Maximum dryer vent height???

[Jon Randolph]

I know that M1502 of the IRC points out the max run length of 25 feet (minus 2.5/45 and 5/90), but I don't see anywhere what the maximum height can be.

1. Without having the owners manual for the dryer to refer to, is a height of up to 25' acceptable, providing that there is not a horizontal run other than the transition, which doesn't count? The exhaust in question is about 22 feet straight up and terminates with an exhaust roof cap for dryer vents.

2. At what point should a booster fan be considered?

3. Should this pipe be insulated at the point where it is in the attic (about 14' of it)?

[Jerry Peck]

I know that M1502 of the IRC points out the max run length of 25 feet (minus 2.5/45 and 5/90), but I don't see anywhere what the maximum height can be.

1. Without having the owners manual for the dryer to refer to, is a height of up to 25' acceptable, providing that there is not a horizontal run other than the transition, which doesn't count? The exhaust in question is about 22 feet straight up and terminates with an exhaust roof cap for dryer vents.

2. At what point should a booster fan be considered?

3. Should this pipe be insulated at the point where it is in the attic (about 14' of it)?

Jon,

The only real answer is the same answer Bob Harper gives to questions about factory built fireplaces, vents, etc. - 'whatever the manufacturer's installation instructions state'.

The code limit applies unless the dryer allows more, and most modern dryers do allow more, some allow up to 90 feet.

If you are questioning it, I would write it up as 'dryer vent is 25 feet vertical, provided manufacturer's installation instructions so we can verify whether that is, or is not, within the acceptable distances for the manufacturer'.