One industry expert says homeowners would be very surprised what may be lying in their air ducts. Anywhere from toys kids have dropped down vents to dead mice that may be blocking air flow and reducing the effectiveness of home heating and cooling systems.

When it comes to heating and cold air return ducts, industry experts recommend giving them a good cleaning every three to five years.

"It used to be nobody did it," said Tim Lantinga, vice president of Modernistic, which serves the Tri-city area and Mount Pleasant. "Now homes are built much tighter to save on energy. Houses don't breathe like they used to."

Lantinga explained that in the old days, houses naturally had more of a draft, but now the push is to build homes tight to help save on energy.

"Energy is expensive," he said. "Houses are built like an envelope now, so what happens is everything that comes into your house gets trapped in your house."

This includes external or environmental elements as well as human skin dander, dead skins cells, pet dander and dust.

"All of that has no place to go and it ends up collecting," Lantinga said. "A lot of stuff gets trapped and your furnace system ends up re-circulating it."

According to the U.S. Department of Energy, 25 to 40 percent of energy used for heating and cooling is wasted because contaminants cause furnaces or air conditioning units to work harder and shorten the life of your system.

Lantinga said that when ducts get dirty, they start narrowing the opening and therefore it's harder for air to move through properly.

"It doesn't flow through as smoothly and it should," he said.

On average duct cleaning takes about two to three hours and costs about $300.

"It really depends on the size of the house and your setup," he said.

There are a variety of different kinds of equipment that is used to clean ducts including portable machines and units that are connected to trucks. Lantinga added that the latter is much more effective.

"There's a tremendous difference," he said. "With our equipment it goes straight to the truck to collect everything. We use compressed air and brushes or whips that really clean everything out the way it needs to be cleaned out."

Lantinga said the brushes and whips both do a powerful job at pushing all the debris out of the ducts.

Aside from dust and other environmental contaminants, Lantinga said he and his team have found a variety of items stuck in vents when it comes time to clean them out.

"Kids like to throw toys down the vents," he said. "It's amazing what we find sometimes… stuffed animals and all kinds of toys. Kids will hide stuff in vents so you can imagine what we might find. It seems like a good hiding spot but then they forget about them."

Lantinga said they also find other not so fun items like dead mice in duct spaces and that can really affect the output of a furnace, adding that the average home collects up to 40 pounds of dust alone each year.

By keeping the ducts cleaned on a regular basis, families are guaranteed a much better living environment.

"It really does make a difference," Lantinga said. "It helps your furnace work more efficiently."