Can anyone please give tell me what the difference between a DEDPV and a booster fan is? I cannot seem to find anything that says how they differ. I believe they each will let the exhaust duct go past 35'. Other than that, I can't see any difference, only that domestic booster fans shall not be used in dryer exhaust systems (i don't know why not).
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DEDPV vs booster fan
- Thread starter yvette
- Start date
klarenbeek
Silver Member
DEDPV stands for Dryer Exhaust Duct Power ventilator. It listed to UL 705 specifically for use in dryer exhaust duct systems. The ones I've seen have metal housings, not plastic, and some sort of indicator or alarm telling you if the fan is not working or plugged. The instructions may also give specifics about where it can be placed in the system.
The old booster fans don't have the alarms and the ones I saw were always plastic. They are actually just in line exhaust fans, ok to use for things like bathroom exhaust, but never actually approved for dryer exhaust. The issue with dryer exhaust is you are moving lint as well as air. There's issues with moisture, and static electricity on plastic, that can create excessive lint buildup, and the fact that lint is a high fire hazard. They typically don't have anything to tell the owner when they stop working either other that the dryer all of a sudden not working worth a crap.
The old booster fans don't have the alarms and the ones I saw were always plastic. They are actually just in line exhaust fans, ok to use for things like bathroom exhaust, but never actually approved for dryer exhaust. The issue with dryer exhaust is you are moving lint as well as air. There's issues with moisture, and static electricity on plastic, that can create excessive lint buildup, and the fact that lint is a high fire hazard. They typically don't have anything to tell the owner when they stop working either other that the dryer all of a sudden not working worth a crap.
Klarenbeek has nailed the answer perfectly!
If you are dealing with a dryer duct, you must use a DEDPV.
As for why this is the case, see the following code sections:
If you are dealing with a dryer duct, you must use a DEDPV.
As for why this is the case, see the following code sections:
2021 IRC
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.M1502.4.5 Booster Fans Prohibited
Domestic booster fans shall not be installed in dryer exhaust systems.
Paul Sweet
Sawhorse
I understand that this is a change in the 2021 code.
I believe that 2021 IRC Section M1502.4.5 is new, but M1502.4.4 is not. That said, I don't believe that booster fans were ever truly permissible. Their listings were not inclusive of dryer exhaust duct systems. Not saying that folks were aware of that, but I do not believe that the 2021 code is a substantial change. DEDPV were already the correct piece of equipment, the 2021 just spelled it out further because of folks not reading the listings.
2018 IRC
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.
ICE
Oh Well
California Mechanical Code
504.4.2.1 Length Limitation. Unless otherwise permitted or required by the dryer manufacturer’s instructions and approved by the Authority Having Jurisdiction, domestic dryer moisture exhaust ducts shall not exceed a total combined horizontal and vertical length of 14 feet, including two 90 degree elbows. A length of 2 feet shall be deducted for each 90 degree elbow in excess of two.
Exception: Where an exhaust duct power ventilator, in accordance with Section 504.4.2.3, is used,the maximum length of the dryer exhaust duct shall be permitted to be in accordance with the dryer exhaust duct power ventilator manufacturer’s installation instructions.
504.4.2.3 Exhaust Duct Power Ventilators
Dryer exhaust duct power ventilators for single residential clothes dryers shall be listed and labeled in accordance with UL 705 and installed in accordance with the manufacturer’s installation instructions.
Quite often I encounter a duct that exceeds the length limitation but the installer increased the diameter of the duct to compensate.
504.4.2.1 Length Limitation. Unless otherwise permitted or required by the dryer manufacturer’s instructions and approved by the Authority Having Jurisdiction, domestic dryer moisture exhaust ducts shall not exceed a total combined horizontal and vertical length of 14 feet, including two 90 degree elbows. A length of 2 feet shall be deducted for each 90 degree elbow in excess of two.
Exception: Where an exhaust duct power ventilator, in accordance with Section 504.4.2.3, is used,the maximum length of the dryer exhaust duct shall be permitted to be in accordance with the dryer exhaust duct power ventilator manufacturer’s installation instructions.
504.4.2.3 Exhaust Duct Power Ventilators
Dryer exhaust duct power ventilators for single residential clothes dryers shall be listed and labeled in accordance with UL 705 and installed in accordance with the manufacturer’s installation instructions.
Quite often I encounter a duct that exceeds the length limitation but the installer increased the diameter of the duct to compensate.
steveray
SAWHORSE
klarenbeek
Silver Member
That actually makes the problem worse. The airflow will lose static and velocity causing more lint to drop out of the airstream. Not sure what flies in California, but the IMC specifically requires the duct size to be 4" round. Even going oval or rectangle with the same volume will cause some of the same issues.
ICE
Oh Well
504.4.2 Domestic Clothes Dryers. Where a compartment or space for a Type 1 clothes dryer is provided, not less than a 4 inch diameter exhaust duct of approved material shall be installed in accordance with Section 504.0.
Type 1 clothes dryer exhaust ducts shall be of rigid metal and shall have smooth interior surfaces. The diameter shall be not less than 4 inches nominal, and the thickness shall be not less than 0.016 of an inch.
They are convinced that going from 4" to 6" is a 50% increase and more is better.
Last edited:
2021 IRC M1502.4.1 Material and Size
Exhaust ducts shall have a smooth interior finish and shall be constructed of metal not less than 0.0157 inch (0.3950 mm) in thickness (No. 28 gage). The duct shall be 4 inches (102 mm) nominal in diameter.
ICE
Oh Well
Does the IMC state that the duct shall be round? The UMC states 4" diameter. One could take diameter to mean round.
ICE
Oh Well
California didn't adopt the MEP provisions in the IRC. It is a duplication of effort. I have not found the reason behind that.
Was not responding to you ICE... just put the IRC section out there for those of us not in CA.
For those of us not in CA, it really isn't a duplication of effort. It is actually simpler in that for residential builds, you only need the one book (IRC). You don't need the MEP books because everything is in the IRC.
ICE
Oh Well
Well I didn't think that you were.
It's not my fault that you're not in California.
Oh but it is. You had to learn it. It's a whole lot more pages in the book when all of those pages are already in a book.
Oh and how's that? Is it a less stringent code? Fewer sections? Watered down?
Alarighty then... so why have two books? I am pretty sure that every time there is any contention you are walking back and forth between the IRC and MEP code books. I know that I would and there's no difference between me and the rest of the inspectors out there.
ICE
Oh Well
Oh just relax... you'll need to go a lot further than that to offend me. If I want to argue I'll ring up fatboy.
steveray
SAWHORSE
Unless you are stupid like CT and you delete the electrical and make them use the NEC...
WA actually deletes the electrical (in favor of the NEC) and the plumbing (in favor of the UPC), so I get it.