Q. What’s the right way to vent a dryer? The standard plastic flex-hose with the spiral wire always collects condensation and sags. There’s got to be a better way. Would metal or plastic pipe work?
A. Corresponding editor Paul Fisette responds: In Massachusetts, where I live, the code won’t allow use of the plastic flex pipe if the pipe passes through a wall, and code officials discourage its use in all cases. Also, several dryer manufacturers have disallowed it because it can’t stand up to the hot air coming from the dryer.
From a mechanical perspective, it’s a poor idea. First, the spiral configuration of the flex pipe creates a lot of friction in the line, slowing the exhaust. Also, the sags and turns typical with flexible pipe further reduce air flow, and allow lint and moisture to accumulate, creating blockages.
I would use a smooth metal duct. You could even insulate it to reduce condensation if you think this will be a problem (if the dryer’s in a cold space, for example). You should slightly pitch the line toward the outside if possible to allow any condensation to drain. In any case, you’ll have no sags where the moisture can collect. PVC pipe might also work for this application, but here in Massachusetts at least, you would have to provide a manufacturer’s temperature rating to the inspector to prove that it could take the heat of the dryer’s exhaust.