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ericadami 10-17-2010 03:03 PM

kitchen range exhaust design
Hi guys.

I am remodeling my kitchen and have a few questions about exhausting my slide in style gas stove.

I recently opened up the wall between my kitchen and living room and so wall mounts are not an option. I don't like the look of the "island style" range hoods which drop from the ceiling. What I want to do is build a cabinet/hood that will hang from the ceiling and fit an exhaust insert into the bottom. Something like this:

Its a one story house so I want to install an in-line blower in the attic or possibly an exterior blower on the roof.

I want the bottom of my hood cabinet to hang no lower than 42" above my stove for good visual clearance from kitchen into the living room. The above insert does have manufacturer recomendation of installing max 30" from stovetop but with a properly sized hood can I go higher? The stovetop is just above countertop level which is 36". My research indicates that steam and smoke expand outward at a rate of 3" for every 30" of vertical rise. My cooktop is 27"x 19" so I want to design my cabinet hood opening to be about 32" x 24". This is plenty of space for the rough opening for the insert linked above.

So my next question is how do I size my blower? Not sure exact BTU's of stove but its a fairly common 4 burner gas stove, I can look that up if it is helpful. I like the idea of a 600 CFM blower, but will that be adequate? Too much? My house is a 1949 build, roughly 1000 square feet with combined living area and kitchen making up about 500 square feet. It is not what I would call "tight", but the doors and windows are properly sealed up. Which leads to my next question, what about make-up air? I do not have a fireplace or chimney. I have a newer Bryant gas furnace in the crawlspace which has intake and exhaust which seems likely to be where the air would get drawn from if the windows and doors are closed when cooking in winter.

Also since my current ductwork runs from kitchen ceiling straight up to the roof I would like to use this duct (I believe it is 10"), BUT, it is about 5-6" off center from the new insert's vent position, as such would it be okay to jog the new vent several inches via a flexible piece of ducting inside the cabinet before attatching it to the current ductwork?

Thanks in advance for all suggestions.


hvac122 10-17-2010 07:47 PM

First, I would stay with the specs of the range hood as far as heights and clearances go. I guess you need to decide if you want the hood to work or would you rather see the other room?

Second a 600 CFM fan will have the ability to put your house in a negitive pressure when running. The air will have to come into the house somewhere. Do you have other gas units like a furnace or water heater? If so there could be potential to bring the flue gases back into the house. It is code here that you have to bring in fresh air somehow with anything over 300 CFM.

Third, the pipe you want to offset can not be done in flexable duct per code here. you would either need to cut the ceiling and see if its possible to move or move with a regid elbow or elbows.

ericadami 10-18-2010 12:40 PM

Thanks for your response.

I do agree about following manufacturer specs, and I want the exhaust to work, but I really want to install one that can be hung higher than the standard 30". I'll need to research this further.

I have 3 gas appliances including the Bryant furnace, a Rinnai tankless water heater and the stove. I certainly don't want to create negative pressure. I have been reading about makeup air ductwork with electrically controlled damper that opens whenever the fan comes on. That seems pretty straightforward. Sizing of this ductwork would seem important and I do wonder what is customary in terms of vent placement. I was thinking, if I go this route, of placing the make up air vent directly in the floor under the stove and running it through the crawlspace to the exterior.

As far as using the original ductwork I can design my cabinet so that the original 10" hole in the plaster in the kitchen ceiling would be covered and cut a new hole where I need it. Then use elbows to tie it in to the original ductwork in the attic. In this case I would lean toward the inline fan since I would be making adjustments to the original ducting anyhow.

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