Heating Your Home With a Clothes Dryer

Nov 26 2007

The House Detective by Barry Stone, Certified Home Inspector

Dear Barry: In a past article, you said, “It is not legal for a clothes dryer exhaust vent to terminate within the confines of a building….” and you cited Section 504.3.1 of the Uniform Mechanical Code. Does this mean that the dryer vent diverters sold in hardware stores and used to provide extra heat in a home are illegal too? Marshall

Hello Marshall: Several companies are currently marketing clothes dryer vent diverters. These fixtures consist of a vent duct connection and a small water reservoir. As the dryer exhaust passes through the diverter, the moist air from the clothes dryer vents into the room, while the lint is captured by the water in the reservoir. Manufacturers such as Dundas Jafine praise these devices as sources of indoor heat in winter. Advertising claims include “No need to drill holes to vent your dryer….” and “Ideal for apartments, condominiums and mobile homes.” What they fail to mention is that the building and mechanical codes specifically require that clothes dryers be vented to the exterior.

There are three primary reasons for exterior venting of a dryer. With a gas dryer, the primary issue is safety because the exhaust contains combustion byproducts that could be dangerous to breathe if vented into a home. The manufacturers of dryer vent diverters are aware of this and only recommend use with electric clothes dryers. But the likelihood that some homeowners will install diverters with gas dryers is undeniable.

Another problem with dryer vent diverters is moisture condensation in homes. All of the wetness in the clothes that were just washed is being expelled from the dryer vent. In dry climates, this added air moisture might be an advantage. In areas with moderate to high humidity, the moisture from a dryer could promote condensation and the growth of mold.

The third problem is the potential for lint build-up in the home; a potential fire hazard. This can occur if the water level in the reservoir is forgotten and allowed to evaporate. Lint can then bypass the diverter and vent into the home.

The building code prohibits the installation of unapproved fixtures in mechanical systems, but it does not prevent manufacturing companies from producing and selling such items. Other examples of products that enable homeowners to violate the building code are corrugated connectors for the drain pipes under sinks, submersible refill devices for toilet tanks, and electrical outlet adaptors that enable you to insert three-prong plugs into two-prong wall receptacles.

The free market allows these devices to be made, but the authors of the building code have good reasons not to sanction their use.

The House Detective is distributed by 1000WattConsulting. Do not republish without written consent. To purchase reprint rights please contact marc@1000wattconsulting.com

Questions regarding home inspection please email Barry Stone at questions@housedetective.com


  1. Barry- everything in your article makes good sense, but I still see some valuable and beneficial uses for a dryer vent diverter. The bathroom/laudry area in my house was always a bit colder in winter due to cold air leaking in from the dryer vent. The exhaust venting was routed behind the dryer, into a house/garage shared wall, and then took a short path into my garage where it was visible, and then out thru the siding. By placing a diverter in my garage, I eliminated all cold air from leaking into my home when the dryer was not in use. When in use, the garage gets the bonus of otherwise wasted heat. Given I have an electric dryer and live in the NE where it is cold and dry in winter, I see no concerns with either fumes or excess mosture build up. Lint is not an issue as long as you maintain the diverter with water, and any lint would be in a garage, not the house. I agree with you in principle, but think there are some times when a diverter can make good sense.

  2. Hello Ric,
    I agree that there are practical advantages to a dryer vent diverter and that adverse effects can be prevented by maintaining the water level in the reservoir. Those who use these fixtures, however, should be aware that they are not in compliance with code requirements for dryer venting. As long as that is understood by users, every homeowner can make an informed choice regarding the use of vent diverters.

  3. I would like to buzz up this entry on Yahoo! buzz.yahoo.com

  4. Ric,
    Be my guest: Give it the buzz!

  5. Thanks for information, I just wanted to know more about cleaning of Clothes Dryer Vent.

  6. WOW – Through my many cloths dryer venting installations I contacted three clothes dryer manufactures and from my background as a Mechanical Design Technologist you are right Barry (if I may) about these installations… In addition, from my experience, most clothes dryers are installed in poorly or non-insulated basements – the very last place you want to increase the humidity any time of year. Also, blower and housing designers working for manufactures I contacted all told me that the warrenty documents all note that an Equivalent Duct Length of 20 feet is the maximum for their products. You must deduct 5 feet of EDL for each 90 deg. elbow. So once your duct leaves the back of the dryer and turns upward (with 1-90 deg, elbow) runs up teh 8 ft. wall and turns again to exit the wall (usually at the header) then continues through the wall and terminates at a wall louver or hood (deduct another 5 ft. EDL for the louver) you have reached the maximum length of duct for that appliance. Any more ducting and your clothes will take longer to dry due to ari pressure loss from the duct. Only air-tight smoothwall matal duct can be used, ie. no flex ducting at all.

    Terry Ethridge on

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Barry Stone

Barry StoneKnown today as "America's House Detective," Barry advises readers from coast to coast about home inspection and real estate disclosure, providing honest clarity, fresh wit, consumer protection, and even-handed fairness in his responses to real estate questions. Read more.

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