Cloths Dryer Length 25' or 35'?

Standards of SOP state 25’ however other supplied specifications state 35’? Which does InterNACHI recommend?

Here is IRC 2018. Not a black and white answer.

One more thing, could you point this out in the NACHI SoP?

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The effective rating of dryer motors has increased over the years. 35’ is the standard with deductions of elbows factored in.


Thank you for the information.


Your welcome. Hope to see you around.

Hi, Jim. Welcome to the forum.

From my understanding, Manufacture trumps all for warranty and installations.
My 2 cents.

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Good morning and thanks for the input.

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I see what you mean. That is a building standard you have there, from what appears to be an education booklet. Not to be confused with the inspection Standards of Practice. Of course, building standards evolve over time or vary regionally. Sometimes InterNACHI’s education material needs updating.

Furthermore, as you likely know, InterNACHI has a published Standards of Practice we use or it may be superseded by your state’s SoP.


Dryer Vent Safety
by Nick Gromicko, CMI® and Kenton Shepard

The maximum developed length of a clothes dryer exhaust duct shall not exceed 35 feet from the dryer location to the wall or roof termination. The maximum length of the duct shall be reduced 2.5 feet for each 45-degree (0.8 rad) bend, and 5 feet for each 90-degree (1.6 rad) bend.

35’ foot is the absolute maximum with no 45 degree bends or 90 degree turns, for which you are supposed to subtract the “equivalent length” from the chart Mr. Cawhern provided. I use 25’ as my threshold for concern, presuming that there might be several bends in the line (including some that I might not be able to see).


I would go by what the appliance manufacturer recommends.

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In Florida The max is 35’ UNLESS the manufacturer states otherwise as Marcel mentioned.
Table 1502.4.5.1 also specifies other parameters.

M1502.4.5.1 Specified length.

The maximum length of the exhaust duct shall be 35 feet (10 668 mm) from the connection to the transition duct from the dryer to the outlet terminal. Where fittings are used, the maximum length of the exhaust duct shall be reduced in accordance with Table M1502.4.5.1. The maximum length of the exhaust duct does not include the transition duct.

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