Each year, more and more homeowners are looking to central air conditioning as a means of providing comfort throughout the entire house, instead of just cooling one or two rooms with window units.

The reason is simple: a whole new generation of central air conditioning systems that feature higher efficiencies for lower utility bills, variable speed fans for quieter operation, and programmable thermostats for better temperature control.

Add to this the increased resale value of the house and you can see why the addition of central air conditioning is such a popular home improvement.

If you find yourself thinking about this type of project, a question you're probably asking is, "How easy is it to install central air conditioning in an older home?"

According to the Trane Home Comfort Institute, the answer depends on your existing heating system. If it is a "forced air" type, which has a blower and ducts, then addition of central air conditioning could be fairly simple.

All that's required is the addition of an indoor cooling coil to your furnace, an outdoor condensing unit, and the proper thermostat. Modification or replacement of the furnace blower and existing ducts may be necessary if they're too small or inadequate.

If your existing heating system uses steam or hot water, there are no ducts or a central blower. In this case, ductwork will have to be installed in the attic, basement or ceiling.

Once you've decided you want central air conditioning, the Trane Home Comfort Institute says there are four important factors to consider.

The first is the efficiency of the unit. This is indicated by its Seasonal Energy Efficiency Ratio or SEER rating. The higher the number, the greater the efficiency. The greater the SEER, the lower the operating costs.

Next is the capacity of the unit. Too large a unit will result in short operating cycles that will not adequately remove humidity. Too small a unit may not be able to maintain a comfortable temperature on the hottest days. Your air conditioning dealer can help you determine the correct capacity.

The third is the power supply. Your dealer can also help you determine if your present electrical power supply is adequate to handle the added load of a central air conditioner.

Finally, there's the overall energy efficiency of the home. To obtain the maximum benefit of a high efficiency unit, your home may require additional insulation and weather-stripping.