Hi everyone, I have a range hood with solid smooth wall metal ducting from interior, through my attic to a metal roof vent with baffle The duct in the attic is wrapped with R21 fibreglass pink. The range hood drips condensation in the cold months ( never drips during rain or during warm months) there is a baffle on the range hood that I can hear open and I can hear it close when using the fan. The roof vent baffle is closed ( I can see it from outside). I believe cold outside air enters the duct and condensates when it meets warm inside air. What can I do about this? Thanks
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In winter, does it drip all the time, or only when you're using it or only right after using it?
It drips most of the time. Practically pours out when we are done using it and shut it off
I think you might have more of a thermal-bridge problem than an air leakage problem since after you shut it off, the pipe must be rapidly cooling. That roof cap sitting outside is a constant heat-sink and it's directly connected to the solid pipe, which is going to keep that pipe cold, regardless whether the pipe in the attic is insulated. An easy first thing to try is to replace the last section of pipe that connects to the roof cap with insulated-flex duct to break that thermal bridge and see if it helps.
Also, we have 9’ ceilings, the hood baffle is on top of the hood at the beginning of the pipe run up and out So from about 6.5’ or so up all the way to the ceiling (9’) the air would be warm and not baffled at all. My friend said “ why wouldn’t it always condensate and drip”
The flapper on most hoods and micro/vents is worthless at best. And a straight up pipe to roof is also not much help.
An in-line backdraft damper down close to when the pipe leaves the conditioned area might solve the problem. This will stop your constant leakage of warm inside air. A bit of horizontal wouldn’t hurt either.
@calvin - I agreed with this suggestion in my head originally, but now that I've thought about the specific problem more I don't think this is a good idea.
A butterfly damper around ceiling level would likely resolve the dripping issue when the fan hasn't been in use, because it'll keep the warmer air from entering the colder zone and condensing on the pipe or the roof cap.
But after using the hood and shutting it off (which is the worse of the problems), that damper will close and the condensation will drip down and presumably collect on top of the damper, and in very cold weather possibly freeze that thing shut. Even if it doesn't freeze, it will have collected on top of the damper and possibly dump its contents onto the stove the next time the hood is turned on.
Ok mike,
How about this. Changeover you’re hood to self venting if that’s an option. Grease filters will work as usual, no hot air up the pipe and still that lovely smell of breakfast or dinner......
Thanks for the help so far guys. For flexible duct option, is plastic okay? If so, how far from the stove top is a safe distance?
Read your instructions, but. NO PLASTIC
In all hood ducting I’ve done from the low cost nutones to those huge cfm units all have instructed no flex pipe of any kind or material. They all are “corrugated” and with all those grooves it’s a natural grease catcher. Also, at each of those grooves (metal duct) are the chance for leakage.