#32
So I casually mentioned to the building inspector for my kitchen remodel that I planned to install a vent hood over the island range. He mentioned if I go over 400cfm I have to introduce return air equal to the exhaust rate.  the conversation ended there (for now)

ugg.  Haven't picked a vent hood yet, but I'm honestly not sure I need to go over 400cfm..   It's a 5 burner gas range with a total of 48,000 BTU if everything were cranking (which would be rare for us)..   The rough rule of "100CFM for every 10k BTU" would put me at 480cfm, but if I went with a 390CFM model (which do exist) then I wouldn't have the makeup air requirement. 

Thoughts? Would the added cost of finding a way to add return air be worth it or is a vent hood more than 400cfm really not necessary?
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#33
It’s not return air, it’s makeup air. In a residential scenario it can be a giant PITA to install and balance without significant effort. Placement and additional heating or cooling load can be nightmarish. I strongly recommend staying around the 300 cam exhaust.
Blackhat

Bad experiences come from poor decisions. So do good stories. 


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#34
(10-12-2022, 09:30 AM)blackhat Wrote: It’s not return air, it’s makeup air. In a residential scenario it can be a giant PITA to install and balance without significant effort. Placement and additional heating or cooling load can be nightmarish. I strongly recommend staying around the 300 cam exhaust.

understood return vs. makeup, mispoke.

Yah, brainstorming options here.   As long as a < 400CFM fan is suitable for my modest needs that's probably a way to go.

This is residential, but the walls are all open where the remodel is happening so it could probably be done a bit easier. 

My HVAC buddy said "why not install an ERV" - which has added benefits, something to think about...
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#35
Are you suggesting an ERV to replace the exhaust fan?  I would be cautious that it’s filters, fans and cores are rated for that use. The biggest issue with makeup air, particularly untempered air is where to discharge it into the building without creating a cold draft or excessively cooling a space.   Even an ERV will not raise outside air temps more than roughly 10F. Going the other way, on a hot day is far less objectionable.
Blackhat

Bad experiences come from poor decisions. So do good stories. 


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#36
(10-12-2022, 11:30 AM)blackhat Wrote: Are you suggesting an ERV to replace the exhaust fan?  I would be cautious that it’s filters, fans and cores are rated for that use. The biggest issue with makeup air, particularly untempered air is where to discharge it into the building without creating a cold draft or excessively cooling a space.   Even an ERV will not raise outside air temps more than roughly 10F. Going the other way, on a hot day is far less objectionable.

No, not to replace the fan..  To bring fresh air into the house (and I suppose bring the other benefits of an ERV like the filtration and energy cost reduction)

I admit I'm a bit unclear how that would work, but my HVAC buddy first made the suggestion, and then this morning the building inspector also told me that if I installed an ERV somewhere in the house that would meet the requirements if my hood is 400+ CFM (or, he said, just stay below 400)
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#37
I can't help in regards to the return air, but I do have a 5 burner gas stove top that is 30" wide. There is no way you can use all five of those burners in a 30" space. Maybe if it was a 36". But with ours I think the most I've had going at once is 3, maybe 4 (with probably 2 on simmer).

That said our vent hood is 600CFM, and I love it. First one I've ever had that can actually move enough air to make a difference (granted, every prior place was a rental with crap vent hoods or the dreaded microwave/vent combo). It has four speeds. I primarily use the lowest two. But if I'm using high heat while searing or using a wok those two higher speeds are nice (but loud).

Then again I like to cook. Probably also depends on how much of that your family does.

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#38
(10-12-2022, 05:39 PM)msweig Wrote: I can't help in regards to the return air, but I do have a 5 burner gas stove top that is 30" wide. There is no way you can use all five of those burners in a 30" space. Maybe if it was a 36".  But with ours I think the most I've had going at once is 3, maybe 4 (with probably 2 on simmer).

That said our vent hood is 600CFM, and I love it. First one I've ever had that can actually move enough air to make a difference (granted, every prior place was a rental with crap vent hoods or the dreaded microwave/vent combo).  It has four speeds.  I primarily use the lowest two. But if I'm using high heat while searing or using a wok those two higher speeds are nice (but loud).

Then again I like to cook. Probably also depends on how much of that your family does.

I was in a small doing an inspection. Usually I walk into a kitchen and turn on the exhaust fan and light first. I got sidetracked and left the room and went in into the basement I was there a while explaining the water treatment system to the client. When I went back up, her husband said the bathroom exhaust fan came on by itself.. The makeup air was coming though the bathroom exhaust fan making the blade spin. It took a while to figure it out.
Neil Summers Home Inspections




I came to a stop sign and a skanky tweaker chick in a tube top climbed out of the brush and propositioned me.  She looked like she didn't have any teeth so I counted that as a plus.


... Kizar Sosay





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#39
(10-12-2022, 09:07 PM)Snipe Hunter Wrote: I was in a small doing an inspection. Usually I walk into a kitchen and turn on the exhaust fan and light first. I got sidetracked and left the room and went in into the basement I was there a while explaining the water treatment system to the client. When I went back up, her husband said the bathroom exhaust fan came on by itself.. The makeup air was coming though the bathroom exhaust fan making the blade spin. It took a while to figure it out.

That could make dinner smell.....interesting.
Sign at N.E. Vocational School Cabinetmaking Shop 1976, "Free knowledge given daily... Bring your own container"
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#40
(10-12-2022, 09:38 PM)MstrCarpenter Wrote: That could make dinner smell.....interesting.

lol. 
doesn't that also mean the bathroom fan lacks a damper? Shouldn't that only be able to push, not pull air?
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#41
Seems there may be a lack of understanding on the function and capacity of ERVs. An average residential ERV will have a net positive flow of 40 or 50 cfm. That doesn’t mean much when a range hood kicks on and rips 400 cfm out of the house.
Blackhat

Bad experiences come from poor decisions. So do good stories. 


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gas ranges, vent hood and.. return air


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