Dryer Booster Fan

[charlie b]

. . . well since this was a spec house, and no dryer was present, the longest I could run the duct was 25', so I had to install a dryer booster. . . .

Did I just learn the answer to my earlier question (see post #2 in this thread). Is the purpose of a "dryer booster fan" to help push air through the exhaust duct to the outside world?

 

[mdshunk]

Did I just learn the answer to my earlier question (see post #2 in this thread). Is the purpose of a "dryer booster fan" to help push air through the exhaust duct to the outside world?

Yes, that's all it does. It's an inline fan that looks very much like most radon fans. It has a pressure switch built in to turn it on when it feels the flow of the air from the dryer.

The "25 foot rule" gets really tough when you consider that you need to subtract 5 feet for each 90. You have at least one at the bottom of the wall stack, and often one at the top. There's 10 feet knocked right off.

 

[yanici]

In my experience I've found that type of pressure switch to be finicky. Also, if it's sensing the positive pressure of the dryer blowing up the duct, won't the pressure start to go more negative when the booster fan starts up and sucks the air out?

 

[mdshunk]

In my experience I've found that type of pressure switch to be finicky.

What's the other type? That's the only type I know about.

 

[raider1]

I just did learn about it! didn't know the 25' foot rule. Which code local or IBC, IRC ETC....

Here in Utah, for a single family dwelling, it comes from the IRC.

Here is what the 2006 IRC says:

M1502.6 Duct length. The maximum length of a clothes dryer
exhaust duct shall not exceed 25 feet (7620 mm) from the dryer
location to the wall or roof termination. The maximum length
of the duct shall be reduced 2.5 feet (762 mm) for each
45-degree (0.8 rad) bend and 5 feet (1524 mm) for each
90-degree (1.6 rad) bend. The maximum length of the exhaust
duct does not include the transition duct.

There are a couple exceptions, but the one allowing a booster fan was eliminated, here is the exceptions:

Exceptions:
1. Where the make and model of the clothes dryer to be
installed is known and the manufacturer?s installation
instructions for the dryer are provided to the building
official, the maximum length of the exhaust duct,including any transition duct, shall be permitted to be
in accordance with the dryer manufacturer?s installation
instructions.
2. Where large-radius 45-degree (0.8 rad) and
90-degree (1.6 rad) bends are installed, determination
of the equivalent length of clothes dryer exhaust duct
for each bend by engineering calculation in accordance
with the ASHRAE Fundamentals Handbook
shall be permitted.

Chris

 

[yanici]

What's the other type? That's the only type I know about.

You're right Marc, they are all similar as far as I know too. You can, as you probably know, buy them with the switches having different degrees of sensitivity and some adjustable. Some have the capability of sensing on both sides of the fan output with two tubes, one on the high press. side and one on the low press. side. There you go. A lot of words with not much info.

 

[yanici]

Here's a link to a booster fan that uses a current sensing switch to energize the booster, instead of a pressure switch.

http://www.homeaire.com/product_details.aspx?l1=7&l2=2184&id=251

 

[kbsparky]

Did you read the instructions that come with that current sensing switch? Looks like you would have to mount that beastie in the panel box or use a separate enclosure with access to the dryer circuit wiring.

 

[yanici]

Did you read the instructions that come with that current sensing switch? Looks like you would have to mount that beastie in the panel box or use a separate enclosure with access to the dryer circuit wiring.

Whadda ya want, everthing easy?:grin:

 

[e57]

As an "Electrician" you would be hard pressed to find me touching duct work, picking location or anything else other than powering the fan fastened in place prior to my arrival....

Anyway, I too would see it as a laundry related piece of equipment and would (as I have many times without incident*) on the laundry circuit, hard wired or cord and plug.
210.52F "(F) Laundry Areas" Doesn't say what can or can not be on it - just that there be at least one receptical, and on a 20A circuit.

(*only on installs with electric dryer - where gas, with the possiblity of both washer and dryer used at same time, I use a different circuit. Even though the load of these things is really minimal.)


(edit:reapeating myself.... Bzzzzt.)

 

[benaround]

The current sensing device was pretty easy to wire, the c.s. uses the neut

to pull in a relay for the fan. Yes you need a 8x8x4 box for the c.s. and relay.

Q. On the type that sense the dryer fan come on to operate the booster,

when the dryer stops, how does the booster stop, it seems like it would

lock itself on by providing it's own flow of air.

 

[stickboy1375]

As an "Electrician" you would be hard pressed to find me touching duct work, picking location or anything else other than powering the fan fastened in place prior to my arrival....

This is a good point since you need a duct license in Connecticut, but i've never seen this enforced.... ??? Guess if they get some money out of it who really cares?

 

[Michael15956]

Anyway, I too would see it as a laundry related piece of equipment and would (as I have many times without incident*) on the laundry circuit, hard wired or cord and plug.
210.52F "(F) Laundry Areas" Doesn't say what can or can not be on it - just that there be at least one receptacle, and on a 20A circuit.

Only if the said fan is within 6 foot of the laundry receptacle, 210.50(C)

Michael

 

[stickboy1375]

Only if the said fan is within 6 foot of the laundry receptacle, 210.50(C)

Michael

Thats not what that says, all that says is the receptacle has to be within 6' of the intended location of the appliance, the laundry equipment is only an example... You can have as MANY receptacles as you want off the required laundry circuit 210.11(C)(2) as long as they are all installed in the Laundry area.... SO as long as the booster fan is LOCATED in the laundry area & has a cord, I don't see the problem...

 

[Michael15956]

Stickboy,

I just didn't make that up. Check out page 137 of the NEC Handbook, twenty-fifth edition. There is even a diagram there.

 

[e57]

Also nothing that says you can't install another receptical anywhere you like in the laundry area, or hard wire a booster fan on the roof on that circuit.

As you will be reminded (Often...), Handbook commentary is not actually part of the code, only an example...

 

[stickboy1375]

Also nothing that says you can't install another receptical anywhere you like in the laundry area, or hard wire a booster fan on the roof on that circuit.

As you will be reminded (Often...), Handbook commentary is not actually part of the code, only an example...

I don't see how you would meet code with that statement? Since when is the roof the laundry area? Unless of course your laundry is on the room.. :grin:

 

[Ragin Cajun]

FYI,

In this months issue of ICC's "Building Safety Journal" on page 58 is an add for a listed "Dryer-Ell" that has no 5 foot reduction.

www.dryer-ell.com


************


As to where to power the fan from, it doesn't look like a consensus has been found.



I guess to be "safe" I will power it from whatever is "handy."



Didn't mean to stir up the "nest."





Thanks,



RC

 

[raider1]

or hard wire a booster fan on the roof on that circuit.

e57,

You can't hard wire the booster fan on the laundry circuit. Check out 210.11(C)(2). This section states that the laundry circuit is to supply the receptacle outlets required by 210.52(F) and goes on to say that this circuit shall have no other outlets.

Chris

 

[Michael15956]

I know guys that the NEC Handbook is a guide and not a code requirement source.

But, it has been reported to be a creditable source for 25 editions, and at least I quoted a creditable source! Every time someone disagrees with the handbook, they say the same thing, "not a code requirement." I say no problem show me your source(s).

Michael