Thread: Dryer Booster Fan

Do booster fans "pulse" when the dryer is on, or is the fan intended to run continuously when the dryer is on. This one seamedf to be short cycling.

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Mathew, these fans should run continuously when the dryer is on. I could not see it in your photos but the more expensive fans operate by a pressure switch.


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Originally Posted by mathew stouffer

Do booster fans "pulse" when the dryer is on, or is the fan intended to run continuously when the dryer is on. This one seamedf to be short cycling.

Matt , when I was doing work in the PC area five years ago booster fans were flAt out not permitted there. The pulsing could because because the fan is starving for air

Ron, this is not in Park City Proper, and thank for the heads up I will look into that. So basically the fan is not designed to short cycle.

You could browse thru this website for info. I didn't see anything about blowing lint with that thing, but maybe. It's an Elicent inline fan, model 150A, made in Italy.

http://www.elicent.it/pages/Detail.aspx?ID=57

Hi Mattew, AS per what John said about lint and the fan you might also consider a lint trap before the fan and Yes i think it should be running continously while the dryer is running. the lint trap would also keep the pipe from filling up with lint but would also slow down the air flow from the dryer. so yes it would be a consideration as to if it was a good thing from a flow view. you would have to see what is right for that situation

As someone who has see these fans clog with lint, I found this interesting, I first heard about this fan from a local service that does a lot of duct cleaning and service in multi-unit buildings:


YouTube - Dryer Duct Booster Fan With LintBlitzer From Tjerlund

Hi Micheal, just watched the video on that fan. It works great according to the video how ever the lint is still a problem further down the pipes, I still think a lint trap is the best option to get rid of the lint from further clogging the pipes. Also it's strange too so much get's thru the first trap too. thanks for sharing the video it was a good one.

Unless my eyes are deceiving me, I cannot find anything allowing those dryer booster fans in clothes dryer exhausts.

SECTION M1502

CLOTHES DRYER EXHAUST
(This section is to long to post it all, but nothing in there allows those booster fans - could it just be that the lint problem keeps them from being allowed by the code? )

Lint is supposed to flow thru these fans. Most manufacturers recommend placing these fans at least 5 ' away from the dryer to allow the lint to dry so it doesn't stick to the fan itself. Lint traps should be placed on installs closer than that.

David,

This is not directed at you, but I would very surprised that lint would 'dry' in that short of an interval, especially at the rate the dryer exhaust expels air. Which, of course, always points back to fewer elbows, smooth wall venting, and the shortest possible runs. And we always find those installations

Jerry,
I'm not seeing anything in the code that says you can't use them either.

I have had a booster fan installed at my house for about 14 years. It does have a pressure switch that comes on a few seconds after the dryer starts, and runs a couple minutes after the dryer shuts off. It runs the entire time the dryer is on (to answer the OP question).

I disconnected the duct from my fan once in a while to clean the lint out, but found there was very little lint inside the fan. There very little build up in my ducts either.

The only thing that mine does once in a great while is NOT shut off after the dryer is finished with its cycle. I have to unplug it and plug it back in to reset it. It might do this once a year. FanTech mentioned this in the installation instructions.

Originally Posted by Jack Feldmann

I'm not seeing anything in the code that says you can't use them either.

Jack,

No, it do "not say" to not install a dyer booster fan, but then it does "not say" to not install a fireplace in there either.

If you follow that section and construct and install the duct as required, no booster fan is allowed (but then, neither is a fireplace either ).

Originally Posted by Jerry Peck

Jack,

No, it do "not say" to not install a dyer booster fan, but then it does "not say" to not install a fireplace in there either.

If you follow that section and construct and install the duct as required, no booster fan is allowed (but then, neither is a fireplace either ).

