Q: I have a quick question after reading a recommendation you made to a couple in Fort Myers, Fla. We have a 2-1/2-ton air conditioner with a low SEER efficiency that is 10 years old. The residence is a condo. While we were away from the condo, the air conditioner started making loud noises, so the neighbor turned it off. When it was turned on again, it made the same sound. An HVAC contractor came today and said the motor/fan was shot. Two recommendations: Replace them at $819 or replace the entire unit for between $3,000 and $3,200 for a 13 SEER efficiency. The representative said the unit should go for about 12 years. Do you have any suggestion as to which way to go?
A: The SEER rating for an air conditioner or heat pump is the "seasonal energy efficiency ratio." The higher the SEER number, the more efficient the unit will be and the less energy it requires to operate. The ratio is established as the total cooling output over the cooling season measured in BTUs (British thermal units) of cooling divided by the total electrical energy input (in watt-hours) over the cooling season.
For example, let's assume you have a condo with 1,500 square feet of conditioned space. The unit would require approximately 30,000 BTUs per hour of air conditioning. Assuming the air conditioner operates for eight hours out of a 24-hour day for 150 days (approximately five months) and you have a 13 SEER air conditioner, we can find the costs to operate the unit by a simple formula: (30,000 BTUs / 13 SEER) = 2,308 watts. Convert watts to kilowatts (2308 / 1000) = 2.3 kilowatts. Using an average cost of $0.15 per kilowatt-hour, the costs to operate the air conditioner would be (2.3 x $0.15) = $0.345 per hour.
Extending our example, the annual cooling costs for the unit would be ($0.345 x 8 x 150) = $414.
If you use the same math for an air conditioner rated at 10 SEER, the annual cooling costs would be a total of $540, or $126 more than a 13 SEER unit. The cost analysis does not include the electrical use for lighting, cooking, entertainment equipment, etc., which would increase the total annual electrical usage for the building.
By using a higher SEER-rated air conditioner, you can see that the costs of operating the unit would be lower per hour. All the figures above have to be adjusted for local weather conditions, amount of insulation in the home or condo, the amount of air leakage to the building and cost per kilowatt for your area.
If you simply replace the fan motor now, sooner rather than later the compressor will fail and then you will have to replace the entire unit. You would have invested $819 in a soon-to-be-obsolete air conditioner. My recommendation would be to replace and upgrade the air conditioner to one with a higher SEER. The costs you received from the HVAC company seem to be reasonable, but get at least two more estimates before you proceed.
(Dwight Barnett is a certified master inspector with the American Society of Home Inspectors. Write to him with home-improvement questions at C. Dwight Barnett, Evansville Courier & Press, P.O. Box 286, Evansville, Ind. 47702 or e-mail him at d.Barnett(at)insightbb.com.)
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