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amakarevic 06-10-2008 05:14 PM

kitchen wall and bathroom fans sharing duct
 
i will have a recirculating microwave fan above the stove because i do not have ready access outside from where my kitchen is.

i was thinking of still fanning out of the kitchen but not directly from the microwave fan because the duct would be long and i did not want grease fumes to settle on the long way out (fire hazard). actually, in my jurisdiction, a stove fan must have immediate egress.

the way i was gonna accomplish that is that the recirculating fan was going to absorb most of the grease and recirculate degreased exhaust, which would then be going out the regular wall fan grid.

however, the only way to accomplish that is to share the bathroom fan duct.

to prevent the kitchen fumes going into the bathroom and vice versa, i was gonna use backflow stoppers that go inside the duct. i know these exist.

Q1: is this a realistic and safe agenda ?
Q2: i cannot remember the name of the company that makes these stoppers although i am positive i talked to their rep a few months back, without recording any notes. anybody know what i am talking about ?

thanks,

- a -

Termite 06-10-2008 05:19 PM

You need to install both items on their own ducts. They should not share a vent. Sharing a vent will make it a challenge for either fan to build any worthwhile static pressure and properly vent itself.

amakarevic 06-10-2008 05:59 PM

thanks. should i use regular circular 4 inch ducts for this ?

Termite 06-10-2008 10:31 PM

Flexible 4" works great for fart fans. Most hood vents must be in hard duct, but you have to check the manufacturers specs to determine the required size.

amakarevic 06-11-2008 12:56 AM

"fart fans" ... ROFLMAO !!!!!!!!!!!!!!!!

does that mean flex aluminum duct ? i would love to be able to use that instead of hard galvanized duct.

Termite 06-11-2008 01:13 AM

Hehehehe. I occasionally see "FF" designated on house plans, which stands for fart fan. 1 in 100 architects has a personality and a sense of humor.

Yes, they make a flexible foil vent that is listed for bath fans. Use foil HVAC heat tape to make the connection to the fan.

I used the stiffer expandable metal (not foil) vent duct for mine. It comes in a 3' section that extends to 8'. You can connect pieces end to end, and the price at the box store was competitive with the cheap foil stuff.

No need to use hard duct in a single family residence unless you somehow run through the garage wall or ceiling to access the outdoors. If you're in a townhome or condo that has firewalls or partywalls, you may need to hard pipe it to penetrate the rated fire assemblies.


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