Get ducts in a row: New windows, caulk will not lower heating costs


MUNCIE, Ind. – Buying replacement windows, caulking and weather stripping are not the best ways to lower heating costs, according to one Ball State University expert on building science.

“Buy replacement windows to improve the look of your home or for ease of cleaning,” said Bill Hill, director of the Building Performance Project, a part of Ball State’s Community Outreach Partnership Center.

“But don’t buy them to reduce your heating costs.”

Time of year. This time of year, newspapers and television newscasts run stories touting the benefits of caulking, weather stripping and replacing windows, Hill adds.

The majority of warm air does not escape from the sides of a house; it flows out of the top, through the attic, and sucks in cold air near the floors.

Warm air not only rises, but it also changes the air pressure in a house relative to the outside. The difference in pressure is called “stack effect,” and it is influenced by the height of the home and the difference between the temperature inside and outside a home.

The colder it is outside, the higher the pressure difference.

The stack effect produces positive pressure at the top of a house and negative pressure at the bottom – and no pressure halfway between. When there is no pressure difference, there is no air leakage; when there is a big pressure difference, there is big air leakage.

“What this tells us is that the most important air leakage sites are at the top and bottom of houses – up in the attic and down in the basement or crawl space,” Hill said.

Recommendations. To keep floors warm and to put a lid on stack effect, Hill recommends climbing into the attic and sealing all of the holes or air leaks between the house and the attic above.

“If warm air can’t escape out of the top of the house, cold air won’t be sucked in the bottom,” Hill said.

“Air sealing is the most important thing you can do to reduce heating costs.”

To spot air leaks, climb into the attic with a bright flashlight. Study the entire area, paying close attention to the places penetrated by wires, pipes and ducts.

Darkened fiberglass is a telltale sign of an air leak. That’s because fiberglass acts as a filter and removes dirt from the air as it flows through it, Hill said.

Air leaks can be sealed with foam, cardboard held in place with caulk or plastic bags filled with insulation.

Next step. Once the attic is secured, it’s time to get your ducts in a row, Hill said. Sealing and insulating ductwork – both supplies and returns – can result in big savings on heating bills.

Furnace-warmed air traveling through a cold crawl space or through an even colder attic can seriously degrade heating performance.

Once the major problems have been addressed, windows can be caulked and doors can be sealed with weather stripping. Just don’t make these the first line of defense, Hill adds.

“A cold wind causing the curtains to move is annoying, but the wind doesn’t blow that much,” Hill said.

“Stack effect, however, is going on seven days a week, all winter long.”


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