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  3. Reverse-Flow Exhaust Fan Filter Unit (FFU)

Reverse-Flow Fan Filter Unit (for Particle-Free Exhaust)

exhaust fan/filter units
Removes microcontaminants generated inside an enclosure

Models with adapter housing feature 12”-diameter flange for ducting of hazardous materials (shown: No. 6601-24-HVF)
canada and us Ul logo CE logo
Models below are UL and UL-Canadian listed.
CE marked models available; inquire when ordering.

Optional Challenge Port
simplifies leak testing

Explosion-Proof, all-stainless steel reverse-flow models also available.
  • Removes submicron particles generated inside a cleanroom or equipment enclosure
  • Ideal for removing dust generated inside an enclosure before release of exhaust air
  • Select HEPA filter (99.99% efficient @ 0.3 µm particles) or ULPA filter 999.999% efficient @ 0.12 µm particles)
  • Low-profile design allows installation on cleanrooms with standard 9-foot ceilings
  • Quiet, low-vibration WhisperFlow™ design: only 50 dBA, measured 30” from filter face @ 90 FPM
  • Provides an airflow of 640+ CFM under filter load at medium speed (2’ x 4’ model)
  • Three-speed switch provides simplified air balancing
  • Provides years of no-maintenance, 24/7 operation depending on your air quality

The Reverse-Flow WhisperFlow Fan Filter Units (FFUs) are ideal for removing sub-micron particles, aerosols and fine dust generated inside an enclosure, allowing safe release of HEPA- or ULPA-filtered air. They are perfect for hoods, enclosures and modular cleanrooms that contain operations that produce particles unsuitable for exhausting into the surround space.

The HEPA filter option safely removes micro-contaminants down to 0.3 µm and the ULPA filter option removes particulates down to 0.128 µm.

All models use a 3-speed fan/motor with permanently lubricated bearings mounted inside a white powder-coated steel housing. Models are available with 12"-diameter flanges to allow ducting of fumes and particles removed from an enclosure.

Related Product: Smart WhisperFlow Fan Filters Units

Ordering Information
All models below include a HEPA or ULPA filter that features an anodized aluminum frame and filter face grille. For highly sterile operations, an all-stainless steel filter is available, which features a 304 stainless steel filter frame and face grille that stand up better to alcohol and other cleaning agents. Ask your Terra sales representative for a quotation with current lead time on all-stainless steel FFUs.

Standard Reverse-Flow Models without Flange Adapter Housing (all are 13"H)

Reverse-Flow Fan Filter Unit: Powder-Coated Steel
Filter Size /Feet Power With HEPA Filter With ULPA Filter
Cat. # Price Cat. # Price
2’ x 4’ 120VAC 6601-24-HV $ 1,137 6601-24-UV $ 1,263
2’ x 4’ 220VAC 6601-24-HV-220 $ 1,251 6601-24-UV-220 $ 1,263
2’ x 3’ 120VAC 6601-23-HV $ 1,137 6601-23-UV $ 1,263
2’ x 3’ 220VAC 6601-23-HV-220 $ 1,251 -- --
2’ x 2’ 120VAC 6601-22-HV $ 1,137 6601-22-UV $ 1,263
2’ x 2’ 220VAC 6601-22-HV-220 $ 1,251 6601-22-UV-220 $ 1,263
Reverse-Flow Fan Filter Unit: 304 Stainless Steel
Filter Size /Feet Power With HEPA Filter With ULPA Filter
Cat. # Price Cat. # Price
2’ x 4’ 120VAC 6601-24-HVSS $ 1,595 6601-24-UVSS $ 1,699
2’ x 4’ 220VAC -- -- -- --
2’ x 3’ 120VAC -- -- 6601-23-UVSS $ 1,699
2’ x 3’ 220VAC -- -- -- --
2’ x 2’ 120VAC -- -- 6601-22-UVSS $ 1,699
2’ x 2’ 220VAC -- -- -- --

Reverse-Flow Models with 12”-diameter Exhaust Flange Adapter Housing(all are 21"H)

Reverse-Flow Fan Filter Unit: Powder-Coated Steel
Filter Size /Feet Power With HEPA Filter
Cat. # Price
2’ x 4’ 120VAC 6601-24-HVF $ 1,418
2’ x 4’ 220VAC 6601-24-HVF-220 $ 1,560
2’ x 3’ 120VAC 6601-23-HVF $ 1,418
2’ x 3’ 220VAC 6601-23-HVF-220 $ 1,560
2’ x 2’ 120VAC 6601-22-HVF $ 1,418
2’ x 2’ 220VAC 6601-22-HVF-220 $ 1,560
Reverse-Flow Fan Filter Unit: 304 Stainless Steel
Filter Size /Feet Power With ULPA Filter
Cat. # Price
2’ x 4’ 120VAC 6601-24-UVFSS $ 1,837
2’ x 4’ 220VAC -- --
2’ x 3’ 120VAC 6601-23-UVFSS $ 1,837
2’ x 3’ 220VAC -- --
2’ x 2’ 120VAC 6601-22-UVFSS $ 1,837
2’ x 2’ 220VAC -- --

Filter Replacement Alarm System

This optional module monitors the efficiency of the HEPA filters and alerts personnel when the HEPA filters need to be replaced. The module's Photohelic gauge connects to the nearest Fan/Filter Unit equipped with a Challenge Port (Part # 6601-99) and displays the backpressure created within the FFU.

