Pitch and duct on bath ventilation fan
In an uninsulated attic space how should the sheet metal ductwork, on a side discharge model, be pitched if it bends upward into back to back 90s before it exits out the gable vent? The instructions say to pitch it slightly down so condensation can drip out the dryer vent but in my run this would be toward the first upward 90 bend and not the gable vent. Is it still advisable to pitch away from the fan in this instance. I will wrap the ductwork with insulation to about R6 to minimize condensation buildup too. I want to make this right the first time because I don’t know how many more times I can do jobs twice.
They also state to start with a short piece of flexible duct to help absorb some noise as well as make the installation easier. I can see the rationale for the second point but what about the noise reduction point? The fan is a Panasonic whisper quiet fan.
Thanks
Replies
You really can not get away from that first 90 on most fan units, but after that you must give it some pitch away from the fan. Remember in that 90 you will have the most air movement right out of the fan or velocity, so your condensation will be pushed into the main run and then run down hill toward the exit point.
For me I would avoid the flex duct, it just collects dust & condensation that will just freeze up also I believe the flex duct will put more resistance to air flow for good ventilation.
Hope this helps.
Paul
Hello Paul:
Your tip makes a lot of sense and I just want to clarify. The manufacturer states to avoid any bends for the first 2-3' so I am running straight for this length to the first 90 upward bend rising ~ 6-8" to the second 90. From here it exits out the dryer vent. I will pitch this last run out the vent?
Thank you for your idea
It just so happens I'm replacing my bath fan & will look at the destructions to see what they say about the placement of the first 90 or any angles. I bought a higher end broan, 110 cfm @ 1.5 sones.
Well I just read the big 4 page manual and it doesn't mention pitch or elbow placement, maybe they figure people that are smart enough to buy broan are so smart they know how this stuff works LOL!!!
I think it really is just a common sense type thing, pitch asap & keep duct work as short as possible
Good luck to you
Paul
Paul:
I'll finish the job finally today, again thanks for the advice.
Wayne
I just put in a Panasonic whisper quiet, 60 cfm I think. It's one of the quietest units I have ever heard. It was new constuction so I tossed all the struts for mounting to the joists and framed it completely with wood, just using screws through the face flange. This eliminated all the extra rattly metal parts. Don't think you need to worry about noise with this unit.
RedfordHenry:
I have heard this about their line of fans too. Consumer Reports rated them great around 2 years ago and also said the damper mechanism is great too. Helps to keep the draft from coming in.
Wayne