This article was originally published in the September/October 1993 issue of Home Energy Magazine. Some formatting inconsistencies may be evident in older archive content.



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Home Energy Magazine Online September/October 1993

Mobile Homes:
Small Zones,
Big Problems


by Larry Kinney

Larry Kinney is president of Synertech Systems Corporation in Syracuse, New York.

In mobile homes, the furnace is typically located in a tiny room in the middle of the structure. A distribution fan at the top of the furnace moves return air downward through a counter-flow heat exchanger to a plenum that connects to a single long supply trunk. This trunk runs the length of the home between the belly board and floor (see Figure 1). A series of supply ducts connected to short vertical risers brings conditioned air from the trunk to the rooms of the mobile home. In most mobile homes, the home itself is the return air system, the formal part being only a hole in a furnace room door usually covered with a dusty grille.

For such a simple system, it would seem that little could go wrong. Yet closed interior doors in mobile homes routinely cause pressure imbalances, driving the rooms whose doors are closed positive, and the space that includes the furnace room negative. Worse, the frequent combination of leaks in mobile home ducts and belly boards results not only in low heating and cooling system efficiency, but in uncontrolled air leakage. This wastes energy and can affect indoor air quality, raise moisture levels, cause structural deterioration--or all three.

In blower door testing of mobile homes, we often find that ducts are the greatest source of leakage. So in addition to having devastating effects on furnace efficiency, ducts account for substantial amounts of air infiltration, even during the off cycle. Closer inspection of the insides of mobile home ducts (using a mirror at 45 degrees and a strong flashlight) has netted sundry trash ranging from empty beer cans to an old Raggedy Ann doll. My all-time favorite was a system with no grille over the duct in the master bedroom because, as the homeowner explained, that was the entry way for her cat!

In many cases, mobile home duct problems can be treated from inside the dwelling. These include removing trash, sealing the ends of the trunk, and sealing the interface between the risers and the mobile home floor. The latter is the most frequent problem with duct leakage and is straightforward to treat. Weatherization technicians in Indiana use thin plastic angle stock, 1 in. wide on each face, to form a kind of collar to connect the duct riser to the mobile home floor. Mastic completes the job.

The interface between the boot and the plenum is another place where leaks occur, but this job requires working beneath the structure. Finally, double-wide mobile homes frequently suffer from poorly assembled and sealed flex ducts that connect one half of the house to its twin. Usually this is a pair of supply ducts about 12 in. in diameter that connect the trunk in one half of the mobile home to the trunk in the other. Making sure they are unobstructed, well-sealed, and insulated can make a substantial difference in energy consumption, comfort, and the life of the home.


Figure 1. Mobile home duct system.



Related Articles

Checking Out HUD's Proposed Mobile Home Performance Standards (Judkoff)
Moisture and Mobile Home Weatherization (Tsongas)
Beauty and the Beast Upstairs (Legg)
Discovering Ducts: An Introduction
Duct Fixing in America (Penn)
Infiltration: Just ACH50 Divided by 20? (Meier)
Leak Detectors: Experts Explain the Techniques (Proctor, Blasnik, Davis, Downey, Modera, Nelson, and Tooley)
New Group Hunts Bad Ducts (Obst)
The New Monster in the Basement (Treidler)
Selecting an Infrared Imaging System (Snell)
Sizing Up Skylights (Warner)
Telecommuting: An Alternative Route to Work (Quaid)
User-Friendly Pressure Diagnostics (Fitzgerald, Nevitt, and Blasnik)
Duke Power's Success (Vigil)
Guidelines for Designing and Installing Tight Duct Systems (Stum)
Integrated Heating and Ventilation: Double Duty for Ducts (Jackson)
Managing Large-Scale Duct Programs (Downey)
One Size Fits All: A Thermal Distribution Efficiency Standard (Modera)
Stories from the Buffer Zone (Kinney and Stiles)
Two Favorite Test Methods, By the Book (Modera)
Will Duct Repairs Reduce Cooling Load? (Parker, Cummings, and Meier)

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