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CFM of Dryer exhaust?

dovetail97128's picture

I am curious about the CFM of an electric clothes dryer exhaust. Recently remodeled and have a very tight laundry room, wanting to add exterior drawn "make up air" to the room so the dryer doesn't draw heated air from the rest of the house and cause drafting .
What I am really looking for I guess is some information on what size opening would be needed to provide the "make up air".

Edited 12/10/2006 1:11 pm ET by dovetail97128

Life is Good

(post #113692, reply #1 of 11)


The airflow of dryer vents varies, but is generally in the range of 100 cfm to 225 cfm.

(post #113692, reply #4 of 11)

Thanks , with that information I will be able to talk to friend who is in HVAC and have him size me a inlet pipe with a backdraft damper that will draw air from the attic space.
Room has no window so that option is out
(Backdraft damper will be a simple counterweighted damper)

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(post #113692, reply #2 of 11)

This is a tough nut to crack. Many have tried to devise a practical and cost effective version of this. One problem is that the damper needs to be motorised in order to avoid having air that is able to enter freely in one location and exit freely in another.

Controllling this would have to be manual or automatic. In the case of a manual system, a window is adequate if it is well separated from the exhaust and is easier to remember to close than a ducted design. In the case of automatic, you would have a sensor that tracked run time of the dryer had a relay to control the damper and possibly a fan. Placing the dryer outside the building envelope is a good solution if it is well thought out.

Please let us know what you come up with as this is one of those nagging little problems that is yet to be solved to my satisfaction.

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There is only one planet earth. How many chances do you think we get with her?

(post #113692, reply #3 of 11)

Why not a one of the flap dampners.

I think tht the name is Chutes or something like that that is designed for automatically reducing back drafting.

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(post #113692, reply #5 of 11)

Homes have many dampers that allow air out but not in. They inclue bath vents, exhaust hood vents and dryer vents. If you add one that lets air in but not out, you now have a pathway in and out of the house anytime the wind blows or anytime there are mechanically driven differences in the pressure boundary. (negative pressures caused by a leaking HVAC system) Vents for allowing the entry of air into a building have to have motorized and sealed dampers to prevent this.

There is only one planet earth. How many chances do you think we get with her?

There is only one planet earth. How many chances do you think we get with her?

(post #113692, reply #6 of 11)

Barometric dampers are a better solution than a simple flap.

Skuttle "valves" aka "Self-Adjusting Make-Up Air Control" used to provide fresh air to forced air returns are a form of barometric damper, I believe

I don't know what the sensitivity on the Skuttles is, they work off the return air flow/pressures and might not be as sensitive as a standard barometric damper: see, e.g.,

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(post #113692, reply #7 of 11)

Time to elaborate on the situation.
The Laundry is a room between the shop/garage and the house.
Two doors, one into each adjoining space, no windows, contains no devices needing outside combustion air. Nor does it have any outside heat source or vent connection to the main house
I don't want to suck dust from the shop into the laundry room so it has a weather stripped and sealed door.
Nor do I want to pull conditioned air from the main house.
Therefore I was looking for an exterior air inlet (which is limited to either crawl space or attic because the laundry room has no exterior walls) I decided against the crawl space because I saw no sense in creating unneeded drafts under the heated house all winter. So all I am looking at is a simple damper that will open when the dryer is running, close when it is not.
I don't really care if it drafts a bit when the dryer is off, but do worry about straining the dryer trying to pull against a vacuum in a tightly sealed room, or pulling air from the adjoining spaces..
Thanks to all for the input on solutions.

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(post #113692, reply #8 of 11)

Oh! Why didncha say so? In that case, check out the products from Seiho. Also anybody else that wants the slickest little stainless steel, spring return, easy to clean dryer vent that they ever laid eyes on. It's the cat's meow.

There is only one planet earth. How many chances do you think we get with her?
There is only one planet earth. How many chances do you think we get with her?

(post #113692, reply #9 of 11)

Good thread. It seems like dryers could have makeup air available via a concentric vent pipe, but in the winter you'd have to heat that air to make it dry clothes, and how would that be any better than just heating the air with your heating system and drawing it out of the house?

(post #113692, reply #10 of 11)

David, Hmm , now you have me thinking .. energy expanded to heat the air will remain the same no matter what the source of the air. I was only thinking along the lines of drafts, well and I know I want to exclude the shop dust!
I guess I could cut a small vent into the house /laundry door and be done with it instead of ducting and dampering.
As it is the laundry is "self " heating off the electric water heater.
I am balancing having to pay for the heat loss from the heater against having a happy GF who hates cold laundry rooms, so I haven't insulated the tank yet. Figure I pay for heat at the same rate whether it is loss off the water heater or space heat .
Need to broaden my focus from "tight house building techniques" to include the actual scenario.

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Fresh Air Intake Vent in dryer room (post #113692, reply #11 of 11)

Hi, if you've found this older page on dryer make up air concerns, please watch my youtube video about the make up air vent we installed at our house.


I imagine there are a lot of people with homes that have the laundry room configuration that makes having a make up vent very helpful!


Those things are:

Strong dryer, long exhaust run.

Laundry room with no windows, located in middle of house.

Tight house overall, especially for families that don't like opening windows.


Watch this video, you'll be surprised