Properly Sized HVAC Systems Save Money
By Rob Fanjoy

The trend toward tightening the building envelope has been good for U.S. homebuyers, as they have realized great savings in heating and cooling their homes. If the trend of properly sizing HVAC equipment had started at the same time, however, those savings could have been even greater.

Properly sizing HVAC units doesn't require any special equipment or construction techniques. It's just a matter of paying attention to the airtightness of the building envelope and selecting and sizing the equipment accordingly. Builders should throw out the old rule-of-thumb techniques and order accurate load calculations from contractors who use Air Conditioning Contractors of America Manual J (or equivalent) and ACCA Manual S. These calculations typically cost between $100 and $200 per hour and take about two hours to perform on most houses.

"Right-sized" HVAC equipment can save homeowners money and can create a more energy-efficient and comfortable home:

Smaller HVAC systems usually cost less to buy, and those savings often spur people to upgrade to high-efficiency equipment. The money saved also offsets the cost of the professional load and sizing calculations.

Properly sized equipment operates longer at maximum efficiency; oversized equipment runs for shorter periods (short cycling). It's similar to a car getting worse mileage in stop-and-go traffic.

In warm, humid weather, HVAC systems also remove moisture from the air. Oversized systems remove less moisture due to short cycling, leaving the indoor environment more humid.

Properly sized equipment will last longer, as it will start and stop less often.

Digging deep for green
Geothermal heat pumps (sometimes called geoexchange or ground-source heating and cooling) can often be one of the most expensive and complex HVAC systems for builders to consider — but they also have the biggest "upside" in terms of energy savings and environmental consciousness. They use the earth's natural below-surface temperature of about 55 degrees to provide heating or cooling to spaces above ground.

A geothermal heat pump uses a piping system (known as a loop) to collect underground heat and move it to the house, where electric compressors and heat exchangers concentrate the heat for distribution throughout the house. In warm weather, the system works in reverse, moving heat out of the house in the same way that refrigerators remove heat from their interiors.

According to the NAHB Research Center, geothermal equipment can cost $1,000 to $2,000 more than conventional HVAC equipment. Like many other alternative energy solutions, geothermal heat pumps are eligible for several federal and state incentive programs across the country, including tax credits and reductions. These incentives may have something to do with their steady rise in popularity: Over the past five years, unit sales have climbed at an average of more than 22 percent each year — an increase of more than 10,000 units annually, according to the Geothermal Heat Pump Consortium, Inc.

Customers who have these systems tend to find them worth the investment. According to the Geothermal Heat Pump Consortium, surveys conducted by utilities across the country indicate that more than 95 percent of all geothermal customers would recommend the system to a family member or friend. And the U.S. Environmental Protection Agency estimates annual heating savings of as much as 70 percent and cooling savings of close to 50 percent.

Rob Fanjoy is the former editor of Smart Homeowner magazine. He is in the process of remodeling his own Michigan home for greater energy efficiency.