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help with hvac issues regarding kitchen hood, inline fan and cfms

12 years ago

We are installing a gas range with a total BTU output of 85,000 into a new construction home. The home is nearly completer and all the duct work is in place. The recommendation for the CFM's for the hood is about 1200. Unfortunately, our builder made some major errors in his construction of the ventilation for the hood, and there is only a 7" diameter round duct for the hood to connect to. The HVAC folks say the pipe can only accomodate a 600 CFM fan. There is no way to get a bigger diameter duct in the wall without creating a horrible, unsightly "bump out" into the main first floor hall of the house (this is not an option). So we are left with a range needing a 1200 CFM fan, but our builder only saying the duct can accomodate 600 CFM. He and the HVAC guys are suggesting we put a regulare 600 CFM fan in the hood itself, and then also a "booster" inline fan in the duct work (we have a long run of duct work that runs from the fan, takes a 90 degree turn, and runs under the kitchen and out the house...yes, another poor design.) Does anyone have any experience in this area as to whether this logistically makes sense or if it will really make up for the addtional CFM's needed? He wants to charge us an additional $2,000 for the inline fan and install, so I don't want to do it if it isn't going to help move the air. Thanks

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