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How much air can you blow into a soft drink bottle?


Te answer is none unless the


air has a way to get out of the bottle. What does that have to do with energy efficiency? Te answer is simple—understanding the basics of airflow can help you understand an important aspect of home comfort. Tink of a wood-burning


fireplace: An equal amount of incoming air must replace the warm air moving up and out of the chimney. Te replacement air may come from other rooms within the home, plumbing or electrical penetrations, from around switch and outlet covers, attic access doors, poorly sealed doors and windows, or from numerous other unsuspected sources. Tis is why a home heated with a wood-burning fireplace is usually cozy near the heat source, but chilly in surrounding rooms. In an attempt to conserve, folks


often ask if it is beneficial to close off rooms not regularly occupied meaning the supply-air registers and doors. Te idea seems logical, but the answer is almost always, “No.” Closing off the air supplies and doorways are almost always detrimental to energy savings and comfort. How can this be? A properly installed forced-


air heating and cooling system is designed for balance. A balanced


system will efficiently deliver the proper amount of airflow and the desired temperature into every room within a home. What can happen when changes


are made to a balanced system? Suppose the supply-air registers and doors in two unoccupied rooms are closed. Te overall heated and cooled living space has been reduced–it no longer includes the two closed-off rooms. Tis man- made circumstance just created a situation where the heating and cooling unit is now oversized.


If you have natural gas or


propane appliances, closing off rooms can be very


dangerous from an indoor air quality perspective.


Additional laws of unintended


consequences develop: reduced compressor life, higher duct pressures and potential for greater duct leakage, additional burden on the air-handler, and the likelihood of mold and mildew developing in the unconditioned rooms. Te unit may also run for very short periods of time, causing humidity levels to climb and comfort to be diminished. Also, if you have natural gas or propane appliances, closing off


rooms can be very dangerous from an indoor air quality perspective. Carbon monoxide can back draft from the water heater and furnace flues under certain situations. Te closed-off rooms represent


a soda bottle. Air cannot move through the room and back into the return-air grille when supply-air grilles and doors are closed. Now, let’s open the registers in these same two rooms, but leave the doors closed. No more air can blow into the rooms than can escape out of the rooms. For example, if the doors are touching the carpet and the rooms are airtight, almost no air can enter the room. If the door is tight and air still comes in the rooms, you know there are leaks in the building envelope. In other words, the money you


just spent to heat or cool just leaked to the outside. We’ve tested many homes that


were hot in the summer and cold in the winter only when the doors were closed. Properly trimming the bottom of a door to create a 1-inch air gap or installing a return-air grille in the door will often solve this problem. In conclusion, it is nearly always best to leave all registers and doors open.


Doug Rye, a licensed architect living in Saline County and the popular host of the “Home Remedies” radio show, works as a consultant for


the Electric Cooperatives of Arkansas to promote energy efficiency to cooperative members statewide. To ask energy efficiency-related questions, call Doug at 501-653-7931. More energy-efficiency tips, as well as Doug’s columns, can also be found at www.SmartEnergyTips.org.


News Magazine 23


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