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.
Last week, we talked about how each dryer brand/model has a unique set of duct-length specifications, how to calculate this length once the ducting is installed at frame stage, and how to determine if your dryer is capable of moving lint through the calculated duct length.
If the dryer vent duct length exceeds the maximum specified for your dryer, what are your options?
- Booster Fan – Add an inline booster fan. Long duct runs with multiple elbows can extend drying time and cause lint and moisture buildup within the dryer duct. Booster fans (as long as they can be installed in a location that allows access for maintenance) can solve both of these problems.
The Fantech booster fan pictured here (Fantech.net) can be purchased online for about 
$160.
All but one of Fantech’s fans can be used in duct runs of up to 130 feet. Their “intelligent” model also includes a wall panel with an LED to indicate when the unit is working properly.
- Select another dryer that can handle the calculated duct length. General Electric is one manufacturer that offers dryers specifically designed to address this issue (GEAppliances.com).
At first glance, adding a booster fan may seem easier than replacing or selecting a different dryer, but this is not necessarily the case. Here’s why:
- A booster fan is one more item to maintain. Without frequent cleaning, the moist hot air passing through it will cause lint to stick to the fan blades, causing them to become unbalanced and ultimately damaging the unit. In addition, a dirty booster fan is a fire hazard, so if you choose this option, be certain your fan is installed in an accessible area. You’re going to need to get to it on a frequent basis.
- If a Fantech booster fan will be mounted within 15 feet of the dryer, a separate inline lint trap, pictured here, must also be installed. The lint trap will need to be accessible from a wall panel in the laundry room and should be inspected for lint
accumulation prior to using the dryer. Be aware the wall containing the inline lint trap will need to be framed at 6” deep instead of the standard 4” or other means of accommodating the trap will need to be designed into the laundry room framing.
How are dryer vent specs handled during the construction process?
In many cases, determining the compatibility between the dryer and the duct length falls on the duct installer (when he/she is provided with the proper information). Here’s the process:
- The appliance supplier provides the specs to the builder.If a dryer is part of your appliance package and the appliances are purchased from an industry supplier, the supplier provides the specs to the builder. If you purchase the dryer from a retail outlet or will be moving your existing dryer, you’ll need to get the installation instruction manual to the builder. (Of course, if your dryer will be located on or near an outside wall, duct length is usually not an issue.)
NOTE: Appliances are one of the first things selected when building a new home. If your laundry room location will require a long duct run, ask your appliance supplier to show you possible dryers. Also ask about the possibility of switching dryers should the power of your initial selection be insufficient to deal with the final calculated duct length determined at installation.
- The duct installer determines compatibility: The duct installer (usually the HVAC company) receives the specs from the builder and determines if your dryer can handle the duct length configuration needed to reach the exterior of the home. If the two don’t match, and you’re not involved in this discussion, a booster fan may be added without ever mentioning the situation to you.
- If he/she is provided with the dryer specifications, the code inspector confirms compatibility between the dryer and the duct run during the rough-in inspection.
Of course, the building process differs around the country and from one builder to another, so these steps may or may not take place on your job site. If they don’t, you can always calculate the duct length and confirm the compatibility yourself by using the information provided in last month’s e-zine. And if you don’t have the instruction manual for your dryer, you can usually find it online by manufacturer and model number. The point, regardless of the process used in your area, is to communicate your preferences to your builder.
Take photos or video of the dryer duct as part of your rough-in documentation (see the July 2009 e-zine, “Don’t Forget the Last Step before Insulation”). Providing this documentation along with the duct-run calculations will be very helpful for subsequent owners of your home. It might come in handy for you, too, should you decide to replace the dryer while still living in this home.
Connection from the dryer to the wall. Now that the duct behind the wall is compatible with your dryer, it’s time to address the connection from the dryer to the wall.
Crushed Dryer Vent – A crushed duct dryer to wall connection—like the one shown in the 
photo to the right (courtesy of In-O-Vate Technologies, Inc.)—also means the dryer will take forever to dry your clothes (not to mention it’s a fire hazard). If moist air can’t be removed from the dryer, your clothes can’t dry.
Dryerbox – The recessed Dryerbox® product pictured here alleviates this “crushing” problem by allowing for a soft sweeping-upward connection between the dryer and the wall. If your dryer will back up to an interior wall and your builder doesn’t already use this product, ask him to order it for your job. (Under some circumstances, the Dryerbox can also be installed in an exterior frame wall, though in this case you should check the FAQ 
section of the manufacturer’s web site prior to ordering.)
For more information, visit Dryerbox.com
In conclusion:
- Avoid long dryer duct runs and the problems that accompany them by selecting a home or designing a new one with the laundry room located on an outside wall.
- If at all possible, avoid a dryer duct that vents straight up through the roof. Designs of this type require regular maintenance, including going up on the roof, cleaning out the damper, and using a leaf blower or other mechanism to remove lint trapped in the duct.
- When a long duct run can’t be avoided, select a dryer equipped to handle the calculated length. Discuss the situation with your builder at the planning stage to be sure he/she knows you intend to make the appropriate dryer selection.
- If the installation of a booster fan cannot be avoided, be sure the fan and separate lint trap (if required) are accessible for frequent cleaning.
- Specify the Dryerbox recessed dryer vent box when possible..
Dryer venting is something most of us give little or no thought to when designing a new home or purchasing an existing one, but as you can see, careful attention to this detail not only saves time and money, it also may increase the safety of your home.
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