Generally, from an accountant’s total-cost standpoint and allowing for the time-value of the delayed expenditure for a new system, it’s less expensive to nurse your existing a/c unit until it dies. But one other factor may tip the scales toward earlier replacement: already-inefficient air conditioning systems get even less efficient as they get older, especially after about 20-years. The compressor draws more amps as it ages, and the temperature split (difference between the ambient room air and the cold air coming out the ducts) tends to decrease too. Your a/c service tech can give you a rough evaluation of the system’s current efficiency as a guide when you’re trying to decide whether to repair or replace. 

   Although the SEER rating is not marked on older units, the average SEER for a system manufactured from 1970 to 1996 was between 9 and 10, trending up gradually towards 12 between 1997 and 2006. If your current SEER is 9 or below, then a new system will be at least 40% more efficient. So replacing an HVAC system that is 20-years old or more will make a significant dent in your monthly electric bill.

   When it is time for replacement, systems with SEER ratings up to 20 and beyond, like the one shown above, are available. Each notch of efficiency means more initial outlay and, for the very high SEER systems, more maintenance because of the more complex components. For most situations, the minimum or near-minimum SEER is the most cost-effective choice; but the length of the cooling season and cost of electricity in the region can change the equation. At the southern tip of Florida in Key West, for example, where the cooling season is longer and the cost of electricity is higher than normal, a high-SEER system makes both environmental and budget sense. 

    Also see our blog post What is the SEER of my old air conditioner?

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  To learn more about heating and air conditioning systems, see these other blog posts:

• How can I find out the SEER of my air conditioner? 

• My air conditioner won't turn on. What's wrong? 

• How can I find out the size of my air conditioner? 

• How can I find out the age of my air conditioner or furnace?

• How can I tell whether the condenser (outdoor unit) is an air conditioner or heat pump? 

• Where is the air filter for my central air conditioner and furnace? I can’t find it? 

• Does an old air conditioner use more electricity as it ages? 

• How did homes stay cool in Florida before air conditioning?

• How can I find out the size of my air conditioner? 

• How can I find out the age of my air conditioner or furnace? 

•  What is wrong with an air conditioner when the air flow out of the vents is low?

• Why has the thermostat screen gone blank? 

• Why does it take so long to cool a house when an air conditioner has been off for a while? 

• Why is my air conditioner not cooling enough? 

• What are the most common problems with wall/window air conditioners?  

• Will closing doors reduce my heating and cooling costs? 

    Visit our  HEATING AND AIR CONDITIONING page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.