Filter Replacement Alarm System

As the HEPA filter accumulates particles over its lifetime, pressure builds in the space between the blower and the HEPA filter. The Photohelic gauge features two manually adjustable needles that are used to mark the original backpressure reading and the maximum acceptable level (which is typically double the backpressure reading of a new filter). When the backpressure exceeds this set limit, the LED indicator light located above the gauge will flash and a buzzer will sound, notifying personnel that the room's HEPA filters should be replaced. An override switch silences the buzzer, but the light continues to flash until the filter is replaced.

If a HEPA filter accumulates too many particles and becomes clogged, it can result in a loss of efficiency that can compromise the cleanroom's ISO rating. If they are not replaced in a timely manner, severely clogged filters can destroy the motors in the Fan/Filter Units and potentially pose a fire hazard in the event of catastrophic electrical failure.

  Cat. # Price
Filter Replacement Alarm System 2625-54B-SS $ 1,140

FFU Challenge Port

Air filters keep your environment clean, but validating their integrity can be cumbersome and knowing when to replace them is a challenge. Room designs, applications and staffing make each cleanroom unique. Therefore, it’s important to get baseline measurements of your equipment when first installed, and then set up a schedule for regular monitoring.

Tubing fits into both the orange challenge port valve and the Magnehelic® gauge to easily record FFU pressure differential.
Upgrade your fan/filter unit (FFU) to include a Terra-installed Challenge Port that both simplifies leak testing and helps establish a filter replacement schedule. The port is 3/8"-diameter, nickel-plated brass adapter fitting with a white polypropylene plug.

Learn more about Terra's FFU Challenge Port.

Price includes installation on specified FFUs.

FFU Challenge Port
Cat. # Price
6601-99 $ 67

Cord Adapter
Connect your Terra Fan/Filter Unit directly to a wall outlet using this 3-foot cord adapter. FFUs are built with a 4-pin electrical connector for integration with a power module in a modular cleanroom or laminar flow hood. This adapter allows you to bridge the power connection when a power module is not used. Simply plug the 4-pin connector, that terminates in a NEMA 5-15 plug for connection, into the FFU power cord and fit the other end into a standard power outlet.

  Cat. # Price
Cord Adapter (4-pin) 120VAC, 60Hz 6601-13 $ 50

Ceiling-Module Mounting Frame
Stainless steel mounting frames allow ceiling modules to be installed in drywall or other hard ceilings without a ceiling grid.* The frames are sized to hold 2' x 4' fan/filter units or light panels, or 2' x 3' and 2' x 2' fan/filter.

Frames "cradle" the modules, and sit securely in the ceiling cut-out with support from top flange. Continuous seams in the 304 stainless steel frames' corners reduce deposit of contaminating particles and simplify cleaning.
FFU Mounting Frame
FFU Mounting Frame FFU Mounting Frame
Shown with Fan/Filter Unit installed, viewed from above ceiling panel. Ceiling module mounting frame:
2' x 4' shown (Cat. no. 6604-02), holding fan/filter
unit or light panel.
Description Cat. # Price
Mounting Frame: 2' x 4' 6604-02 $ 269
Mounting Frame: 2' x 3' 6604-01 $ 261
Mounting Frame: 2' x 2' 6604-00 $ 254
* Intended for use with supported ceilings that can safely bear the weight of fan/filter unit or light being installed. Mounting frame provides no support beyond the perimeter of the ceiling cut-out.

Terra FFU Replacement Filters
Type Filter Size / Feet (mm) Aluminum Frame
with Andodized Aluminum
Face Grille
304 Stainless Steel
with SS Face Grille
Cat. # Price Cat. # Price
HEPA 2 x 2 (610 x 610)
6601-27 $ 330 6601-27-S Call TUI
2 x 3 (610 x 914)
6601-26 $ 395 6601-26-S $ 557
2 x 4 (610 x 1219)
6601-25 $ 397 6601-25-S $ 552
ULPA 2 x 2 (610 x 610)
6601-30 $ 340 6601-30-S $ 640
2 x 3 (610 x 914)
6601-29 $ 407 6601-29-S $ 770
2 x 4 (610 x 1219)
6601-28 $ 408 6601-28-S $ 834

File Type File Name Publication Date
Tech Resource (PDF) HEPA and ULPA Particle Filters
HEPA and ULPA filters remove sub-micron particles from the air, which are too small to see but create BIG problems in many critical manufacturing operations. Read about filter capability and airflow resistance testing.
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