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  • Feb 23rd, 2021 12:20 am
Deal Addict
Feb 26, 2016
1382 posts

Make up Air System

I've purchased a new build and the builder won't let me increase the duct size from 6" to 8" because of negative air pressure. I decided that I'll probably do it after closing anyway because I'd like to have a range hood that is at least 700CFM and most range hoods with 700CFM+ require 8" ducting. Although the rangehood will have to ability to go up to 700 or 1000 CFM, it's highly unlikely that I'll run it at the maximum very frequently or for extended periods of time. I just want the option to be able to run it at the maximum for the odd time we're grilling a steak or something that might stink up the house. Has anyone ever experienced negative air pressure and/or installed a make up air system? I'm assuming most people have not but I wanted to confirm if this is something I need to consider if I were to go with a higher CFM range hood.

Here's a good article of negative air pressure and why installing a make up air system can improve air quality in the house.

https://www.pvhvac.com/blog/before-you- ... -read-this

On a separate note, we all know that we should probably open our windows once in a while to let "fresh air" into the house even during the Winter. Curious how frequently you guys do this and wondering how much this actually helps reduce negative air pressure.
3 replies
Deal Addict
Sep 13, 2016
3322 posts
Wont be able to comment on the negative pressure thing, but we do try to open windows for a few minutes every other week as long as it is not freaking cold. Also when doing so, I try to open windows on the opposite ends of house together so that it can make a nice channel.
Apr 19, 2018
348 posts
You won't need make-up air unless you are running a fan with serious cfm like over 1000. I have a ventahood thats rated at 900 cfm and dont have any issues. The best way to get good air into your home is opening a window. Don't waste your hard earned money on a makeup system. Get a ventahood pro liner for your kitchen you wont regret it
Don't worry be happy - Bob
Mar 17, 2004
492 posts
I had the HVAC guy change out the standard 6" duct to 8" during construction. Don't regret it at all. Hood fan is quiet enough @ max to carry a normal volume conversation, any lingering odors from cooking are gone within minutes after cooking is done. We've got an HRV running 24/7, so don't often open windows during winter months. The odd time that I do crack the windows open with the hood fan on max, there's definitely a noticeable draw of outside air. Same as when I crack open an outside door, it gets sucked open, so there's definitely a negative pressure present


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