Booster fans were permitted up to the 2003 IRC, in 1501.3 Exception 1:

1. Where a clothes dryer booster fan is installed and listed and labeled for the application, the maximum length of the exhaust duct, including any transition duct, shall be permitted to be in accordance with the booster fan manufacturer's installation instructions. Where a clothes dryer booster fan is installed and not readily accessible from the room in which the dryer is located, a permanent identifying label shall be placed adjacent to where the exhaust duct enters the wall. The label shall bear the words "This dryer exhaust system is equipped with a remotely located booster fan."

Has been deleted from the 2006. But means it could have been legally installed.

Originally Posted by mathew stouffer

Do booster fans "pulse" when the dryer is on, or is the fan intended to run continuously when the dryer is on. This one seamedf to be short cycling.

OMG!!!!! Is that a six inch diameter exhaust being used for a dryer vent!!?? IMC says it should be only a four inch!! Or is the picture deceiving!!

Nope it's six inches.

Found nothing on elicents web site saying that fan was to be used as a dryer booster, thats why it has no pressure switch. That particular fan delivers 150 cfm and is used as an exhaust fan.

Originally Posted by Chris Roth

OMG!!!!! Is that a six inch diameter exhaust being used for a dryer vent!!?? IMC says it should be only a four inch!!

"IMC says it should be only a four inch!!"

The IMC says that? Where?

From IMC 504.6 (underlining and bold are mine)
- 504.6 Domestic clothes dryer ducts.Exhaust ducts for domestic clothes dryers shall be constructed of metal and shall have a smooth interior finish. The exhaust duct shall be a minimum nominal size of 4 inches (102 mm) in diameter. The entire exhaust system shall be supported and secured in place. The male end of the duct at overlapped duct joints shall extend in the direction of airflow. Clothes dryer transition ducts used to connect the appliance to the exhaust duct system shall be limited to single lengths not to exceed 8 feet (2438 mm)and shall be listed and labeled for the application. Transition ducts shall not be concealed within construction.

Originally Posted by Jerry Peck

"IMC says it should be only a four inch!!"

The IMC says that? Where?

From IMC 504.6 (underlining and bold are mine)
- 504.6 Domestic clothes dryer ducts.Exhaust ducts for domestic clothes dryers shall be constructed of metal and shall have a smooth interior finish. The exhaust duct shall be a minimum nominal size of 4 inches (102 mm) in diameter. The entire exhaust system shall be supported and secured in place. The male end of the duct at overlapped duct joints shall extend in the direction of airflow. Clothes dryer transition ducts used to connect the appliance to the exhaust duct system shall be limited to single lengths not to exceed 8 feet (2438 mm)and shall be listed and labeled for the application. Transition ducts shall not be concealed within construction.

Jerry. I have the same info from an OLD IMC Code. This may help. Here is the PDF on the NEW 2009 Codes.

Originally Posted by Chris Roth

Jerry. I have the same info from an OLD IMC Code. This may help. Here is the PDF on the NEW 2009 Codes.

If only 4" duct is allowed why does table 504.6.4.1 show reduction lengths for "dryer exhaust duct fittings" of 4", 6", 8", and 10"?

Originally Posted by chris mcintyre

If only 4" duct is allowed why does table 504.6.4.1 show reduction lengths for "dryer exhaust duct fittings" of 4", 6", 8", and 10"?

Yep I saw that one too. However the codes also say install according to manufacture's instructions which this information is also in the Operators Manuals when installing dryers. The reductions you speak of are for Commercial dryers as well were I service 6, 8, and 10 inch ducts. 4 inch are for household use. Good call Chris, good call.

Originally Posted by chris mcintyre

If only 4" duct is allowed why does table 504.6.4.1 show reduction lengths for "dryer exhaust duct fittings" of 4", 6", 8", and 10"?

Originally Posted by Chris Roth

Yep I saw that one too. However the codes also say install according to manufacture's instructions which this information is also in the Operators Manuals when installing dryers. The reductions you speak of are for Commercial dryers as well were I service 6, 8, and 10 inch ducts. 4 inch are for household use. Good call Chris, good call.

