Exhaust Fan Ducts

MSSI

Does exhaust fan ducting through the attic need to be insulated by code or otherwise?...Thanks

mdshunk

No, there's nothing in the code yet. With mold being the latest hot button thing, I expect it may make it in at some point. I always run insulated flex duct for bath fans that run through cold attic spaces. I've been on too many service calls that have had water literally dripping out of the bath fan in the winter time, or have had water collected in low spots in the duct. For range hood and dryer sheet metal ductwork that runs through cold attics, I use some duct wrap. Keeping that exhaust flow warm until it gets to the wall or roof terminal is a good thing.

MSSI

Good point.. I was thinking more along the lines of problems bringing cool air (air conditioned) from the house through warm moist air in attic in summer and having water condensate on the outside of the ductwork. In turn soaking sheetrock and insulation..
Do you see a problem running insulated flex a minumum of 25 ft to "fantech's" then un isulated from there?? the un insulated runs will run up abut 2 feet from the blower then down to the soffit following the roof pitch...all other ducts will be between joists of a insulated(except roof) floored attic..Also I have one dryer run using a booster fan....Thanks

mdshunk

You're not permitted to use anything except sheet metal for dryer exhaust, per code. In fact, you're not permitted to even have any fasteners penetrating the sheet metal (screws or rivets). You need to insulate the exterior of sheet metal dryer ductwork.

MSSI

ok, thanks...Should I slope the dryerduct back towards the dryer and put a (thinking of what its called) type of trap in it? my thought is.... I have seen a type of coupling with a belly in it. I would run a piece of vinyl hose from the low point of the coupling to the washer drain which would line up about 6 feet under the dryer vent. I would put a small valve to prevent air flow but would crack it open to drain moisture periodicly....Is this a good Idea or overkill. I am installing a secondary lint trap at eye level just above the dryer as well. I appreciate any tips, look out fors.. or no friggin ways.............T

mdshunk

It's getting a little weird for me now. We'll just leave this one be, and just refer you to §M1501 in the IRC for your guidance.

MSSI

that type or drain is requried on tankless water heaters when venting horiz. with no slope..How is it wierd? not wanting water to run back down the dryer vent to the floor after it condenses.?Maybe it is wierd and Im just being anal.....Its a 35ft run its bound to condense.......