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Stainless Steel WhisperFlow® Fan/Filter Units (FFUs)

Stainless Steel Whisper Flow FFU
Stainless Steel Fan/Filter Unit, showing power cord that connects to Power Distribution Module.

cULus logo Wafer/CE

Models below are UL and UL-Canadian listed. CE marked models available; inquire when ordering

Optional Challenge Port
simplifies leak testing
  • BioSafe 304 stainless steel housing meets requirements for cleanliness and chemical compatibility
  • Internal baffling plates and diffuser panel provide uniform air speed across the filter face, ensuring laminar airflow
  • Low-profile design allows cleanroom installation inside rooms with standard 9-foot (2743 mm) ceilings
  • Quiet, low-vibration design: only 50 dBA, measured 30" (762 mm) from filter face @ 90 FPM (0.5 m/s)
  • Provides an average airflow velocity of 90+ feet per minute (.45+ m/sec) and airflow of 640+ CFM (1088 m³/hr) under filter load at 100% medium setting (2' x 4', 610 mm x 1219 mm, model)
  • Three-setting switch simplifies air balancing (see below for EnergySaver Remote Control System)
  • Meets IEST Recommended Practices
  • Refer to the Application Guidelines for recommendations on quantities to meet specified requirements for cleanliness and lighting.

These reliable, self-powered Fan/Filter Units provide a uniform flow of microfiltered air to meet cleanliness standards down to Class 10 (ISO 4).

All models use a 3-setting (hi/med/lo), centrifugal-type fan/motor with permanently lubricated bearings mounted inside a stainless steel housing with drop-in prefilter (stainless steel available). The HEPA or ULPA filter is mounted in a 304 stainless steel frame with stainless steel filter face grille; powder coated housing is available.

Advanced baffling technology ensures uniform airflow across the filter face and attenuates sound. Select HEPA (High-Efficiency Particulate Air) filters, rated 99.99% efficient at removing particles ≥ 0.3 microns, or ULPA (Ultra-Low Penetration Air) filters, rated 99.9995% efficient at removing particles ≥ 0.128 microns. They provide years of no-maintenance, 24/7 operation, depending on your air quality.

All prices below include installation on a specified Terra modular cleanroom.

Roomside replaceable FFU
Automated FFU control systems help meet FDA and other compliance regulations. Add options including environmental monitoring and data logging. Click for details
BioSafe 304 Stainless Steel Roomside
Replaceable models
also available

Related Product: Smart WhisperFlow Fan Filters Units

Ordering Information
BioSafe 304 Stainless Steel Fan / Filter Units with HEPA Filter
Model Nominal
@ MS
Airflow ft/min(m/s) Run Amps (Watts)
@ 60Hz
Power With
HEPA Filter
HS MS LS HS MS LS Cat. # Price
2 x 4 23.63 x 47.63 x 13
(600 x 1210 x 332)
120VAC, 60 Hz 6601-24-HSS $ 1,376
220VAC, 60 Hz 6601-24-HSS-220 $ 1,514
2 x 3 23.63 x 35.63 x 13
(600 x 905 x 332)
120VAC, 60 Hz 6601-23-HSS $ 1,376
2 x 2 23.63 x 23.63 x 13
(600 x 600 x 332)
120VAC, 60 Hz 6601-22-HSS $ 1,376
220VAC, 60 Hz 6601-22-HSS-220 $ 1,514
* With pre-filter installed. Nominal height of CE-marked units is 13.5" (343mm).

Dimensions: See Replacement Filter chart
Housing: Plenum is 304 stainless teel. Compatible with 1-1/2" (38 mm) grid on 24" x 48" (610 mm x 1219 mm) centers or 2" (51 mm) grid on 24.5" x 48.5" (622 mm x 1232 mm) centers
HEPA Filter: HEPA filter is 99.99% efficient on removal of particles 0.3 microns and larger by DOP (dioctyl phthalate) test. Filter module must be removed from the ceiling for HEPA filter replacement
Prefilter: 20" x 20" x 1" (508 mm x 508 mm x 25 mm)– UL classified for Class 1; rated 80% efficient on linty dusts
Blower: Forward-curved centrifugal type factory balanced. Entire motor/blower assembly is removable from top of housing for service
Motor: 1/4 HP Direct drive, energy efficient. Permanent split capacitor type. Thermally protected with automatic overload reset
Electrical: 3-setting motor switch (lo-med-hi). Motor leads are wired to a cable with Mencom 4-pin connector for field connection to Terra cleanrooms and hoods; specify other required power cable
Face Grille: 304 stainless steel
Noise Level: 50 dBA
Weight: See Ordering charts
Support: 1/4" (6 mm) eyebolts are installed in all (4) corners for hangwire support

FFU Accessories

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

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

Night Service Switch
  • Energy-saving mode saves 25% of fan operating costs by reducing power consumption during off-hours
  • Maintains round-the-clock cleanroom integrity at lower cost
  • Easy to activate via panel-mounted switch (Wireless Cleanroom Control System also available)

Why Pay More for Less?
Terra cleanrooms are designed to meet a specified ISO cleanliness rating when a cleanroom is in use: with operations in progress, process machinery humming, and personnel in motion. So why pay to maintain that level of FFU performance when a production shift ends and people, the greatest source of contamination, leave the room?

