contains approximately 50% more filter media than the standard model, extending filter life and reducing change-out frequency on continuous-duty machines.

• Efficiency: 99.97% at 0.3 microns (99.99% and 99.999% ULPA versions also available)
• Frame: Particle board (UL Class 2) — easy disposal in construction waste streams
• Best for: Hospital GCs, pharmaceutical contractors, facilities teams needing documented brand compliance
• High-capacity model: Rated for up to 2,000 CFM — pairs directly with OA2200C and OA2200UL

Click Here to Shop Koch BioMAX 99.97% Particle Board

Filter 3: Koch BioMAX 99.97% — Galvanized Steel Frame

The steel-frame BioMAX is the right choice when your jobsite involves high humidity, steam, chemical vapors, or situations where a wood or particle board frame could swell, warp, or absorb moisture. The 18-gauge galvanized steel cell sides (UL Class 1) resist corrosion and provide dimensional stability in wet environments. If you are running a negative air machine in a flood remediation project, a boiler room, or a commercial kitchen renovation, this is your filter.

• Efficiency: 99.97% at 0.3 microns
• Frame: Galvanized steel (UL Class 1) — withstands moisture, chemicals, and high-pressure cleaning
• Best for: Water damage restoration, high-humidity environments, chemical exposure, permanent HVAC integration
• Note: Steel frame disposal may require separation from organic construction waste — check local regulations

Click Here to Shop Koch BioMAX 99.97% Galvanized Steel

Filter 4: Glasfloss Magna 99.99% — Wood Frame, High-Capacity

The Glasfloss Magna 1100 Series operates at 99.99% efficiency — one full grade above standard HEPA — making it the correct filter for ICRA Class IV and V hospital renovation projects where infection control protocols demand maximum particle capture. The moisture-resistant glass microfiber media will not support microbial growth, a critical compliance requirement in occupied healthcare facilities. The high-capacity configuration handles higher airflow with lower pressure drop, extending motor life on continuous-duty machines.

• Efficiency: 99.99% at 0.3 microns — exceeds ICRA Class IV minimum requirements
• Frame: Wood — rigid, seals cleanly with neoprene gasket, lower cost than metal
• Best for: Hospital GCs under ICRA Class III-IV-V, pharmaceutical cleanrooms, biotech labs
• Media: Moisture-resistant — will not support microbial growth per Glasfloss QA program

Click Here to Shop Glasfloss Magna 99.99% Wood Frame

Filter 5: Glasfloss Magna 99.99% — Metal Frame, High-Capacity

The top-of-line 24x24x11.5 HEPA option for permanent HVAC installations, cleanrooms, and environments where filters are cleaned in place rather than discarded after each project. The 18-gauge galvanized metal frame withstands continuous temperatures up to 180°F, making it compatible with high-temperature air handling units. The rolled-edge aluminum separators prevent media chafing during handling and extend media life in high-velocity applications.

• Efficiency: 99.99% at 0.3 microns
• Frame: 18-gauge galvanized metal — rated to 180°F continuous operating temperature
• Best for: Permanent HVAC cleanroom applications, pharmaceutical manufacturing, aerospace, high-temp environments
• Capacity: High — optimized for low pressure drop at elevated airflow velocities

Click Here to Shop Glasfloss Magna 99.99% Metal Frame

How to Choose the Right 24x24x11.5 HEPA Filter for Your Job

Use this decision framework before ordering. Matching the wrong filter to your jobsite can cause compliance failures, reduced machine performance, and costly downtime.

When to Replace Your 24x24x11.5 HEPA Filter

The most common mistake contractors make is running a HEPA filter too long. A clogged filter reduces CFM output — which means your machine is no longer creating adequate negative pressure, and contaminated air may be escaping containment. Replace your filter when any of the following occur:

• The filter change indicator light or gauge activates (most OmniAire and BioMAX machines have this)
• Machine CFM drops more than 10-15% from rated output
• At the end of every ICRA Class IV or V hospital project — regardless of hours of use
• After any asbestos or lead abatement project — contaminated filters are regulated waste
• Every 3-6 months in continuous-duty commercial HVAC applications
• Whenever the filter shows visible damage, tears, or bypass around the gasket seal

Shop All 24x24x11.5 HEPA Filters at Spycor Environmental

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Frequently Asked Questions: 24x24x11.5 HEPA Filters

Is 24x24x11.5 the same as 24x24x12?

Yes, in most cases. The nominal size listed as 24x24x12 and the actual dimension of 24x24x11.5 refer to the same filter category. The 0.5-inch difference is a standard manufacturing tolerance. Always verify the actual slot dimensions in your machine's owner's manual before ordering.

Can I use a 99.97% filter in a machine rated for 99.99%?

Technically the filter will fit, but you will not meet ICRA Class IV or V compliance requirements if your project mandates 99.99% or higher filtration. For OSHA abatement, asbestos, and mold remediation, 99.97% is the minimum standard. For occupied healthcare facilities, always use 99.99% or better.

What is the difference between standard capacity and high-capacity (HC)?

A high-capacity filter contains approximately 50% more filter media than a standard model, allowing it to handle higher airflow rates (up to 2,000 CFM) with lower pressure drop. Use HC filters in machines running at or near maximum CFM. Standard capacity filters are suitable for machines running at 600-1,000 CFM or lower.

Do I need a special filter for asbestos vs. mold remediation?

Both require a minimum 99.97% true HEPA filter. However, used filters from asbestos abatement projects are classified as regulated asbestos-containing material (RACM) and must be disposed of according to EPA NESHAP and local regulations. Mold remediation filters follow standard construction waste guidelines in most jurisdictions, but check your local environmental regulations.

Can I buy 24x24x11.5 HEPA filters in bulk for contractor pricing?

Yes. Spycor Environmental offers bulk pallet pricing and contractor accounts for companies that regularly replace multiple filters per project. Contact Spycor.com directly at 1-877-293-0784 to discuss volume pricing, standing purchase orders, and contractor account setup.