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Fantech Dryer Booster Exhaust Fan Model DBF110 FR110 fan(C) InspectApedia - Fantech Clothes Dryer Exhaust Vent Draft Booster Fans
Using draft booster fans on clothes dryer vents: specifications, sources, safety

  • CLOTHES DRYER VENTING - CONTENTS: Clothes Dryer Vent Duct, Screen, & Lint Filter Installation Specification, using a Dryer Exhaust Duct Power Ventilator (DEDPV) safely.
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Clothes dryer exhaust vent draft booster fan - Dryer Exhaust Duct Power Ventilator (DEDPVs):

Some respected manufacturers recommend adding a draft booster fan (Dryer Exhaust Duct Power Ventilator (DEDPV)) on long clothes dryer vent duct runs to reduce lint accumulation and to overcome duct length restrictions, overheating, and possible fire hazards.

Yet in some circumstances the draft inducing or boosting fans may be a fire hazard themselves, and they may be prohibited in some building code jurisdictions. Shown at page top, Fantech's DBF110 dryer booster exhaust fan model DBF110. Fantech contact information is provided below.

This article series describes good practices for clothes dryer vent installation, lint traps, wall vents, filters, and screens. We include a list of clothes dryer fire safety hazards and other clothes dryer installation or maintenance mistakes that are either unsafe or that interfere with effective, economical dryer operation. We discuss types of dryer vent ducting and dryer vent doors or opening protection devices.



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Booster Fans for Long Clothes Dryer Exhaust Vent Duct Runs?

Impoper dryer booster fan installation (C) D Friedman

Dryer vent draft booster fans, permitted for sale in the U.S. & Canada, are sold to help vent dryer exhaust vent products, especially where the vent ducting has to make a long or circuitous run.

When we read that "dryer vent booster fans are illegal" or "are prohibited" I suspect some people are confusing dryer vent draft booster fans (legal, permitted), with add-on lint filters for dryers that raise safety worries (CLOTHES DRYER LINT FILTER HAZARDS). Fantech notes that

[Dryer booster fans, or Dryer Exhaust Duct Power Ventilators (DEDPV)] are [permitted for use] except in rare cases where local jurisdictions have specifically amended their own code to exclude them. The IRC has never prohibited the use of auxiliary fans to facilitate dryer exhaust, ...] - Fantech (2012)

Still, the dryer vent and draft booster fan needs to be inspected and will need periodic inspection and maintenance. The horrible dryer vent installation shown above illustrates several unsafe conditions including:

John Cranor, an ASHI home inspector, explained that booster fans are indeed permitted to help assure functional dryer vent ducts that have to extend over longer distances than the recommended 25 feet, but that the booster fan should be located at least 15 feet from the clothes dryer outlet to avoid risking drawing wet lint into and clogging the clothes dryer vent fan.[8]

According to Tjernlund, a manufacturer of several types of draft inducer fan systems, "The Dryer Duct Booster can also reduce the potential fire hazard associated with lint buildup." [9]. Excerpt

Clothes dryers are often installed in areas of homes where they cannot work effectively. This is because moist air cannot effectively exit the dryer and exhaust to the outside—bogging down the entire drying process. If a dryer’s vent run is over 25 equivalent feet* or the dryer is experiencing long drying time, your dryer may need a dryer booster fan. The Dryer Duct Booster can also reduce the potential fire hazard associated with lint buildup.

* When using equivalent feet a 90° elbow equals 5 feet and a 45° elbow equals 2.5 feet. Some dryers can exhaust beyond 25 equivalent feet without a booster fan. - Tjernlund (2016)

And for commercial clothes dryer installations the company adds:

Individual vents can be expensive, if not impossible to install in multi-story buildings. Laundry room locations often force exhaust vent lengths to exceed the dryer manufacturers’ recommendations. Tjernlund systems allow exhaust vents to run hundreds of feet in any direction and vent diameter can be reduced by up to 50%.- Tjernlund (2016)

And Fantech offers similar advice for using a Fantech inline dryer exhaust fan:

According to some dryer installation instructions and local building codes, booster fans should be added in the dryer duct run when the length of duct exceeds 25 feet with no bends, 20 feet with one bend or 15 feet with 2 bends.

With an existing system you may find that drying times are far longer than the dryer manufacturers instructions give, this may indicate that you have an duct run longer and more restrictive than your dryer can handle. Installing a Fantech dryer booster in the duct line will relieve the excess pressure in the duct allowing the dryer to operate as designed. ...

The DBF 4XL, DBF 4XLT and RVF 4XL (with DB10 pressure switch) are effective for up to 130 equivalent feet of 4” hard duct. The DBF110 is effective up to 108 equivalent feet of 4” hard duct. At these lengths the booster fans will maintain a velocity 1200 feet per minute which will keep lint particles airborne guarding against build up in the duct.

... Over time the fan impeller may accumulate lint. Periodic inspection, based upon dryer usage, should be performed to ensure the fan impeller is not obstructed or loaded with lint. Under normal conditions, the fan should be inspected every six (6) months. Note: Excessive booster fan noise or vibration may be an indication of lint buildup on the impeller. ...

With the dryer operating, open the dryer door. The fan on the dryer will stop but you should still hear air being pulled through the dryer from the booster fan. Fantech's DBF 4XLT features a wall-mount indicator panel that mounts in the wall near the dryer. An LED light on the indicator panel lets the user know that the fan is operating correctly. - Fantech (2016)

Watch out: while it may be true that a booster fan can reduce lint accumulation in a long dryer run, as the notes above, should a dryer fire occur, or for that matter should other building fires occur nearby, the booster fan may actually speed the spread of a fire in the building.

Beers (2003) suggests an alternative: purchasing a clothes dryer designed with a stronger internal blower fan to handle longer exhaust duct runs. We've read references to "ventless" clothes dryers too, though one would wonder where the moisture is being sent and if it's wanted there.

Watch out: if a clothes dryer system is relying on a draft boosting fan for safe operation (say for a long dryer vent duct run or a run with many bends), be sure that the fan is operational. Otherwise the system is unsafe. That's because without the draft boosting fan the dryer system is at risk of overheating or a possible dryer fire. FanTech's DBF4XLT includes a light-indicator panel that shows if the fan is operating normally. Other brands and models with similar features may be available.

Clothes Dryer Exhaust Vent Draft Booster Fan Research

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