Mist Eliminator Filters — Washable Aluminum, Stainless Steel & Galvanized

HM Series Mist Eliminator Filters — Shop by Alloy and Size

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Product Overview — How Mist Eliminator Filters Work

Standard air filters are designed to capture dry airborne particulate by mechanical interception, impaction, or diffusion. Mist eliminators solve a different problem: removing the fine liquid droplets — water, condensate, oil mist, salt spray — that are carried in suspension in a fast-moving airstream. These droplets are too heavy to stay airborne under reduced velocity but too small and numerous to be stopped by gravity alone before reaching downstream equipment. Left unaddressed, entrained moisture accelerates coil corrosion, promotes biological growth in air handling units, contaminates process air streams, and causes premature failure of electronic components in data center and industrial control enclosure applications.

The HM Series uses a multi-ply corrugated or crossed-layer metal mesh media pack. As the airstream passes through the media, it is forced through a tortuous path of narrow channels and directional changes. Droplets larger than approximately 3 to 10 microns cannot follow the air around these curves — they continue in a straight line, impact the media surface, and adhere. As more droplets land and coalesce on the same fiber surface, they grow into larger drops, become too heavy to be re-entrained by the airflow, and drain by gravity down the media face and out through the corner drain holes in the filter frame. The result is a drained, substantially drier airstream leaving the filter face.

Because the separation mechanism is physical rather than chemical, the media does not degrade or lose efficiency when wet — in fact, a slightly wetted media surface improves coalescence performance. This makes the HM Series suitable for constant-duty applications where moisture loading is continuous rather than intermittent. The metal construction (aluminum, 304 stainless steel, or galvanized steel) withstands the operating temperatures, cleaning cycles, and corrosive airstream conditions that would destroy foam or fiberglass media alternatives.

Three media depth options serve different application requirements. The 1” depth provides a compact, low-pressure-drop solution for space-constrained installations and moderate-humidity outdoor air intakes. The 2” depth doubles the coalescence path length for heavier moisture loads — coastal environments, cooling tower intake air, and light industrial mist applications. The 4” depth is specified for heavy-duty industrial environments including machine shop oil mist extraction, offshore platform HVAC, marine vessel ventilation, and chemical plant air handling units where continuous high-concentration liquid aerosol loading is expected.

Technical Specifications

All HM Series mist eliminator filters are manufactured to the following specifications. Values apply across all alloy options and standard depths unless noted.

Applications — Where Mist Eliminator Filters Are Used

Mist eliminator filters are specified wherever an airstream carries entrained liquid that must be removed before the air contacts downstream equipment, processes, or occupied spaces. Common applications span commercial HVAC, industrial process air handling, and marine and offshore environments.

Coastal and Marine HVAC

Buildings within several miles of saltwater — oceanfront commercial properties, coastal hotels, marine terminals, and naval facilities — draw outside air that carries salt spray and fine salt aerosol. Salt-laden air is one of the fastest-acting accelerants of HVAC coil corrosion and refrigerant line degradation. An HM Series mist eliminator installed at the outside air intake intercepts salt droplets before they reach the evaporator coil, substantially extending coil service life and reducing the frequency of coil cleaning and fin repair. Stainless steel construction is the standard specification for true marine and offshore applications; aluminum is appropriate for most coastal commercial installations.

Industrial Air Handling — Oil Mist and Coolant Mist

Machine shops, CNC manufacturing facilities, metal fabrication operations, and automotive assembly plants generate oil mist and metalworking fluid aerosols as a byproduct of cutting, grinding, and forming operations. This mist migrates throughout the facility and enters HVAC return air streams, where it deposits on heat exchanger surfaces and fouls filters rapidly. The 4” depth HM Series in 304 stainless steel or galvanized steel is the standard specification for these environments, providing both the coalescence path length and the chemical resistance required for in-exhaust oil mist duty. Corner drain holes allow captured oil to drain continuously without saturating the media.

Cooling Tower and Evaporative Cooler Air Intakes

Cooling towers and evaporative coolers produce a visible plume of water vapor and fine water droplets in the discharge air. When this discharge air is re-entrained into nearby outside air intakes (a common occurrence in rooftop equipment layouts), the downstream HVAC equipment receives air with elevated moisture content far above ambient humidity. An HM Series mist eliminator at the outside air intake captures this re-entrained plume moisture before it wets downstream components, maintains designed supply air conditions, and prevents biological growth associated with continuously wet internal surfaces.

