range hood duct options

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Old 07-22-09, 05:14 PM
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range hood duct options

Greetings all. I am in the decision making process to install a range hood. I haven't purchased one yet, but have my eye on a Kenmore range hood that has two ducting possabilities. One is a 3 1/2"x11" rectangular out the back and the other is a 7" round out the top. The rectangular one out the back seems like it would be very fussy about tolerances since the duct would be extremely short and hole placement would be critical. The round outlet out the top and into the above cabinet and then out the wall seems a little easier to plan out where the hole is going to be in the wall. Another element is heat loss. Putting a gaping hole in the wall seems to defy all logic when it comes to keeping the heat in the house. Does anyone have any comments or experience they'd like to share?
 
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Old 07-22-09, 05:38 PM
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Sounds like the stove is on an outside wall. A direct vent through the wall would allow outside air leakage into the house through the hood, even with a damper (they are not that good).
I would go through the cabinets and the ceiling, then run horizontal through the attic and terminate at the soffit, with a damper. If the top of the hood will not accept a rectangular duct, ( many have knockouts for round or rectangular) start with a round to rectangular transition. Then run rectangular through the cabinets and into the attic. This will give more usable cabinet space. You can stay with the rectangular ducting in the attic or transition back to roiund if you wish.
 
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Old 07-23-09, 04:14 AM
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Hello, yes the stove is on an outside wall. The house is a two story so going through the roof is not an option as the stove is on the first floor. Hmmmm unless I run the rectangular duct throught the wall of the upstairs. I'd have to tear the wall apart upstairs. But then it could go up into the attic and out the soffit. Would that be worth all that work?
 
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Old 07-23-09, 02:16 PM
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Second floor makes it a pain. Have you considered a down draft exhaust? Of course a basement or crawl space is needed for that.

If you run the ducting up into the cabinets and then turn and go outside, with a damper at the range hood and a second damper on the outside deflector, you may reduce air leakage to a minimum.
 
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Old 07-23-09, 03:08 PM
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Hi bigguy, a seven inch exhaust implies to me a fairly large motor, so two comments.
1. When the fan is running and exhausting all of that nice warm air, an equal amount of not so nice cold air has to be coming in, somewhere. So dampers are just a part of the energy costs. As for dampers, I have seen somewhere, a pull chain version where you must open the damper for the hood to function. Just a thought.

2. When all that air is going out, you have to be sure your heating system is not starving for combustion air. This usually occurs in worst case conditions like dryer, bath fans, whole house fans, and the new beast all running at the same time, and in a fairly tight home. You can have it checked to be sure CO is not back drafting.

If you install anything in an outside wall, get as much insulation behind it as possible.

Best,
Bud
 
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Old 07-24-09, 05:24 PM
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So the guy at the appliance store said typically the vents are installed after the interior walls are finished and exterior siding is installed on a new construction. So here I am contemplating putting the vent outlet cap on first and then the interior drywall up after. I wonder which would work better. I am doing the entire renovation myself A-Z.
 
 

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