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Boosting a Dryer Vent

jar546

jar546

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Oct 16, 2009
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Yes, this was installed on a dryer vent that was about 36' from the dryer connection to the exterior. This was used as a booster. Thoughts? Code Compliance? You can ignore the non-compliant, upside-down, exposed, paper-faced insulation. That is a topic for another discussion.

IMG_9906.JPG
 
It's hard to tell what kind of fan that is. It looks more like a radon exhaust fan than anything else but it could be in HVAC duct booster fan. Either way it's not designed for this purpose. I'd be very interested to know how they are turning it on (manually or automatically) but in either case I'm sure it's not intended for that kind of use. As far as code compliance goes I'm not really sure.
 
No where in the code 2012 editions does it address booster fans for residential dryer systems. It is a maximum 35 ft length or what the manufacture of the dryer specifies.

IMC 2012
504.6.4.2 Manufacturer’s instructions.
The maximum length of the exhaust duct shall be determined by the dryer manufacturer’s installation instructions. The code official shall be provided with a copy of the installation instructions for the make and model of the dryer. Where the exhaust duct is to be concealed, the installation instructions shall be provided to the code official prior to the concealment inspection. In the absence of fitting equivalent length calculations from the clothes dryer manufacturer, Table 504.6.4.1 shall be used.


I see the 2018 does allow booster fans. We should have those adopted about January

M1502.4.4 Dryer exhaust duct power ventilators.
Domestic dryer exhaust duct power ventilators shall conform to UL 705 for use in dryer exhaust duct systems. The dryer exhaust duct power ventilator shall be installed in accordance with the manufacturer’s instructions.
 
Last time I checked, there were no listed booster fans...….the motors are the problem, so I have been told.
 
How about the unlisted duct tape as well? If it is listed, the foil side will be marked(labeled).

M1601.4.1 Joints, Seams and Connections (paraphrased)
Longitudinal and transverse joints, seams and connections in metallic and nonmetallic ducts shall be constructed as specified in SMACNA HVAC Duct Construction Standards‒Metal and Flexible and NAIMA Fibrous Glass Duct Construction Standards. Joints, longitudinal and transverse seams, and connections in ductwork shall be securely fastened and sealed with welds, gaskets, mastics (adhesives), mastic-plus-embedded-fabric systems, liquid sealants or tapes. Tapes and mastics used to seal fibrous glass ductwork shall be listed and labeled in accordance with UL 181A and shall be marked "181A-P" for pressure-sensitive tape, "181 A-M" for mastic or "181 A-H" for heat-sensitive tape.​
 
mark handler said:
this one is listed with Inertek, another ICC approved testing company
https://hw.menardc.com/main/items/media/BODOR001/Prod_Tech_Spec/DryerBoosterVKPSSpecSheet.pdf
Click to expand...

Mark, unfortunately, this one is not listed as a Dryer Exhaust Duct Power Ventilator (DEDPV) under ETL or UL. For this product to be listed, it must be under the category of DEDPV. This fan's key give-away is the use of the term "booster fan" in it's literature instead of DEDPV. A listed DEDPV would not call their product a "booster fan."

ETL has one listed DEDPV, Model LB2 - https://ramuk.intertekconnect.com/W...e7894f997d386a08862581360051d85a?OpenDocument

The booster fan in Mark's post has just about everything except DEDPV - https://ramuk.intertekconnect.com/W...6860ea9a49216e61862583f900661559?OpenDocument

UL has only two listed DEDPV, models DBF4XLT-705 and DEDPV-705 (see Ty J posted link). This should not be confused with model DBF4XL-705 which does not have the DEDPV listing.
 
Nobody likes to make it easy on the code officials. If you follow the link to the UL listed DEDPV (DBF4XLT-705 and DEDPV-705), you will find that these are manufactured by Systemair, or Fantech. If you go to the second link that Mark provided in post #4, you will find this statement on Fantech's website:

What is the maximum length of duct that can be used with a Fantech dryer exhaust fan?
The DEDPV-705, DBF 4XL, DBF 4XLT and RVF 4XL (with DB10 pressure switch) are effective for up to 130 equivalent feet of 4” hard duct. The DBF 110 is effective up to 108 equivalent feet of 4” hard duct. At these lengths the booster fans will maintain a velocity 1,200 feet per minute which will keep lint particles airborne guarding against build up in the duct.

Notice the use of the term "booster fans" ! This is implying that five of these models are DEDPV listed. They are not, only two are. I have had to point this out to designers and contractors on several occasions when they had been manipulated into thinking they have a listed product. When asked for them to produce the listing of the other three from the manufacturer, I received nothing.
 
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The whole key is what standard is the fan listed to? All exhaust fans are listed, but in order to be used for dryer exhaust they have to be listed to UL 705 for use in dryer exhaust. Of the ones rgrace named, four are only listed to UL 507, the listing for standard exhaust fans of most types, not for dryers. Even the model numbers give away which one is actually the dryer fan. DEDPV-705: Dryer Exhaust Duct Power Ventilator UL 705 listed.
The other key is they need to be installed pre manufacturers instructions. Note that this one has a remote indicator to be located by the dryer to indicate trouble, it comes with quick disconnect duct drawbands to allow for service and cleaning removal, and the instructions are pretty specific where the fan can be located in relation to the dryer and termination. I've never seen a 705 listed dryer fan with a plastic housing. Probably way to much potential for static electricity problems with dryer lint brushing past the plastic.
 
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