Dryer Not Drying or Taking Too Long To Dry Your Clothes? (Part 1)

by tracy on April 6, 2010

Your brand new dryer—just installed in your brand new house—is taking forever to dry your clothes. What’s wrong? Could it be that the dryer and the dryer vent don’t match?

A dryer is meant to be placed against an outer wall and vented directly out of the building. If the location of the laundry room in your new home doesn’t allow for this contingency, extensive duct runs may be required to expel the dryer’s moist, hot air out of doors.

Every manufacturer provides specifications indicating the maximum duct length at which the dryer is capable of expelling moist, hot air and lint (venting). If this length exceeds the power of your dryer, the dryer will not be able to do its job.

How can you make sure the dryer and the dryer exhaust vent will be compatible in your new home?

  • Take note of the maximum duct length specified in the dryer installation manual. Duct-length specifications vary wildly among brands andez_v5_1_2 models. For example, some dryers support a maximum length of 150 feet of rigid duct, while others cap the duct length at 43 feet.
  • Based on the equivalents provided in the installation manual, calculate the length of your vent, allowing for transitions and adaptors. (Although his exercise should be done by duct installer, you can do it as well.) Elbows, transitions, and vent hoods (wall or roof caps) all present additional resistance to airflow; thus, each is determined by the manufacturer to be equivalent ez_v5_1_1to a section of straight duct. For example, let’s suppose the installation instructions for your dryer indicate that an elbow is equivalent to 10 feet of straight duct and a 2 ½ inch wall cap (see photo below) to 23 feet of straight duct. If the dryer vent in your new home is 25 feet long, with two 90-degree elbows and a wall cap, the dryer will need enough power to move lint 48 feet (25 feet of straight duct + 20 feet for the two elbows + 23 feet for the wall cap).

NOTE: Remember that maximum dryer vent duct length and transition/adaptor equivalents are different for every dryer. Thus, it’s critical that you use the duct calculation information for your specific machine.

Another factor that affects maximum dryer vent length is the type of duct material. Although the flexible metal ducting shown far right is easier for your installer to work with, it is not the recommended choice. Due to its corrugated design, metal flex duct reduces airflow and contributes to lint buildup. Over time, this lint buildup not only reduces the efficiency of your dryer, it is also a fire hazard.

Round, rigid metal is the preferred choice for ducting material as shown in the photo to the near right.

Even the dryer vent hood (wall cap) at the exterior of your home has an effect on dryer efficiency. The tight, flat, 2 ½ inch hood shown beloez_v5_1_3w on the left impedes airflow and increases the equivalent dryer duct run. For this type of vent, I’ve see the equivalency charts add anywhere from 10 to 30 feet. The curved, deeper design on the right offers less resistance; the screen over the vent ez_v5_1_4also keeps out critters. Building codes in some areas of the country state that screens should not be installed at the duct termination. For information on this vent by Heyoka Solutions, Click Here.

  • Compare the calculated total to the maximum dryer duct length specified for your dryer. After you’ve completed the calculations in Step 2 above, compare your findings to the maximum length of duct specified in the installation instructions for the dryer. If the length of the duct exceeds the maximum allowed, you have two options: Select a dryer with the capability to handle the situation or add a booster fan.

Later this week, we’ll continue with part II of Dryer Taking Too Long to Dry Your Clothes?

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