It is well known among energy professionals that the largest facilitator of heat loss in homes is air leakage to the outside. Heat moving on air (convection) can be swift and is typically more cost-effective to reduce compared to stopping the heat loss through solid objects (conduction) such as walls. There are many points of heat loss associated with air leaks (called thermal bypasses) that are often not obvious to the homeowner. Some of these include pipe chases that run from the basement to the attic, interior dividing walls, air space surrounding the chimney, electrical penetrations, air ducts, recessed lighting, the rim joist (which rests on the sill plate along the foundation) and the band joist (which caps the ends of floor joists supporting second and third floors).
Historically, and even today, many new-home builders and those who do remodeling don't recognize thermal bypasses and the importance of making sure that construction minimizes heat loss through these bypass air leaks. This is why the new building codes are important and why weatherization programs that offer rebates are focused on air sealing existing homes.
The best approach to air sealing a home is to begin with a blower door test, which allows you to determine how leaky your home is, and to combine this test with an easy infrared scan to identify where the largest leaks are located. The blower door test also provides critical information regarding air exchange rate of a home to make sure minimum ventilation requirements are met for occupant health and safety.
Once you have identified house leaks, you can use a variety of materials and techniques to seal, or weatherize, them. Spray foam, rigid foam board, sheet metal, caulking (including high-temperature caulk), and duct mastic are some of the materials used to block holes and seal cracks.
While on the subject of weatherization, I thought is might be helpful to clear up some of the confusion regarding the MassSave and National Grid-sponsored rebate program. There were major changes in the implementation of the program at the beginning of 2010. As it stands now, if you heat more than 50 percent of your home with natural gas, you are eligible for free air sealing and for a rebate of 75 percent up to $2,000 for insulation. The administration of the program is handled by one company located in central Massachusetts. However, you can also start the weatherization and rebate process by hiring a local contractor to do both the free air-sealing and the subsidized insulation; simply go to the list of authorized weatherization contractors at the MassSave website at www.masssave.com/residential/heating-and-cooling/get-the-facts/participating weatherization contractors. Call the contractor(s) of your choice; they will visit with you and handle the paperwork, including sending weatherization recommendations for your home to the MassSave program administrator.
For more information on thermal bypasses, go to www.energystar.gov/index.cfm?c=bldrs_lenders_raters.thermal_bypass_checklist
For more information on the MassSave/National Grid weatherization program, including rebates, go to www.masssave.com/residential/heating-and-cooling/find-incentives/
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Tim Gould is director of Energy Egghead (www.EnergyEgghead.com), an Amesbury-based home improvement company that provides thorough energy audit and conservation services, 978-388-6349.