Heat Gain: What It Is and How to Deal With It

Heat Gain: What It Is and How to Deal With ItHeat gain is a fact of life, and physics, on a summer day. The natural principles behind heat transfer dictate that heat energy will always flow from a hotter zone into a cooler one. The hotter zone is the outdoors and the cooler one is inside your house. The many ways heat can infiltrate your living spaces, overwork your HVAC system, reduce indoor comfort and increase operating costs can seem daunting. While you can never totally eliminate it, here are some typical sources of heat gain and how to reduce them.  


Windows account for 48 percent of heat infiltration. Shade windows that receive direct sun with outdoor awnings or by planting trees and shrubs. Draw curtains and close blinds during the hottest hours of the day. Solar window film rejects wavelengths of infrared light that contain heat energy while still admitting visible light.

Doors and Walls

Large exterior surfaces function like solar collectors, absorbing heat energy and increasing gain by almost 20 percent. The best strategy is to bounce heat energy away instead of absorbing it. Painting exterior walls and doors with light colors helps reflect heat and reduce gain.


Solar energy soaks through the roof and radiates through your ceiling, representing about 6 percent of added heat. Adequate attic insulation inhibits heat transmission through solid materials and cuts indoor heating. In most climate zones, attics should be insulated to an R-value of R30. For both fiberglass batts and cellulose loose fill insulation, that’s at least 10 to 12 inches in the attic.

Air Leaks

Small gaps and cracks that admit air also admit heat, representing 13 percent of added heat. Caulk cracks around window frames, joints between walls and ceilings, and around any outdoor penetration points for pipes or vents. Renew weatherstripping to close gaps between movables surfaces of doors and windows.

Internal Sources

Operating major appliances and using incandescent light bulbs increases indoor heat by 14 percent, so upgrade to more efficient bulbs and appliances when you can.

For more on reducing heat gain and associated cooling costs, contact Cool Power AC.

Our goal is to help educate our customers in Hauppauge, New York and the Long Island area about energy and home comfort issues (specific to HVAC systems).  For more information about heat gain and other HVAC topics, download our free Home Comfort Resource guide.

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