My existing dryer vent run enters the crawlspace behind the dryer and exits through a vent that is part of one of the normal crawlspace vents. Since the house sits on a slight slope, the crawlspace on that side of the house is very short – when I am in the crawlspace there I cannot turn over. This means that the vent is only a few inches off the ground.
I was told by a contractor who cleaned out our air ducts that this was a fire hazard as leaves could accumulate and warm air exiting the vent could cause a fire. He also noted the vent in the crawlspace was a flexible type and that was bad (I understand and agree).
First question – is it really critical to move the vent so it is more than a few inches above the ground? If not, I will replace the flexible dryer vent with the 4" galvanized tube and call it good.
Assuming that I need to move the vent, I don't think I have any good options due to the length of the required run. As you can see from my diagram below, the dryer is not against an exterior wall and there is a door between it and the nearest exterior wall. The furnace is to the right of the dryer and that prevents me easily running the vent to the front of the house. Moving the dryer is not practical because I'd have to run electricity to the new spot, and unless I also ran plumbing I'd have the dryer and washer in different locations.
I considered running a vent through the roof but I understand that is not advisable due to the height of a vertical run.
It looks like my best option is to go over the door to the left of the washer and then out through that exterior wall. The total length of that run would be about 18 feet, plus two 90 degree bends, plus two ~ 30 degree bends, which by my calculations, works out to about 33 feet of effective length. This does include an 8 1/2 foot vertical run. Is this acceptable?
If that is acceptable, then I will need to exit the exterior wall (aluminum siding), at l east 12 inches below the eaves. Any guidance on how to do this? All the online guides I see have it going through the rim joist, which won't work for me b/c the water heater is in the way.
Best Answer
International Residential Code (IRC) says the maximum exhaust duct length is 35 feet. However, it also says that this length can be overruled by the manufacturers instructions, if the instructions are provided to the inspector.
I couldn't find anything that says the termination has to be a specific height above the ground, just that it must be 3 feet in any direction from any openings into the building. And that it should have a backdraft damper, and no screens
The code also says that the ducts must be 4" smooth walled ducts, and sections can't be attached using fasteners that protrude into the duct more than 1/8".
NOTE: Always check with your local code enforcement agency before begining any project, as codes vary from location to location.