Vertically venting bathroom fan / damper / cold air
Hill_Builder
| Posted in General Questions on
New construction house one floor: The instructions state we can vent the Panasonic bath fan through the roof, (which is shortest route) but how do we stop the cold air from coming back into the house? I don’t want a cold bathroom (zone 6) and most dampers have nickel gaps around them and I am tired of listening to the damper bang every time the wind blows here. We will be in a very windy area.
Last, does well insulating the pipe stop the condensation from forming in the pipe since we can’t slope the pipe?
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Replies
Hill_Builder,
You face the same problems with possible air infiltration through the duct whether it terminates on a roof or wall. These are very effective:
https://www.tamtech.com/product/cape-backdraft-damper/?srsltid=AfmBOooje22mmwPsMF-SRktmI9_XDVA1VQfTQegODrcCFe6s62VCVpcs
The main benefit of sloping the ducts is to make sure there is no low spot for moisture to accumulate, and although you will not have a drainage path to the duct termination if you go upward, with a vertical duct there will never be a opportunity for more than an incidental amount of condensation to accumulation. And yes, insulation will help reduce condensation.
I have had good luck insulating the duct. I use rigid 4" galvanized steel duct, then pull an insulating "sock" over it. It seems to be difficult to find that round duct insulation seperately, so I usually end up buying the pre-insulated flex duct, then pulling the insulation off of the flex duct (which is easy to do), and then pulling the round insulation over the rigid duct I'm installing for the fan. It goes pretty fast and does a good job. I tape all the joints between insulation sections to make a sort of secondary air barrier so that air doesn't leak from the attic space through the insulation to the duct to help minimize condensation issues under all conditions.
Most (all?) bath fans have a damper internal to the fan assembly, but I have added secondary dampers at the far end of the duct near the exhaust vent. I don't usually have much noticeable air movement through the duct with the fan off when doing this, but the fabric-type backdrawft dampers Malcolm linked too work better than the rigid "valve" style dampers in many cases, and the fabric ones are silent when the open and close.
Bill