AskCodeMan

Code Man:

When, if ever, and under which code(s) were clothes dryer vents allowed to be 3 inches in diameter?

Thanks,

Aaron, maybe before my time?

I've only ever seen 4" diameter exhaust outlets on clothes dryers, and wiyh 4" diameter exhaust outlets, the exhaust duct would need to be 4".

That said, if a manufacturer made and listed a clothes dryer which had a 3" exhaust outlet, there would be a conflict in the code (install per manufacturer's installation instructions AND the code), with the codes stating that the most restrictive applies. Which puts the codes 4" minimum as the more restrictive.

In such a case, the AHJ could use alternate means and materials to approve such "in writting", which means that there should be a record of it.

One final 'opition', which doesn’t sound like it applies: condensing clothes dryers, which would be installed in accordance with the manufacturer's installation instructions.

I haven't seen any condensing clothes dryers installed, so I'm not sure what their exhaust/drainage requirements are, bit I think they would be 'condensate drain piping'.

I looked up one installation instruction manual for a condensing tumble clothes dryer, it is drained this way:

Condensed water
- Install the dryer so the condensed water will continuously flow into a drain or sink. To do this, follow the instructions below:
- - 1 Connect the rubber hose supplied with the dryer to the blue nipple.
- - 2. Run the hose to a drain or sink, as illustrated.
- NOTE!
- - The drain hose must not be more than 40” (100cm) above the floor.

Based on the above, it is quite possible that a condensing tumble clothes dryer could be drained into the clothes washer standpipe ... as long as it was not more than 40" above the floor the condensing dryer sets on. If the clothes washer standpipe is higher, using a small platform under the condensing clothes dryer may be used to reduce the vertical height above the 'dryer floor' to the clothes washer standpipe.

Code Man
I guess the only place to hang one's hat is on the current codes and mfg.'s installation instructions.
Thanks

aaronm wrote:I guess the only place to hang one's hat is on the current codes and mfg.'s installation instructions.

Aaron, especially in the case of a newer appliance in an older construction building.

In such a case, it may be prudent to place the higher priority on the manufacturer's installation instructions as the system (in this case the clothes dryer duct) may be treated as an 'unknown'/'unconfirmed' (after all, the only visible parts would be the connection of the flexible or rigid dryer connector to the dryer duct, and the dryer duct cap at the exhaust end of the duct).

Is the clothes dryer correctly installed to the dryer duct, size and type of connector to duct)?

Is the dryer cap at the exhaust end correct?

The length (also type and size) of the dryer duct is unknown/unconfirmed.