Thread: Dryer vent greater than 4"

All the codes and manf. specs seem to only list a minimum vent size for dryers. Is there anything prohibiting it from being larger?

The one I just ran across starts as 4", transistions to 8" and then back down to 4" before it goes outside. All of it's done with nice smooth thick gauge metal and installed nicely. The size is just odd.

Similar Threads:

• dryer vent
• Who needs 6" of clearance for single wall
• White "powder" at furnace exhaust tube
• Gas Dryer in Bathroom
• Porch Re-Roof - How Should This Be "Flashed"

For a building code, I think you may have to use M1502.3 which says the diameter shall be as required by the dryer's listing and manufacturers installation instructions.

I've looked at a couple sets of specs and they just all say "minimum of 4 inches"

Even aside from code or instructions, what do you think? Slower moving air, more condensation because it's cooling more quickly and there's more cold metal surface area? It's just one of those things that seems dumb but I'm struggling to find a source to cite.

Matt,

Seems to me that lint will drop out as the airspeed decreases. Might be more prone to clogging. At least the increase/decrease that you mentioned. Larger would allow air to move more freely.

Originally Posted by Gunnar Alquist

Matt,

Seems to me that lint will drop out as the airspeed decreases. Might be more prone to clogging. At least the increase/decrease that you mentioned. Larger would allow air to move more freely.

When the lint decreases the diameter the airspeed will increase. Self healing .

I am just gonna guess that it is not new construction...

I probably would not waste much time on this, since it is seen very rarely (I never have). I would probably just write it up as being unconventional, and let them know that you have no way of knowing whether it will function well as installed.

Code writers/ manufacturers can't think of every idiotic installation out there. Otherwise, I'm sure it would make it in there.

I'm going to say it is a problem based on this:

From the 2006 IRC.

- M1502.5 Duct construction.

Exhaust ducts shall be constructed of minimum 0.016-inch-thick (0.4 mm) rigid metal ducts, having smooth interior surfaces with joints running in the direction of air flow. Exhaust ducts shall not be connected with sheet-metal screws or fastening means which extend into the duct.

Where the 4" transitions to 8", okay, maybe, but I doubt it, but ... where the 8" transitions back down to 4" - that is not going to cut it. That is going to create a problem.

If someone was to say differently, the only person with any standing to do so would be a letter from the manufacturer, or their letter head, stating that was allowed or not allowed.

I doubt if you could get a dryer manf. to say one way or another.

While I think it is odd, I don't see anything in the code that says it's OK, or that it's NOT OK. The 8 to 4 transition is actually pretty smooth, so I'm not sure that would be a problem there. Since the surface is angled, I don't see where the problem would be.

Like I said, I think it is odd though.