Q: What is the preferred method for venting the exhaust of a clothes dryer installed inside an attached garage? I have two opinions from contractors and both cost about the same, but I don’t know which to choose. The two proposals are:

One is to install the vent straight up through the roof. This involves only one 90-degree turn.

The other is to install the vent through the wall behind the dryer, which puts it inside the crawl space under the floor. The pipe would then be run to one of the crawl space vents. This requires two 90-degree turns and one 45-degree turn (venting through either of two sidewalls is not feasible in our house, leaving only the back wall or roof as options.)

Please help me choose the best option. Intuitively, the vent through the roof seems the better option with only one turn. However, I have to wonder if it is wise to vent lint-laden exhaust gas straight up. Is this a valid concern?

A: Assuming the total run of vent pipe is about the same, we’d opt for venting the dryer out the (back) sidewall. Although we’ve seen dryers vented successfully through a roof, we’d be a bit leery of this route, primarily for the reasons you mention. Even though the dryer air you need to vent is warm and will rise by convection, it’s still fighting gravity when trying to vent lint-laden air vertically.

An extra “90” in the field and a “45” near the discharge location shouldn’t be a concern. We assume the two 90s are to direct the air from the dryer into the crawlspace and the “45” will redirect the pipe to the vent for discharge to the outside. Air leaving the dryer is under sufficient pressure to move easily through the two “90s,” and the gentle bend at the discharge shouldn’t restrict the airflow.

In addition, going up means you’ll have to penetrate the roof covering. We try to avoid this to avoid possible leaks.

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