We live in a Dallas Texas suburb where as you can imagine it gets really hot! Hot sun, hot winds, hot in the daytime, hot in the nighttime.  It's just plain hot!

• Our 1964 sq. ft. (approximately 1100 - 2d floor, 864 1st floor) two story, brick home is currently heated and cooled with two seperate central units and managed with two programable thermostats. 
• The exterior walls have 3/4 foiled covered foam board between the brick and studs along with conventional insulation in the exterior walls, interior walls and attic.  
• The east facing home is shaded by a approximately 30 ft high oak tree on the south side of the front with 12 foot oramental trees are planted on the left front. 
• There are four large window in the front,  five windows on the shaded north side first floor, none on the second floor north side, three two casement windows on the south floor south exposure, four shuttered casement windows on the west facing second floor above the garage and finally one window on the second floor facing the north side. 
• Twelve foot tall ornemental trees run the entire length of the south side. 
• Fifty percent of the  west (back side) of the house is shaded by multiple trees. All windows have energy saving window film. 
• There are ceiling fans in the living room, and in all three bedrooms.  There are nine stereo components in the living room. 
• Kitchen appliances are all electric. 
• The new gas hot water heater is on the second floor.
• The central ac units are generally set at 78 degrees but due to the extreme heat index are periodically lowered to 75.
• My wife and I (and two cats) are the only occupants. 
• I am retired and home daily whereas my wife works five days a week.

My question is, would we benefit by supplementing our central air conditioning with one or more window units?  If so could you recommend a window unit sizing worksheet or guide?

All comments and recommendations will be appreciated.

Louis V. Patrick, lvpatrick@sbcglobal.net

I think it boils down to your satisfaction with the cooling you are getting now.   Can you keep your whole house at the desired temperature, or do you have spotty hot and cold places.

In my case in Indianapolis, I supplement my two ton central air with a 10,000 BTU GE window unit in my office because the loading in my office was never expected when they put in the ductwork in the 70s.  In the office, I have three computers running with large CRT monitor, two laser printers, a fax and overhead lights.  In the summer I use florescent lights, but the rest of the time I have halogen lights.   If I try to cool only using the central air, the east end of the house is about 10 degrees cooler than the west end with the office and I cannot cool down the office in the daytime. I can only maintain the temperature with the central air.  I put in a window that lasted 9 years.  It went out last month and I have tried to make it through the rest of the summer just using the central air.  I have been regretting the decision since August was the second hottest month here on record in over 100 years by 0.1 degrees.  Of course, it is not the same as Texas, but then again neither are the winters!  (See my post in the snow thrower section from a few minutes ago.)

I talked to my central air dealer and he said that a one-room window unit typically costs the same to run as central air for the whole house.  I don’t know how much of that was marketing, but when he looked at my situation he told me to get another window unit since adding ductwork may not have accomplished what I wanted.  I was surprise since he does not sell window units.

As for your comments about the trees, keep in mind that trees die.  I just lost a 60' tall maple that shaded my office during the afternoon.

I mix central and window also. Have a window in a smallish bedroom that keeps me cool at night, while the central in the rest of the (unoccupied) house is on a programmed thermostat that sets up to 80 at night, and also during the day when I'm there.

I've done this for 4 summers now, and I know I've saved money, and paid off the window unit. Definately more comfortable, since the central system is not well designed and the window unit evens out the temperature swings, plus I sleep better with the constant woosh sound.