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PATH Case Study

Size Matters


Continued from Page 2


Right-sized systems reduce callbacks. That's a compelling reason for contractors to conduct Manual J calculations.

"Manual J can help remodelers and contractors properly size HVAC equipment," says Seville.

"Using Manual J, a contractor calculates heat loss from the house through walls, ceilings, and leaky ductwork, and infiltration through windows, doors, and other penetrations. Manual J also helps calculate heat gain into the house from sunlight, people, lights and appliances, doors, walls, and windows."

"Load calculation software is typically used by home raters, HVAC contractors, and engineers. Most remodelers don't own the software and perform the loads themselves. But there is always the risk that someone who knows how to use the software may not correctly size a system for a particularly well sealed and efficient house. That's why the remodeler or builder needs to be involved: to make sure that the load calculation is accurate."


Technology Highlights

This project included the following PATH-profiled technologies:

"To properly design the HVAC system, it's critical to determine how the house will be renovated and what materials will be used," says Seville. "If you change insulation types or make the house tighter or more leaky than you planned to, you may find that the system you install is not the right size, even though you used Manual J. For example, if you have the system installed, then afterwards decide to upgrade to spray-foam insulation, the system will probably be too large and it will not be the fault of the person that did the load calculation. This is because the house is tighter and better insulated than expected."

When the HVAC contractor understands the big picture, he can effectively evaluate the situation and recommend a range of improvements that provide the best solution for the client. Without this information, the contractor may simply suggest replacement equipment--and that equipment may not be properly sized.

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Content updated on 9/1/2006

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