Is it OK to run Flexible Metal Vent through a wall, that is hooked up to a gas dryer?

Question

I recently bought a gas dryer. After hooking up the exaust, I read in the manual... "do not install flexible metal vent in enclosed walls, ceilings or floors." Does this mean I cant run the flexible metal vent that I have directly through a wall, which is no more than 6 inches in length? OR does it mean not to run the vent from the bottom of the wall to the top?

Answer 1

Don't run flex vent through a wall.  Use the real stuff.  Okay to run flex to that point.

Answer 2

You shouldn't use flexible vent hose for a gas dryer at all.  The corrugations trap lint like a magnet.  Then in theory (though I think it's probably unlikely), unburned gas or a start-up flame (which can be quite large) can travel into the tube and combust the lint.  Straight wall metal tube doesn't have this problem, because the lint can't stick to it as well (though it can stick, and will require cleaning periodically).  

Another, more likely issue is that the lint accumulation will simply block the airflow out of your dryer, which will drop its efficiency severely. Since the run of the hose through the wall is horizontal, and usually ends in a vent valve (a lint accumulator), having the corrugated stuff at this point is not wise.  The lint will build up very quickly without gravity to help it fall back down the tube.

Lastly, it will be more difficult to create a reliable air seal around a flexible vent than around a rigid vent tube.  This will allow cold air to enter the home, or escape the home (in summer) and raise your cooling/heating costs (a little tiny bit).  

The best compromise, if you don't want to engineer rigid vent tube all the way from the outside to the dryer itself (which admittedly takes some precision in measuring and cutting and selection of angle pieces), is to use rigid tubing through the wall, and connect it to flex tubing inside the house and run that to the dryer.  Most of the home stores actually sell the outside flapper vents (you'll need one of these unless you like cooking squirrels in your dryer) with about a 12" section of rigid tubing already installed.  So you just buy one of these, push it through your wall from the outside, s***w the flapper vent to the outside of your home, and run flex line from the (now protruding inside) rigid vent tube to the dryer.  This makes it actually easier than using flex tubing through the wall (which you'll have great difficulty attaching a flapper vent to), and it's "more right" to do it this way.  Last one I bought was $8 at Home Depot, for the flapper and rigid through-the-wall tube already attached.