That is because that table is not address 4", 6", 8", and 10" diameter duct, it is addressing dryer duct with elbows of 4" radius, 6" radius, 8" radius, and 10" radius, and the larger the radius the less restriction there is on flow through the elbow and thus the shorter the "equivalent length" is.

Originally Posted by Chris Roth

Jerry. I have the same info from an OLD IMC Code. This may help. Here is the PDF on the NEW 2009 Codes.

Yes ... ... I used the OLD IMC as I have not installed the 2009 on my computer ...

The 2009 IMC DOES say: (underlining and bold are mine)
- 504.6.1 Material and size. Exhaust ducts shall have a smooth interior finish and shall be constructed of metal a minimum 0.016 inch (0.4 mm) thick. The exhaust duct size shall be 4 inches (102 mm) nominal in diameter.

I wonder why they are RESTRICTING the duct size to ONLY 4"? Could it be that some contractors installed 5" or 6" duct and connected a 4" outlet from a clothes dryer to it and the air flow was reduced such that the lint and air did not flow through the LARGER duct as fast or as far as if it had been a 4" duct? I can see why going to a larger duct would require a shorter duct run with the same size exhaust fan blowing into the exhaust duct.

Kinda like connecting a 1/2" garden hose and a 3/4" garden house together and connecting the 1/2" garden hose to the house bibb, then connecting the 3/4" garden hose to the end of the 1/2" garden hose and wondering why there is not as much pressure and the spray does not spray out as far (as compared to connecting the same garden hoses in the opposite order).

The code cites "a minimum" of 4 inches.
Domestic Dryers.

mf

Originally Posted by matt faust

The code cites "a minimum" of 4 inches.
Domestic Dryers.

mf

The 2006 IMC, yes, but NOT the 2009 IMC ... the 2009 IMC states that the size "shall be" ... and that is not a minimum ... it is a *specific* size of which *only* that size is allowed.

The 2009 IRC repeats the "shall be" which is found in the 2009 IMC:
- M1502.4.1 Material and size. Exhaust ducts shall have a smooth interior finish and shall be constructed of metal a minimum 0.016-inch (0.4 mm) thick. The exhaust duct size shall be 4 inches (102 mm) nominal in diameter.

Originally Posted by Jerry Peck

Yes ... ... I used the OLD IMC as I have not installed the 2009 on my computer ...

The 2009 IMC DOES say: (underlining and bold are mine)
- 504.6.1 Material and size. Exhaust ducts shall have a smooth interior finish and shall be constructed of metal a minimum 0.016 inch (0.4 mm) thick. The exhaust duct size shall be 4 inches (102 mm) nominal in diameter.

I wonder why they are RESTRICTING the duct size to ONLY 4"? Could it be that some contractors installed 5" or 6" duct and connected a 4" outlet from a clothes dryer to it and the air flow was reduced such that the lint and air did not flow through the LARGER duct as fast or as far as if it had been a 4" duct? I can see why going to a larger duct would require a shorter duct run with the same size exhaust fan blowing into the exhaust duct.Kinda like connecting a 1/2" garden hose and a 3/4" garden house together and connecting the 1/2" garden hose to the house bibb, then connecting the 3/4" garden hose to the end of the 1/2" garden hose and wondering why there is not as much pressure and the spray does not spray out as far (as compared to connecting the same garden hoses in the opposite order).

Jerry;

You hit the nail right on the head. Dryer exhausts that come out of the dryer are made 4 inches as well. When you increase the size to a larger size then you decrease the airs effectivness and ability to push the lint through the exhaust system. When I have taken my test in CDET (Certification for Dryer Exhaust Technictions) which is almost the same test for Chimney Sweeps I was amazed in how the 4 inch duct system was the only size that will effectivly push the right amount of air to push the lint out of the duct system. The minimum required air flow in MPH is 15 to effectively dry cloths. I have tested customers dryer ducts in MPH and in most cases after cleaning have increased the air flow by ab average of 19.4 to 22 MPH. Of course this is all based on the length which this includes all radious turns. Good call again

I believe the reason that the fan is pulsing is that something is wrong with the pressure switch. These switches operate on a differential of pressure. The fan will start when it senses pressure from the dryer, then the fan turns on, it reduces the pressure duct and the switch turns it off. I bet if you examine the system completely, you will find the pressure switch.

