This article was originally published in the March/April 1996 issue of Home Energy Magazine. Some formatting inconsistencies may be evident in older archive content.
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Home Energy Magazine Online March/April 1996
Seeking Comfort in Duct Repair The information contained in Duct Improvement in the Northwest: New Construction and Retrofit (Jan/Feb '96, p. 21) on improving duct integrity in both new and retrofit situations has been very useful. I am particularly interested to find out if this study produced any results beyond energy savings. Did reducing duct leakage in existing homes also improve HVAC performance? Did the consumers express greater satisfaction with their heating systems (particularly heat pumps) following the duct sealing effort? Depending on the answer, the question of determining when to discontinue duct sealing to a particular room may rely as much on comfort as on CFM saved.
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.
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 Given that many subcontractors and construction workers are non-English speakers, it occurred to me while reading Michael Uniacke's article (Creating Quality in New Construction, Jan/Feb '96, p. 33) that having a bilingual member of the general contractor's team would also increase understanding to insure quality in new construction.
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