Vent hood venting locations dilemma

12 years ago

Installing a 600cfm vent hood as part of a kitchen remodel. My dilemma is the location of the vent. I initially was thinking venting it straight up (about 8ft) to the roof via an 8in pipe, 1.5-3 ft feet above the roof line. My contractor is suggesting to go up into the attic make a 90deg turn then out the side of the house (about 33ft). The spec allows for a 35ft run.

The concerns are:
- another hole in the roof
- the side of the roof doesn't get much sun
- we are in New England, where we can have snow accumulation to cover the pipe (if not monitored)
- leaks
- loss of power and performance with a 33ft run and a 90deg angle in the exhaust pipe

Thanks in advance for your comments

Featured Answer

User

12 years ago

last modified: 12 years ago

Making the range hood code compliant will eliminate negative pressure and allow the hood to work more efficiently, even with a longer vent run.

http://publicecodes.cyberregs.com/icod/irc/2012/icod_irc_2012_15_sec003.htm

International Residential Code
M1503.4 Makeup air required.
Exhaust hood systems capable of exhausting in excess of 400 cubic feet per minute (0.19 m3/s) shall be provided with makeup air at a rate approximately equal to the exhaust air rate. Such makeup air systems shall be equipped with a means of closure and shall be automatically controlled to start and operate simultaneously with the exhaust system.

"ASHRAE's residential ventilation standard, ASHRAE 62.2, limits exhaust fans to a maximum of 15 cfm per 100 square feet of occupiable space, unless a backdrafting test is performed. According to this standard, the smallest home in which a 1,200-cfm range hood could be installed without verifying makeup air needs would be one measuring 8,000 square feet — a very large McMansion indeed."
http://www.greenbuildingadvisor.com/blogs/dept/musings/makeup-air-range-hoods

In your case, (600 cfm) your house would need to be 4000 square feet.

http://www.durangoherald.com/article/20140301/OPINION03/140309974/0/Opinion/Install-carbon-monoxide-detector-to-be-safe

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Comments (16)

PRO
Brickwood Builders, Inc.
12 years ago
If you have a clear shot straight up, I don't know why a turn would be suggested. What is his reasoning?

Remember that with a 600 cfm fan, make up air needs to be considered.
Manny O thanked Brickwood Builders, Inc.
Manny O
Original Author
12 years ago
a straight up shot is ok, however, the problem is the New England winters and snow accumulation not to mention vent would need to extend high above the roof line. The roof is over 20 years old (2 layers of shingles)
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Manny O
Original Author
12 years ago
the turn would be the 2nd option (instead of going straight up through the roof it would go out the side of the house.
PRO
Brickwood Builders, Inc.
12 years ago
Going straight out of the side of the house works great and would be my preference over taking it into the attic and then doing a 90 degree turn.
Futuro Futuro Kitchen Range Hoods
12 years ago
The power loss over a 90-degree turn is roughly equivalent to that of a 10- to 15-foot section of a straight duct. So, a 33' run + 90-degree turn = 43'-48' equivalent. Yes, it's over the manufacturer's recommendation, but if your outdoor environment dictates it, there's really no way around it.

That being said, keep in mind that the range hood manufacturer's recommendation for the length of the duct run is not a "hard line" - there is a *gradual* decrease in airflow, proportional to the length of the duct. We've had some clients who installed our hoods with duct runs ~50-60 feet, due to special circumstances. Even though it's less than optimal, it still works, at a reduced speed.

So, in your particular situation, it's not like the hood will work with a 35-foot duct, then drop dead at 36 feet. It will work, just won't be as powerful as it could be. Some loss of performance is good trade-off to avoid issues with snow, etc.
Manny O
Original Author
12 years ago
@Deborah going out the side will require @Futruro according to the manual the 90deg turn is approximately 5ft in length. @Fred, Yes we do have a makeup air system installed as per local code.
PRO
Brickwood Builders, Inc.
12 years ago
I think you know your answer then.
Futuro Futuro Kitchen Range Hoods
12 years ago
@salmonmaki: the manual's statement of a 90-deg elbow being equivalent to only 5 linear feet is very, *very* optimistic.

We prefer to err on the side of caution (with 15-ft equivalent), but, this being the Internet, and you should never believe a *single* source for anything ;) - here are some alternative sites that also show numbers in the 10-12-foot range:

Inspectapedia - http://inspectapedia.com/BestPractices/Kitchen_Vent_Fan_Specifications.htm

Emerson Swan -
http://emersonswan.blogspot.com/2013/02/static-pressure-bathroom-ventilation.html

Wood Magazine -
http://www.woodmagazine.com/woodworking-tips/techniques/dust-collection/figure-dust-collection-needs/?page=3
Manny O thanked Futuro Futuro Kitchen Range Hoods
Manny O
Original Author
12 years ago
that is excellent sources of information. Most refer to 4 and 6ft diameter ducts. The ones being installed are 8in diameter, this could be the reasoning for the 5ft. and the total was including the additional feet with the elbow, Thanks all for the insightful information. I am glad I found Houzz,
jcpc
12 years ago
What are the regulations for venting directly out the wall, when windows are nearby?
User
12 years ago
http://publicecodes.cyberregs.com/icod/irc/2012/icod_irc_2012_15_sec006.htm

http://publicecodes.cyberregs.com/icod/irc/2012/icod_irc_2012_3_par087.htm

http://publicecodes.cyberregs.com/icod/irc/2012/icod_irc_2012_15_sec003.htm

http://publicecodes.cyberregs.com/icod/irc/2012/icod_irc_2012_15_sec001.htm

http://publicecodes.cyberregs.com/icod/irc/2012/icod_irc_2012_3_par088.htm
jcpc
12 years ago
Thank you very much, very helpful!
mama2princess
10 years ago
Deborah Butler, funny you mention make up air... (I'm just searching IRC for other reasons:) My contractor didn't know about make up air, and Ferguson didn't mention anything about it when I bought our 660 cfm vent hood... We found out at the final inspection that we needed make up air and it cost an additional $1200! (Contractor claims he didn't know about it and Ferguson said "we don't know the codes of each city" (we're in the same city as Ferguson, so the city they're located in requires it... then they said "we don't know whether or not people are having their kitchens inspected"... those were the 2 reasons they gave for not mentioning it...
PRO
Brickwood Builders, Inc.
10 years ago
Ferguson (and all of the other appliance sales companies we deal with) will not bring it up to consumers. One would assume it is because they will lose the sale if they are the only ones that point it out. They don't see it as their responsibility to inform the public of the consequences of the purchase. Ferguson employees here locally know it is an issue - and they never bring it up. It's been in code for awhile - your contractor should have known if he/she does kitchens or new construction. Glad you got through it - but a surprise at the end is never pleasant.
Meesh
10 years ago
I must say that when we went to PC Richard to look at 48" ranges and accompanying hoods/blowers the salesman we talked to brought it up promptly. We had not been aware of it before. Kudos to PC Richard and Doug McGill- our sales guy in their Raritan, NJ store.

Vent hood venting locations dilemma

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Vent hood venting locations dilemma

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