An estimated four in 10 U.S. custom homes have improperly designed HVAC systems, according to a North Carolina-based maker of IAQ and energy efficiency systems.

Officials with Scientific Environmental Design Inc. say that while many homeowners pour over details such as kitchen cabinets, appliances and plumbing fixtures, the vast majority have little or no input on one of the most importance home features.

"One of the most important decisions for the construction of new custom homes is typically left up to multiple subcontractors who are not looking at the whole picture," said Neal Kearney, vice president of marketing for SED, which  says it ensures all parts of home environmental systems work properly.

"The environmental system for your home is critical to your family's health, comfort, safety and energy costs," Kearney added. "But there is a high probability your beautiful new home will not be comfortable, could cause health problems and will cost you a lot more to heat and cool than it should."

SED says homeowners should review the installation plans for their HVAC system and ensure that they meet standards established by groups such as the Air Conditioning Contractors of America.

"Homeowners should ask to review and approve a design that properly sizes the HVAC equipment,” Kearney said. “They need to know that the thermal envelope of the home will be sealed correctly and provide an air distribution system that is clean and stays that way.”

Some builders may prefer to work without input on home mechanics such as HVAC, but quality contractors should welcome such inquires, he added.

"A builder who cares will 'pull back the curtain' and educate his or her customer about the entire process," Kearney said. "Although there is a lot of science behind designing proper home environmental systems, it can and should be explained in clear terms to the homeowner — with full transparency and disclosure."