If you're thinking about increasing the comfort level of your home by replacing your old central air conditioning or heat pump system with a new high efficiency one, be sure to replace the entire system, not just half of it. Otherwise, you may not get the performance you expect. So states the Trane Home Comfort Institute, a consumer information service on heating and cooling.

According to the Institute, most central air and heat pump systems are "split" systems, meaning they consist of two halves: an indoor unit or coil that pulls heat from inside air; and an outdoor unit or condenser that releases that heat to the outside air.

To obtain optimum energy saving and comfort levels, the indoor and outdoor units should be replaced at the same time. Far too often homeowners only replace the outdoor unit and neglect replacing the indoor unit. As a result, the new system doesn't always live up to their expectations.

They don't get the desired results because the indoor and outdoor units are designed to work as a team. They are matched in both capacity and efficiency when first installed and should be matched again when replaced.

Replacing an old outdoor unit with a new high efficiency model without replacing the indoor unit with an equally efficient model will simply not produce the desired performance.

Replacing both units will increase the initial cost of replacing the system. However, Trane Home Comfort Institute experts say the increase in energy savings, comfort level and overall reliability is well worth the investment.