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PATH Case Study

HVAC Systems:

Size Matters

Printable Version [.pdf, 168 KB]

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Carl Seville
Principal, Seville Consulting
Decatur, Gerogia

Builder Type:

Green Building Consultant

The Technology:

Right-sized HVAC Systems

The Project:

Historic Home Renovation

This 1918 home in an historic district in Atlanta was expanded by 2,400 sq. ft. using energy efficiency principles. Proper HVAC practices significantly reduced the home's energy use and improved indoor air quality. The project won the 2006 NAHB Green Project of the Year award.

"We've been in situations where we could take a ton or more off the HVAC system by doing a careful and accurate Manual J load calculation."

-- Carl Seville


SEVILLE'S STORY HVAC and ducts are located in conditioned space because of insulation in the roof line. The unit was also strategically placed in the middle of the attic to shorten duct runs.

"When I remodel a house, I look for every opportunity to incorporate energy efficiency because I know this will result in a quality, healthy home--which appeals to every homeowner," says Carl Seville. "One key step is properly sizing the HVAC system using the industry standard, Manual J."

The Air Conditioning Contractors of America’s (ACCA) Manual J, Residential Load Calculations, is the accepted industry standard, approved by the American National Standards Institute, for the proper sizing and selection of HVAC equipment in residential homes.

"How many customers have asked for a Manual J calculation?" asks Seville. "To date: exactly none. My customers may not realize the mechanics behind the scenes, but they sure are happy with the end result."

"Properly sizing HVAC systems in well sealed and well insulated homes leads to satisfied and comfortable customers, lower initial and operating costs, reduced callbacks, and healthier indoor air quality."


"Is it faster to skip the load calculations and use a rule of thumb? Yes," says Seville. "Does it compromise the home's quality? Absolutely."

"The less time a remodeler takes to make a sale, the better off he is from a business standpoint, but to really evaluate a house you need time. And time costs. Then again, we've been in situations where we could take a ton or more off the HVAC system by properly designing a system based on insulation and air-infiltration rates--and that means significant cost savings on the equipment."

"Load calculations cost approximately $100 or $200 per house and take between one and two hours for an average home. This cost is often recouped immediately because the system can typically be downsized. If a number of homes with similar plans are being calculated, costs are even lower."


"The real pay-off for the remodeler is counted in customer satisfaction," says Seville. "When the equipment functions properly, the home is more comfortable and the air quality is better. The homeowners notice that immediately. Then they start to see the impact on their utility bills. Rising energy prices make this improvement even more valuable."

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Carl Seville

Carl Seville founded and served for over 25 years as vice president of SawHorse, Inc., an Atlanta-based residential renovation firm. Seville developed the EarthCraft House Renovation Program with the Southface Energy Institute. His current firm, Seville Consulting, provides training, speaking, and consulting services in sustainable building practices. Seville serves on the NAHB Green Building Subcommittee and the National Association of the Remodeling Industry's Green Remodeling Education Committee.

Why he uses right-sized hvac systems:

"You avoid oversizing (and overspending) on the initial installation. Utility costs are lower, the house is healthier and more comfortable, and the equipment lasts longer."

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Content updated on 9/5/2006

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