No one likes to waste money on lost energy. During the chilly nights of winter and sweltering days of summer, homeowners will be particularly interested in ways to make their home more efficient. These may range from adjusting the thermostat to home upgrades such as new insulation.

Closing off unused rooms would seem to be a simple way to reduce your energy bills. When you aren't using an office, bedroom, or other area of the home, you can close the door to keep heated or cooled air out of it. Homeowners may also close the HVAC vents in these rooms to avoid the cost of heating or cooling them.

This solution can actually cause your utility bills to increase rather than decrease. Sealing off rooms will affect the air pressure in your home, causing drafts and potentially dangerous situations.

When the HVAC system pushes heated or cooled air through the home, an equal amount of air must return back to the furnace or air conditioner. McGarry and Madsen Home Inspection, a company in Gainesville, Florida, says closing the doors and vents in a room will pressurize it and inhibit air flow into the room.

Rather than having the intended effect of keeping the room from getting heated or air conditioned, sealing off a room causes the HVAC system to work against a higher pressure. Allison Bailes, writing for the energy efficiency company Energy Vanguard of Decatur, Georgia, says this reduces the efficiency of the system and results in higher utility costs. In addition, the pressurized room will reduce the air flow in the home.

When air is forced into a pressurized room, it will force the room to start leaking through any inefficient areas. McGarry and Madsen Home Inspection says air will likely be pushed out through openings such as small spaces around baseboards, electrical outlets, doors, and windows. Closed vents can also pressurize the ducts and cause them to leak.

Since the furnace or air conditioner is not receiving enough return air from the sealed rooms, it has to draw in air from elsewhere. Doug Garrett, writing for the magazine Home Energy, says the easiest pathways for outside air to enter are through the chimney or the furnace and water heater flues. Sealing off the rooms can increase the amount of outside air entering your home by 300 to 900 percent, depending on how much space you have sealed.

An HVAC system will circulate air through a filter to remove contaminants. Bob's Heating & Air Conditioning, an HVAC company in Woodinville, Washington, says air drawn in from other sources will be unfiltered and may include dust, dirt, or humidity. Humid air can cause mold to form during the summer, and cold drafts can be a common occurrence when sealing off rooms in the winter.

The reduced air flow caused by the pressurized rooms can also cause damage to your HVAC system. Bailes says insufficient air flow can cause condensation to freeze on a cooling coil during the summer. In the winter, the heat exchanger may crack and cause poisonous carbon monoxide to leak into your home.

Garrett suggests that a closed door would need to be undercut by at least 14 inches to allow enough air to return to the furnace or air conditioner. Naturally, this would give the door a bizarre appearance and wouldn't appeal to most homeowners. Installing a duct for return air in a seldom used room could also allow an escape route while leaving the door closed, but could be costly.

A less expensive option would be a jump duct or transfer grille. These openings allow a simple transfer of air between rooms, giving air a way back to the HVAC system and avoiding any problems caused by a closed door.

Some systems may allow you to benefit from judiciously closing vents. Bailes says a system with low static pressure and sealed ducts could allow you to close some vents. In addition, closing the vents of some systems sends a signal that less air should be circulated, thus avoiding the problem of pushing through more air than can be returned. Doug Bonderund, writing for Angie's List, says you may be able to save some energy by partially closing upstairs vents while leaving downstairs vents fully open.

Homeowners can also look at other alternatives to sealing off rooms in order to save energy. You should keep up with maintenance for your HVAC system, including changing filters and regular inspections. You may consider upgrading to a more efficient system or setting up different zones so you can keep infrequently used areas of the home at a different temperature.