Seeking Comfort in Duct Repair

Tim Jahnigen
Supervisor, Field Sales
Baltimore Gas & Electric
Baltimore, MD

Author Ted Haskell responds: There are, of course, many measures of "HVAC performance," some of which were measured as part of RCDP (Residential Construction Demonstration Program). We didn't measure energy efficiency improvements in the HVAC equipment, or temperature rise, both of which would have been useful to know. We did measure air flows at all accessible registers and grilles. These measurements have both comfort and indoor air quality implications. Let's look at supply flows and return flows separately.

Supply flows at registers increased, on average, with air sealing. This matches commonsense expectations-if you reduce leakage in supply ducts, more air gets to the register. However, most of the time the increases were small-14 of the 20 homes measured showed total measured flow increases of less than 100 CFM (cubic feet per minute) on the supply.

A couple of homes showed significant decreases in supply flow. Interestingly, in these houses there were significant increases in the return flow measured at the grille. These houses also had significant reductions in return leakage, causing much more of the return air to flow through the grill rather than random leaks. Before sealing, most of the return air was coming from leaks. When they were sealed, the flow through the grille was less than had come from leaks, so the total flow through the air handler was reduced; hence, the flow through supplies was reduced.

On the return side, flow increases at the grille were four times as large on average as increases on the supply side. This is attributable to the fact that leaks are typically larger on the return side. This is good news from an indoor air quality point of view, since return leaks can introduce pollutants to the house from locations such as garages, crawlspaces, basements, furnace rooms, and attics. However, increasing air flow at returns may depressurize house zones with combustion devices such as wood stoves and fireplaces to the point where they backdraft. This is one reason that it's important to "test your way out" of the house when sealing ducts.

Mr. Jahnigen is right in suggesting that weight be given to comfort improvements when deciding when to discontinue sealing. It's a question of how much weight-a matter to work out among occupants, owners, contractors, utilities, and other interested parties.
 
 

Stressed-Skin Panels Stretch Resources

Harold Lorsch
Drexel University
Philadelphia, PA
 
 

Noisy Windows Irk Trailer Owner

Karl Windle
Forest, OH

Editor's reply: There is no direct correlation between thermal (heat) transmission and noise transmission through a material. For instance, thick concrete is an excellent sound barrier, but a very poor insulator, while feathers insulate well, but do little to block noise.

Still, your new window should perform significantly better than the old single-paned one, both at reducing heat loss and at cutting noise transmission. The manufacturer or distributor should be able to give you the sound rating for your model compared to others. It may be that with your newly insulated walls, you are now noticing the noise transmitted through the window more than you did before. Also, make sure that your new window has been properly installed and sealed; airtightness is one of the most important factors in reducing the noise level. Much of the noise you hear may be coming in around, rather than through, your window. Finally, try using draperies to absorb sound that does get in.

Creating Quality 
in Two Languages

Elliot Schrank
Extension Associate
Cornell Cooperative Extension
Ithaca, NY

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