With a greatly reduced contaminant load, a cleanroom at rest maintains its target ISO cleanliness standard with much less airflow, fewer air changes—and decreased power consumption. Terra’s Night Service Switch provides this cleanliness at a nominal cost, giving you immediate cost savings.

Simply select the “Night Service" Switch when you turn off the lights and go home. A separate operation circuit drops all Fan/Filter Units (FFUs) into low-energy operation mode, shaving 25% of energy costs off your power bill while maintaining uninterrupted cleanroom performance at your specified cleanliness level. With Terra's Night Service Switch, operators can save up to 7,000 kilowatt-hours per year with a return on investment in slightly over a year.**
Ordering Information
A complete system includes fan/filter units and Terra's standard Power Distribution Modules (order separately), in addition to the units specified below. The Night Service Switch includes electronic configuration of each FFU controlled by this system. The Control Panel includes switch settings and indicator lights for Normal Mode and Night Service Mode, as well as a tamper-resistant master FFU Off switch.
Night Service Switch
Order one per Fan Filter Unit Cat. # Price
120VAC, 60Hz 6601-70 $ 120
Control Panel for Night Service Switch
Order one per cleanroom 120VAC, 60Hz 220VAC, 60Hz
Cat. # Price Cat. # Price
Hardwall Cleanroom, External Mount Panels 6600-23-NS $ 2,039 6600-23-NS-220 $ 2,039
Hardwall Cleanroom, Internal Mount Panels 6600-24-NS Call TUI 6600-24-NS-220 Call TUI
Softwall Cleanroom 6600-25-NS $ 1,906 6600-25-NS-220 $ 1,906
BioSafe All-Steel Cleanroom 6600-26-NS $ 2,039 6600-26-NS-220 $ 2,039
BioSafe FRP/C-PVC Cleanroom 6600-57-NS Call TUI 6600-57-NS-220 Call TUI
Comparative Specifications:
2’ x 4’ (600 x 1210 mm) Terra Fan/Filter Unit No. 6601-24-H, operating at High, Medium, and Night Service setting
Operation Setting: High Speed* Medium Speed* Night Service
Airflow: cfm (m^3/hr) 808 (1373) 717 (1218) 654 CFM (1111)
Air Speed: ft/m (m/s) 115 (0.58) 102 (0.51) 93 ft/min (0.47)
Run Amps (Watts): 4.3 (512) 3.5 (416) 3.3A (393W)*
*25% savings over operation on high speed
**Based off of an average-sized cleanroom with 10 FFUs, active cleanroom usage of 8 hours per day, and the U.S. Energy Information Administration's given average retail price of electricity at 10.72 cents per kilowatt-hour.

Ionizing Bar
Eliminates surface charges generated by laminar flow for a cleaner cleanroom

IonBar™ Ionizing Bar with FFU Installation Kit

The IonBar generates a balanced stream of positive and negative ions to neutralize surface static charges, protecting sensitive parts against ESD and eliminating surface attractions that make cleaning difficult. Its low-voltage design is intrinsically safe and minimizes EMI/RFI. Includes installation kit for easy attachment to fan/filter units (order separately), which disseminate ions throughout the cleanroom.

For FFU Size
Fett,No. of emitters
For 120VAC,
For 220VAC,
50/60 Hz
Cat. # Price Cat. # Price
2 x 4, 8
(610 x 1219)
2005-49 $ 781 2005-49-220 $ 790
2 x 3, 6
(610 x 914)
2005-48 $ 681 2005-48-220 $ 693
2 x 2, 4
(610 x 610)
2005-47 $ 569 2005-47-220 $ 603
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
Shown with Fan/Filter Unit installed, viewed from above ceiling panel. Ceiling module mounting frame:
2' x 4' shown, 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.

File Type File Name Publication Date
White Paper (PDF) Airflow Uniformity and Fan Filter Units
Fan filter units help to remove contaminants from controlled environments. They are effective if designed well. Variables like speed and baffles contribute to an FFU's ability to maintain uniform air speed and direction. Read more about how FFUs help you comply with ISO and other regulations.
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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