What is the code for dryer vent length?

Answered by Jeffrey Anderson ~ October 2, 2012 ~ No Comments

Installing a dryer vent in my garage.
My garage is approx. 2 car length. What is code to vent it?

Jeffrey Anderson

The International Residential Code (IRC) states that the maximum length for a dryer vent is 25 feet, according to the National Association of Certified Home Inspectiors website. However, there are a lot of variables that can enter into the equation. That 25 feet is based on a straight run of vent piping -- if there are any bends in the line, the disruption in air flow means a reduction in total length. For every 45 degree angle in the line, 2.5 feet has to be subtracted from that 25 feet total length. If you have 90 degree bends in the line, 5 feet has to be subtracted for every elbow.

However, I have found that inspectors often rely more on the information supplied by the dryer manufacturer than the IRC code when checking line length. If you look at the installation instructions that came with your dryer, there should be a section that provides the maximum vent length the model is rated for -- manufacturers' websites usually have this information as well if you no longer have the booklet.

Some dryer models are rated for longer vent runs than others and in my experience, local inspectors often use these specifications when checking your installation. Of course, you still need to reduce the maximum length for any bends in the line and the inspector needs to see the official literature.

If you are having a problem with meeting the IRC code, my recommendation would be calling your local building inspection office to verify that they will accept the dryer manufacturer's venting specifications. This is assuming that it's longer than 25 feet.

It is also possible to add a booster to the dryer vent line in situations where it's impossible to meet maximum length. These are usually fairly inexpensive and easy to install. However, it's one more piece of equipment to maintain, so finding a way to vent the dryer that meets code using only ductwork is almost always the best choice.

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