Where to vent the dryer and range hood exhaust?
I am building a house with the dryer and the range located in places where it would be difficult to vent them anywhere other than through the roof or through the vented soffit at the eaves of the house. (It’s about a 40 foot run to get to the gable end)
I understand that venting an appliance through vented soffit means that the humid air will likely get sucked up into the attic where you don’t want it. However, reducing roof penetrations appeals to me and I am concerned about lint build-up being harder to deal with if the dryer is venting through the roof.
(The house is for my parents who tend to use the clothes line to dryer clothes whenever possible. Because of this, I am reluctant to have them install a ventless heat pump clothes dryer due to the high up front cost and the mixed reviews I have read on the available models.)
One option I thought of for venting through the soffit would be to install non-vented soffit for several feet on either side of the exhaust outlets to lessen the chance of humid exhaust air going up into the attic. The attic is open so air from other parts of the soffit would be able to flow freely to supply ventilation to roof areas directly uphill from the unvented soffit area. I am using vinyl soffit, so I realize that even the unvented soffit panels would probably be rather leaky at the joints.
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Replies
Timothy,
First, I'll give advice to other GBA readers: If you are designing a house, think about dryer venting and range hood exhaust venting at the design stage. Figuring out these ducting details after the house is designed and built is too late.
That said, I know that existing houses fall into a different category that new houses.
I wouldn't recommend venting a clothes dryer to a soffit or roof. As you suspected, you'll see lint build-up. I really think that a condensing clothes dryer or a heat-pump clothes dryer is the best solution in this case. Last week I was in Winnipeg, Manitoba, where I visited a superinsulated house with a Whirlpool HybridCare ventless dryer. The homeowner was pleased, and said it worked well.
It's possible to vent a range hood fan through the roof, but I don't recommend it. Depending on your cooking habits, you might get grease build-up on your roofing.
-- Martin Holladay
We purchased a LG combo washer & ventless condensing dryer (the 4.3 cu. ft. version) because we didn't want another big hole in our house and space was tight. We have been happy with it and rarely use the dryer function (we air dry clothes outside or inside depending on season/weather). I think going with some kind of ventless dryer (even if more expensive up front) would be better than a poorly setup venting one.
Same thing with range hood. If the range is electric and your parents aren't cooking greasy steaks every night...consider a recirculating range hood. In our case...we didn't even install a range hood at all because our cooking is light and not greasy. It's worked out really well and the ventilation system handles any cooking humidity.
Dryer vent pipe running through a cold attic would have copious condensation issues inside the vent.
Code also limits the length of dryer venting runs to 25 "equivalent feet". The equivalent length adds 5' per 90 degree ell, 2.5' per 45 degree ell to the linear runs. Keeping that under 25' might be hard to achieve with a roof vent even if the dryer is on a upper floor.
If you go ahead and do it anyway, use B-vent (double-walled combustion exhaust vent) for the portion above the insulation to limit condensation, and design in a means of inspecting & cleaning it with a chimney-sweep's (say, a 45' tee with a capped end). Do NOT run flex venting for any of it, except perhaps a short wide-radius turn coming out of the dryer before it enters the hard-piping, and seal every joint & seam with aluminum duct tape or duct mastic, particularly in the attic, where moisture-rich leaking air could cause problems even for a vented attic.
What about venting the dryer near the foundation? Could you run the vent line down the exterior wall?
Thanks for all the helpful suggestions. I think there is a spot low on the exterior wall where I could vent the dryer, rather than through the soffit. Is there any reason I couldn't direct the range hood exhaust downward and out through the rim joist, too? That way it would be about 9' below the vented soffit, so hopefully the moist aire would be fairly dispersed and only a small fraction would get sucked into the soffit vents.