Food Processing and Pharmaceutical

Clean room environments and food processing facilities use mist eliminators in both supply air and exhaust air streams. In supply air applications, the mist eliminator protects the clean room or processing environment from moisture introduced by high-humidity outdoor air. In exhaust applications, it captures process moisture and fine aerosols before they enter recirculation or exhaust systems. 304 stainless steel construction is standard for these environments due to the cleaning and sanitizing protocols required in food and pharmaceutical facilities.

Data Centers and Electrical Enclosures

Data centers using outside air economization in humid climates, and electrical control enclosures in outdoor or industrial installations, use mist eliminators to prevent liquid water ingestion that could cause equipment failure. In these applications, the 1” aluminum depth is generally specified — it provides effective moisture separation with minimal pressure drop penalty, which is critical in low-static-pressure enclosure cooling applications.

Choosing the Right Alloy and Depth

Three alloy options and three depth configurations produce nine standard HM Series variants. Selecting the correct combination requires matching the media alloy to the airstream chemistry and the depth to the moisture load.

Installation Instructions

HM Series mist eliminator filters install in standard filter tracks, side-access housings, built-up filter banks, and custom duct sections. The installation procedure is similar to a standard washable mesh filter with two critical additions: drain hole orientation and downstream drainage provision.

Before You Begin

• Confirm the filter dimensions match the housing track opening. Mist eliminators require a tight face seal to prevent moisture-laden air from bypassing the media and entering the downstream section unfiltered.
• Verify that your housing or duct section has a drain provision at the bottom of the filter track. Captured liquid must have a path to exit the system. If no drain exists, install a condensate drain pan below the filter.
• Power down the air handling unit before opening access panels.
• If side gaskets were ordered, have them on hand for installation.

Step-by-Step Installation

1. Orient the filter correctly. The corner drain holes must be at the bottom of the installed filter so captured liquid can drain by gravity. Most HM Series filters are symmetric in face dimensions but the drain holes are drilled at specific corners — confirm the orientation before sliding the filter into the track.
2. Install side gaskets if applicable. If your housing track has gaps or if the application is high-moisture with zero tolerance for bypass, apply the side gaskets to the two vertical frame edges before insertion. Gaskets compress against the track walls to eliminate air bypass at the frame perimeter.
3. Slide the filter into the track with the corrugated media face toward the incoming airflow. Confirm full seating on all four sides — any gap creates an unfiltered bypass path that allows moisture to pass without contacting the media.
4. Confirm drain hole alignment. With the filter seated, verify that the corner drain holes are oriented downward and that there is a clear path for drained liquid to exit the filter housing. If the drain holes are obstructed by track walls, reposition the filter or modify the track to provide drainage clearance.
5. Close and secure the access panel. Restore power and verify normal system operation. On initial startup with a new mist eliminator, inspect the drain path after 15 to 30 minutes of operation to confirm that collected liquid is draining normally rather than accumulating in the filter frame.

Cleaning and Maintenance

HM Series mist eliminators are fully washable. Regular cleaning removes accumulated particulate, scale deposits, and dried oil residue that can reduce moisture separation efficiency over time. Unlike the media in a disposable filter, the metal mesh media does not lose structural integrity from cleaning and can be restored to near-original performance with each service cycle.

Cleaning Frequency

• Standard commercial HVAC (coastal, outdoor air): Inspect every 60 to 90 days. Clean when visible fouling is present or when system static pressure differential increases noticeably.
• Industrial oil mist applications: Inspect monthly. High-concentration oil mist can fully foul a 4” filter in 4 to 6 weeks in heavy-duty machine shop environments.
• Marine and offshore: Rinse monthly with fresh water to remove salt accumulation even when the filter appears clean. Salt buildup is not always visible but increases the media’s resistance to airflow over time.

Cleaning Procedure

1. Remove the filter from the housing. Do not clean in place — wash water contaminated with oil, salt, or industrial residue must be directed to a drain, not back into the system.
2. Flush with a garden hose or pressure washer on low setting, spraying countercurrent to the normal airflow direction to dislodge accumulated material from the media channels.
3. For oil mist fouling, apply a degreaser or commercial parts washer solution, allow a 5-minute dwell, then rinse thoroughly in both directions until runoff is clear. Ensure all degreaser residue is removed before reinstalling.
4. For scale or mineral deposits (common in cooling tower applications), a dilute citric acid or descaling solution effectively dissolves calcium carbonate buildup. Rinse thoroughly with fresh water after treatment.
5. Inspect the frame and media before reinstalling. Check for any separated corner joints, bent frame sections, or media deformation that would create a bypass gap. Straighten minor frame distortion by hand before reinsertion.
6. Reinstall following the same orientation and drain-hole-down procedure as the original installation.

