People sometimes turn the central air conditioning on only at night to save money. That’s fine when the weather isn’t too hot, but it’s a bad idea when the temperature reaches 90 or so, said Mike Foraker, president of Jennings Heating and Cooling in Akron, Ohio.

Turning off the air conditioning in extreme heat lets warmth and moisture build up in the house, he explained. The unit can’t eliminate them quickly enough to make the house comfortable at night, and it uses a lot of electricity trying.

Here are some other tips for keeping cool at home with air conditioning:

» Mind the monitors. Central air conditioning works best if air can flow through the house freely. If necessary, move furniture so it’s not blocking supply registers or cold-air returns, said Karl Bella, an energy auditor who runs Energy Pros of Ohio.

Don’t be tempted by magnetic covers designed to block air returns. It may seem logical that they’ll keep the cooled air in a room, but instead they just keep the air from returning to the central unit.

Be careful about trying to save money by closing the supply registers in unoccupied rooms. Overdoing it unbalances the air flow throughout the house and results in cool and hot spots, the American Council for an Energy-Efficient Economy says.

» Minimize humidity. Don’t add more moisture to the air than necessary. Run exhaust fans when you shower, and run hot-water appliances such as dishwashers and clothes washers in the evening, the American Council for an Energy-Efficient Economy recommends.

» Seal air leaks. Cracks, holes and other openings in a house’s exterior let cooled air out and hot, moist air in. Minimize those leaks by sealing them with caulk or foam sealer. Pay particular attention to the upper areas of the house, from which conditioned air is likely to escape, Bella said.

» Install a programmable thermostat. It’s easy to forget to change the setting when you leave the house or go to bed. A programmable thermostat does it automatically, cutting your cooling costs.

» Improve your insulation. Insulation slows the movement of heat, so it helps keep cooled air inside a home’s living areas. The attic is the easiest and most logical place to add insulation, although Bella recommended considering it for the exterior walls, too. Attic insulation is especially important if the upper level of your home is hot, Foraker said.

» Add an attic fan. An attic fan boosts ventilation by kicking on when the temperature reaches a certain level and drawing the hot air out of the attic. Most are powered by electricity, but solar-powered units are available, too.

» Upgrade your system. If your heating and air-conditioning system is approaching 15 years old, it’s wise to start planning to replace it rather than waiting for a failure. Insist on an installation that meets the standards of the Air Conditioning Contractors of America. Its standards include ensuring the unit is the right size for your home and improving ducts to minimize loss of conditioned air.

Proper sizing of an air-conditioning unit is critical, Bella said. An oversized unit may cool the house quickly, he said, but it doesn’t stay on long enough to sufficiently dry the air. You end of feeling clammy instead of comfortable.