Venting Range Hood To Exterior Wall (from Interior Wall)


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Old 06-14-16, 04:53 PM
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Venting Range Hood To Exterior Wall (from Interior Wall)

Hi all,

I've posted about changing range from electric to gas and getting a new range hood on other posts, but this thread, I'm wondering the "best case" approach to getting a new range hood vented outside.

If you are standing in front of the range, the outside wall is 5' from center of the range to the left. Range hood will mount to the cabinets. The only way I can see doing this is to vent UP with the 7" round exist, elbow 90 to the left, and continue straight out the wall still above the kitchen cabinets.

My question is whether I should do this with 7" solid duct, or can I use 7" flexible pipe?

If I were to go through the cabinets, I'd lose a lot of cabinet space.. it's a small kitchen.

As far as the wall vent itself, I'm not finding a lot for 7" duct. Do I need to transition this 7" to a smaller size?

BTW, the range is 57,000 BTU, but I wouldn't ever use more than 2x burners at a time. I am looking at the Broan QP3 Evolution Series which is 450 CFM on high, but by spec it says it is only around 340 CFM on high if I use 7" round duct. Is this going to be OK?

Thanks!
 
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Old 06-14-16, 06:11 PM
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I would not consider using flex duct for a kitchen exhaust; it is not smooth inside and will trap grease and dirt.

Transitioning to a smaller size will further decrease the air flow. You might consider transitioning to a square or rectangular duct of equivalent cross sectional area or larger.

IIWM, I'd upsize the blower and be happy if I never had to go above medium. It will be a lot quieter, and it's nice to be able to turn it up to 11 if you are cooking something really smelly or smoky (on purpose or accidently ). How big is your hood and what is the volume of your kitchen? Those can figure into the calculation as well. As you probably know, the rule of thumb for sizing based on BTU is BTU/100. You may only use 2 burners, but it's not good practice to rely on self-imposed limitations.

If you have attic above, you might think about going up into that space to avoid having to deal with duct running across inside the kitchen. Then you could exit out a roof jack or sidewall.

Finally, you need to think about make-up air, especially if you have a fire place or gas appliances that do not have outside supplied air.

Good luck with your project!

[edit] One more thought...if you can get to attic space you could use a remote blower...much quieter.
 
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Old 06-14-16, 10:16 PM
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Thanks for the input.

The kitchen is approx 13'x12'x8', mostly open on one side, so approximately 1250 cubic feet... and if we're talking air volume, less since there's cabinets and a huge fridge.

This is the 1st floor of a 2 floor home, and there is no way I can get to the attic/roof without a major renovation. I also can't really go down easily, and as it is an interior wall, my options are further limited.

While I like the mentality to go with a larger CFM range hood, and never have to turn it to medium, I'm reading that if I go with larger than 400 CFM, I do need to provide makeup air.

The HVAC system was replaced in this home about 5 years ago by the previous homeowner. I am not sure if it is vented to outside for intake. There is a wood fireplace about 15 ft from the kitchen in the adjacent room, but it is never used.

The way I see it, my current range hood is just recirculating and probably isn't more than 200 CFM. I don't see the point in moving smoke from one place to the same room. So, I'd like it to go outside.

If I get around 325 CFM out of a range hood and it vents outside, what's the worst that can happen if something starts burning? The kitchen gets a little smokey? That happens now, so could it be worse?

And just like saying I might not use more than 2 burners at a time, if I go with a >500 CFM range hood and can't/don't provide make up air, then there's always just opening the kitchen window when the hood is on..

Back to duct work...

Why might I transition the 7" round to anything else? Just aesthetics?

As mentioned, I'm looking at Broan QP3, but would consider QP4 (though it's almost $100 more), which is 650 CFM. The QP4 says when using the 7" round duct, it is only 460 CFM on the highest setting. And if I understand correctly, I'll lose around 25 CFM for the 90 elbow. So, think I'll be OK without adding makeup air intake?

Thanks!
 
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Old 06-15-16, 01:02 AM
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While not as good in my opinion as a traditional range hood you might want to consider installing a down draft hood that would take away the smoke. Usually the venting for those goes in a basement and then out of the house via a vent but it could be used in a crawl space too just as well. If you are on a slab foundation then that wouldn't work and you may want to consider changing the floor plan of the kitchen.
 
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Old 06-15-16, 07:30 AM
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You're absolutely right, 350 CFM would be better than a recirculating hood.

If you have a gas furnace with outside supplied air, there will be two PVC pipes to the outside, one intake, one exhaust. If you only have one, it's exhaust.

I only suggested transitioning to square or rectangular because I though you said you were having trouble finding 7" round.....Also, it might be easier to box in or make less noticeable....

As far as need for makeup air, it's very dependent on how old the house is and type of construction. Given you said the HVAC was replaced 5 years ago, I'm guessing house is at least 15-20 years old, so it would not be built with tight sealing practices used today. You're probably OK even with the QP4.
 
 

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