Remodeling offers an opportunity to replace an existing HVAC system with a unit that offers optimal heating and cooling while using less energy. In fact, if the existing equipment is more than 10 years old, replacing it with the most basic model available today can dramatically reduce utility bills.
But you may have to re-evaluate the size of the unit. "HVAC contractors often think more is better. It’s not, even for heating," says Richard Rue, CEO of EnergyWise Structures, an Arlington, Texas, mechanical engineering firm. He explains that oversizing the HVAC system can actually lead to higher utility bills, as well as moisture and mildew problems.
Here are some tips on how to minimize a homeowner’s heating and cooling costs when overhauling the HVAC system:
Size it right. Proper sizing can be more important than the specific brand of HVAC equipment. Undersized equipment won’t heat or cool properly, and behemoth systems will have higher price tags and cost more to operate because of frequent on/off cycling. "If a unit short cycles four times an hour, it’s using as much energy as it would running two hours continuously," says Richard. Longer run times allow air conditioners and furnaces to maintain consistent room temperatures and achieve more comfortable humidity levels.
Choose the most practical efficiency rating. Many older central air conditioners installed in the early 1990s have a SEER (seasonal energy efficiency rating) of only about 6 or 7. Today's units, though, have a mandatory minimum SEER of 12, and in 2006 that number will rise to 13. Some equipment boasts SEERs as high as 19.5, but these super-efficient models also command premium prices. Unless the home is in a sultry climate requiring air conditioning year-round, the owner may not be able to recoup the extra expense of a top-efficiency unit through lower electricity bills.
Similarly, modern gas furnaces must have an annual fuel utilization efficiency of 78 percent. Some deliver 97 percent AFUE, but upgrading to an efficiency rating above 80 percent may only pay off for homeowners living in areas with frigid winters, such as the upper Midwest or Northeast.
The U.S. Department of Energy provides a formula for estimating the annual cost savings for heating system replacement at www.eere.energy.gov/consumerinfo. For efficiency data on specific brands of AC units and furnaces, visit the website of the American Council for an Energy Efficient Economy at www.aceee.org.
Use variable-speed equipment. A system with a single-speed fan motor may heat or cool rooms too quickly. A variable-speed motor automatically adjusts the flow of heated or cooled air to the desired comfort level. These systems typically run longer but at lower speeds, cutting operating costs and saving wear and tear on equipment.
Install compatible systems. Remodelers may run into a furnace on its last legs while the air conditioner is just a few years old (or vice versa). If possible, replace both units at the same time. You are likely to get a discount on a package deal, and "the system will run more efficiently if all the components--including the condensers, furnace and coils--are from the same manufacturer," says Richard.
Put ductwork in insulated space. Install ducts in crawl spaces or basements (in one-story homes) or lay the ducts on the rafters and cover them with foam or cellulose insulation. The result: "For a 3,000-square-foot house, on average, you can reduce the tonnage requirements by at least 1/2 ton because you don’t have duct heat loss or gain," Richard claims.
Duct sealing. Duct tape, despite its name, is not particularly effective on ducts. It does not prevent conditioned air from leaking out of the duct and reducing the efficiency of the system overall. Nor does it keep unconditioned air from leaking into the ducts and increasing the work load for the unit. Moreover, traditional duct tape has a relatively short functional life.
More effective options include foil and fiberglass tape, aerosol sealants, mastic and the newer types of duct tape with the Underwriters Laboratory logo. Even worse is not sealing the ductwork at all, which will eliminate any benefits achieved by buying good equipment.
Consult a pro when sizing HVAC equipment. A mechanical engineer or licensed HVAC professional will take a whole-house approach: square footage, insulation of the thermal envelope, the number of windows and doors, and the climate. "In some cases, the engineer will even offer utility guarantees," says Richard.