Run continuous. What may be happening is that there is lint debris lower in the duct (between the dryer and the booster fan) and the debris is "flapping" in the wind causing sporadic peak boosts of exhaust. The cycling is the end of the burst of a ploom of air as it belches out past the flap. The flap or debris falls back and creates back pressure until the exhaust once again has enough pressure to displace the debris obstruction for another belch of exhaust. The other condition may be that the fan is starting to fail and is "strobing". Another condition may be that there is "lint" at the axis where the fan blades meet the duct intake, jambs the blades temporarily until the electromotive force pushes past the "scuff point" for a large cycle of fan turns, then becomes jambed again until there is some force pushing the frame open again for a large number of fan blade cycles until it become obstructed again. Another possibility is checking out the Amperage consumption rating on the fan and seeing what other electrical devices are on the same breaker circuit; the circuit may be maxed out or using "nearly" all the amp rating of the breaker. Another "most likely" condition may be that there is a "goose neck" or dryer vent door that is hinged or slotted on the outside of the dwelling that is clogged with lint inside the door before it opens outside. The pressure of the boost fan is just enough to cause the door to open briefly allowing a ploom of exhaust, before the weight of the door causes it to fall back closed until the pressure builds up again allowing another ploom (belch) of exhaust. This is a common "regular maintenance" issue that is neglected. It is a common problem this time of the year when you have regular rain cycles making the vent doors wet and when small lint particles get past the fan they aggregate sticky and accumulate like snow drifts until you get the periodic cycling of the fan.

I have installed, and repaired many dryer ducts and boost fans in the past.

Originally Posted by Brian McGuinness

Run continuous. What may be happening is that there is lint debris lower in the duct (between the dryer and the booster fan) and the debris is "flapping" in the wind causing sporadic peak boosts of exhaust. The cycling is the end of the burst of a ploom of air as it belches out past the flap. The flap or debris falls back and creates back pressure until the exhaust once again has enough pressure to displace the debris obstruction for another belch of exhaust. The other condition may be that the fan is starting to fail and is "strobing". Another condition may be that there is "lint" at the axis where the fan blades meet the duct intake, jambs the blades temporarily until the electromotive force pushes past the "scuff point" for a large cycle of fan turns, then becomes jambed again until there is some force pushing the frame open again for a large number of fan blade cycles until it become obstructed again. Another possibility is checking out the Amperage consumption rating on the fan and seeing what other electrical devices are on the same breaker circuit; the circuit may be maxed out or using "nearly" all the amp rating of the breaker. Another "most likely" condition may be that there is a "goose neck" or dryer vent door that is hinged or slotted on the outside of the dwelling that is clogged with lint inside the door before it opens outside. The pressure of the boost fan is just enough to cause the door to open briefly allowing a ploom of exhaust, before the weight of the door causes it to fall back closed until the pressure builds up again allowing another ploom (belch) of exhaust. This is a common "regular maintenance" issue that is neglected. It is a common problem this time of the year when you have regular rain cycles making the vent doors wet and when small lint particles get past the fan they aggregate sticky and accumulate like snow drifts until you get the periodic cycling of the fan.

I have installed, and repaired many dryer ducts and boost fans in the past.

Brian;

My business is dryer ducts only. What is neglected is that the dryer vent must be 4 inch and not 6 inch. If the vent is changed then the proper air flow should keep the booster fan running continuely when the dryer is turned on. Check out the 2009 IMC and the 2009 IRC Codes. Also if I am not mistaken, I believe in the IRC it should also say that the booster fan must reside outside the direct flow of the dryer duct. NOT SURE HERE, ANY HELP OUT THERE!!??