This may be a stupid question... but...

I know code limits dryer vents to 35 feet, IRC M1502.4.6.1 (https://codes.iccsafe.org/content/IRC2021P2/chapter-15-exhaust-systems#IRC2021P2_Pt05_Ch15_SecM1502). However, there is another section (M1502.4.4) that says Dryer Exhaust Duct Power Ventilators can be installed according to the manufacturer's instructions. M1502.4.5 prohibits booster fans.

I'm probably confused, but does a dryer exhaust duct power ventilator do the same as a booster fan? Does a dryer exhaust duct power ventilator allow for the extension of a vent?

As I write this, I have to wonder if the power ventilator allows you to maintain the calculated distance of 35 feet if there are multiple bends that would otherwise be subtracted from the actual physical distance.

In essence, the measured physical distance must be 35 feet, but the calculated distance due to bends would be greater than 35 without a power duct ventilator.

I'm really trying to understand IF there is a way to extend a dryer vent beyond 35 feet or if 35 feet is the absolute maximum (unless manufacturer states it can be longer).

1 Answer 1


Yes, you can extend past 35' actual length with a DEDPV

You can indeed extend a dryer exhaust past an actual length of 35' by using a listed dryer exhaust duct power ventilator (DEDPV) -- this is given in IMC 504.9.4.3 and IRC M1502.4.6.3, both of which refer you to the DEDPV's instructions for the maximum equivalent duct length permitted in this situation. (For the most common DEDPV, the Fantech DEDPV-705, this figure is specified as 125'.)

As to the difference between a booster fan and a DEDPV...

A domestic ventilation booster fan is just that: an ordinary fan, designed to mount in-line in ductwork. However, the hot, lint-laden exhaust of a dryer poses fire hazards that (say) bathroom exhaust air does not, so UL specifies extra testing and controls in the UL 705 ventilator standard that only apply to products listed and labeled as DEDPVs (this is found in Supplement SA to the standard, for the curious).

These include:

  • either an automatic activation means that turns the fan on whenever the dryer is running or an outright interlock that prohibits the dryer from running when the fan is not running,
  • a malfunction indicator and/or alarm,
  • access provisions to permit cleaning of the fan impeller and connecting ductwork,
  • a cutout to shut down the ventilator if excess exhaust temperatures are encountered (indicative of a burning dryer),
  • minimum and maximum air velocity requirements to ensure proper performance of the ventilator when installed as per its instructions,
  • and testing to verify the lint-handling ability of the ventilator design.

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