• The overall cooling capability of the unit
• How often the compressor will turn on & off.  “Short-Cycling” prevents dehumidifying
• Factors heavily into the energy efficiency & operating cost
• Maintenance costs over the life of the unit

Strangely enough, the most common problem encountered in existing construction is OVER-SIZED units.  In studies performed by utility companies on the west coast, one found that slightly over 1/2 of the home air conditioners checked were a ton (12,000 Btu/h) or more oversized and another company found the same in 1/3 of the home air conditioners they checked.

Why is this so?  Because the correct method of calculating the optimum size of the unit needed is rather complicated and most contractor use shortcuts to save time.  Either that, or they just don’t know how to do it properly.  MANUAL J is the universally accepted standard. It was jointly developed by the Air Conditioning Contractors of America (ACCA) and the Air-Conditioning and Refrigeration Institute (ARI).  It is a lengthy publication, and rightfully so since it factors in all of the variables that must be considered to properly size home air conditioners.

It doesn’t matter whether or not you are talking about:

• Central Home Air Conditioners
• Window Unit Home Air Conditioners
• Portable Home Air Conditioners

The requirements are the same in order to provide you with the comfort you need while minimizing the operating costs and total cost of ownership over the life of the unit.  Contrary to what your parents may have taught you, the longer that home air conditioners run, the more efficient they are.  Ones that cycle on and off constantly are no dehumidifying the air AND they are eating up your electrical bill.

Our recommendations are:

• Do not try this on your own unless you have an engineering degree, a lot of time to spare, and enjoy reading 200+ page technical manuals -or- can buy or borrow a copy of Home Air Conditioning Software based on the Manual J Standard;
• If you go with a contractor, select one that specializes in Home Air Conditioners;
• Insist on getting a printout from you contractor of the Manual J data they used to calculate the optimum unit size of the home air conditioners.