Air Conditioning Equipment: Repair or Replace?

Deciding whether to repair or replace central air conditioning equipment? Assess the quality of your house's ductwork and insulation first!

If your air conditioner is more than eight years old, repair is probably not worth the expense, unless it's a simple problem like debris clogging the condenser unit or a worn fan belt. To best weigh your repair-or-replace decision, ask your contractor to assess the condition of your existing equipment, and also the ducts that deliver the cool air and the overall quality of the insulation in your house. Improving those elements might increase the effectiveness of the HVAC system as much or more than installing a new system.

Assess the efficiency of your current system

Even if your central air conditioner is just eight to 10 years old, it could suck up to twice the electricity that even a low-end new one would use. That's because it operates at or below 10 SEER, or Seasonal Energy Efficiency Ratio, which is the amount of energy needed to provide a specific cooling output. Until 2006, 10 SEER was standard, but these days, the minimum allowed by federal law is 13 SEER. That translates to 30% less electrical consumption and 30% lower cooling bills than equipment installed just a few years ago.

A new 13 SEER unit will cost $3,000 to $4,000 for an 1,800 square foot house. Double your energy savings by jumping up to 16 SEER, which reduces cooling expenses by 60% over a 10 SEER unit. These super-efficient units are more expensive At $5,000 to $6,000, but they may qualify for a federal tax credit, and possibly local incentives, too.

Inspect the condition of the ductwork

Mechanicals are only part of the central air system.You could upgrade to the highest efficiency gear available and still not feel comfortably cool on hot days. The average house's ductwork leaks 10% to 30% of its air before it can reach your living space. Before deciding whether to repair or replace your condenser and blower units, your technician should run a duct-leakage test, by sealing the vents and measuring how much air escapes the system.

If the ducts are inefficient, he can locate and seal the gaps, typically for $25 to $35 per vent (per "run" in industry jargon), or replace the ductwork entirely with new, insulated pipe for around $100 per run. Your technician may recommend doing the duct improvements in conjunction with replacement of the mechanicals or may recommend only one or the other job.

Consider the building envelope itself

Resolving the house's ineffeciencies may mean that your old system will have enough cooling power to continue to do the job for a few more years. If your house is poorly insulated, it strains your aging air conditioner. 

Your heating and cooling contractor should assess and, if necessary, upgrade the building envelope. For example, seal gaps and cracks in the outer walls and attic floor, or blow insulation into the walls, either of which could knock as much as 30% off your heating and cooling costs. Insulation also may get you a federal tax credit, and may be a more effective solution to your cooling problems than replacing your equipment.

Make sure a new system is sized right

Make sure the contractor's bid includes a load calculation, which is a computer printout showing how big a system you need and why.

Air conditioning is measured by the ton, which is the cooling power of a one-ton block of ice melting in 24 hours. Some installers use a ballpark estimate for sizing equipment, one ton for every 400 or 600 square feet of living space. But, that typically leads to systems that are too big, according to some. Not only do oversized systems cost more, but they also do their cooling work too quickly, which results in more frequent on/off cycles. This can wear out key components a lot quicker. They also wouldn't have a chance to effectively dehumidify the air.

Use contractors that use load-calculating software that factor in such data as the number of windows in your house, the thickness of insulation, the configuration of the attic, and the building's orientation to the sun. It produces not only an exact tonnage requirement, but determines how much cool air each room needs. Get at least three bids from licensed well-regarded companies that include this one-page printout.