Frequently Asked Questions

What is a mist eliminator filter?

A mist eliminator filter (also called a moisture separator or demister) removes entrained liquid droplets from a moving airstream. It works by forcing the air through a tortuous metal mesh media path, where droplets impact the media by inertia, coalesce into larger drops, and drain out through holes in the filter frame. Unlike standard particulate filters, mist eliminators target liquid aerosol rather than dry dust.

What is the difference between a mist eliminator and a standard air filter?

A standard particulate air filter captures dry airborne particles (dust, pollen, debris) by mechanical interception and diffusion across a fiber or mesh media bed. A mist eliminator captures liquid droplets suspended in air — water, oil mist, salt spray, coolant mist — through coalescence on metal media surfaces. The two filter types address different problems and are often used in series: a mist eliminator at the outside air intake to remove moisture, followed by a particulate filter downstream to capture dry debris.

Which alloy should I choose — aluminum, stainless steel, or galvanized?

Aluminum is the standard choice for most commercial HVAC applications: coastal buildings, outdoor air intakes, and moderate-humidity environments. It is corrosion-resistant to most airstreams, lightweight, and the most economical option. 304 stainless steel is specified for marine and offshore environments, food processing and pharmaceutical facilities, chemical plant ventilation, and any application where the airstream contains chlorides or strong acids at elevated concentration. Galvanized steel is suitable for budget industrial applications in lower-humidity environments where the zinc coating will not be attacked by the airstream chemistry.

How do I choose between 1-inch, 2-inch, and 4-inch depth?

Depth determines coalescence path length and therefore separation efficiency at a given moisture concentration. The 1” depth suits low-to-moderate humidity outdoor air intakes and space-constrained enclosure applications where pressure drop is a priority. The 2” depth is the most common commercial specification, handling typical coastal and recirculated-plume moisture loads effectively. The 4” depth is for heavy industrial duty: machine shop oil mist, marine/offshore continuous spray exposure, and any application where lower depths have been found marginal in service.

Why are corner drain holes important?

Corner drain holes are the exit point for liquid captured by the media. As the mist eliminator coalesces droplets, the collected liquid accumulates on the media surface and drains by gravity to the bottom of the filter frame. Without drain holes, this liquid pools in the frame, eventually re-enters the airstream, and the filter effectively fails to separate moisture at high loading rates. HM Series filters include corner drain holes as standard. The filter must be installed with these holes at the bottom of the installed orientation to function correctly.

Can mist eliminators remove oil mist as well as water?

Yes. The coalescence mechanism is the same regardless of the liquid chemistry — the media surface captures oil droplets by inertial impaction just as it does water droplets. Galvanized or 304 stainless steel construction is typically specified for oil mist applications due to interactions between petroleum-based oils and aluminum alloy at elevated temperatures or concentrations. The 4” depth is standard for machine shop and industrial oil mist duty. Cleaning frequency is higher in oil mist applications; a degreaser is required rather than a plain water rinse.

Are custom sizes available?

Yes. Metal Air Filters fabricates HM Series mist eliminators to exact customer-specified dimensions in all three alloys and all three standard depths. Contact us with your face dimensions (height × width × depth to the nearest 1/16”), alloy, and any special requirements (side gaskets, non-standard drain hole placement, flanged frames), and we will have a quote back to you the same business day. Browse our custom mist eliminator options for self-service sizing.

How long do mist eliminator filters last?

With regular cleaning, HM Series mist eliminators have an indefinite service life. The metal media does not degrade from wetting, drying, cleaning chemicals, or normal mechanical loading. Retire the filter if the frame develops through-corrosion (pinholes or cracks that create bypass paths), if a corner joint separates beyond re-squaring, or if the media has been physically deformed in a way that creates a persistent gap in the housing track seal.

Do mist eliminators also capture particulate?

Yes, to a degree. The metal mesh media captures coarse dry particulate by the same inertial impaction and interception mechanisms it uses for liquid droplets. However, mist eliminators are not rated for dry particulate filtration by MERV or similar standards — they are optimized for moisture separation, not particulate removal efficiency. In applications with both moisture and particulate in the airstream, the standard approach is to place a mist eliminator upstream to remove moisture first, followed by a separate particulate filter downstream to capture dry debris at its rated efficiency.

What shipping and lead times should I expect?

Standard catalog HM Series filters in stock sizes ship within 1 to 2 business days of order placement. All orders over $99 ship free. Custom-fabricated exact-dimension mist eliminators are typically shipped within 5 to 7 business days depending on size and alloy. Contact us if your project has a critical schedule requirement and we will advise on available expedite options.