I'm planning to install a 20-foot duct in my townhome that goes straight up through the roof, which we've already got approved by the HOA. Currently, we're trying to avoid make-up air since that creates more complications with the HOA, though we might consider that later. The only alternative we have is a recirculating hood.
We have a 36" induction cooktop and are thinking about using a 300 CFM Vent-A-Hood liner (BH134PSLD). My main concern is whether 20 feet is too long for the venting system. What potential issues should I be prepared for? For instance, could this length lead to condensation, cause odors to linger in the duct and seep back into the house, or are there other challenges I should know about?
5 Answers
Most codes allow a maximum of 35 feet for duct runs. Any bends or elbows will add about 3-5 feet each. And while a 300 CFM hood isn’t the strongest, you can go up to 400 CFM without needing make-up air.
Generally, you don’t need make-up air for exhaust systems under 400 CFM. Most older homes are drafty enough that you might be able to push your limits a bit without issues. But just keep in mind that it sounds like you guys have to stick to code for your inspections.
We actually need it inspected before moving back in. If we were swapping out an old model for another, the 600 CFM would be simpler, but for now, we need to play by the rules.
20 ft should be fine as long as you’re not dealing with any turns. Make sure you’re using the right size duct and fittings. It’s a good idea to use thicker ducting and secure it well; thin ducting can get noisy in windy conditions. Here's a great article I found on the subject! [Kitchen Duct Guide](https://kitchen.services/range-hood-duct-complete-guide/)
Thanks for the article! Should I insulate the ducting, or is that a code issue? I was thinking about wrapping it in foil at least in the attic to prevent condensation. Are there any drawbacks to that?
According to the manufacturer's instructions, a 20 ft straight duct is just fine. If you end up extending beyond 20 feet, you should increase the duct size by 1 inch for every 10 feet of duct run. Remember that any 90-degree bends add about 5 feet to your total run.
One thing I’d recommend from my remodel is to install the motor in the attic. I have the motor in my kitchen and my wife hates the noise it makes. It might be quieter if it’s up there instead!
How would I go about doing that? Sorry for the dumb question.
Good to know! The Vent-A-Hood we’re considering is actually rated at 400 CFM, so I’m hoping that will be sufficient.