It is the difference between the temperature of the air going into an air conditioner and the temperature of the air coming out, and is also called the “delta T” by HVAC professionals. A temperature split is usually determined using a probe thermometer inserted in the main return air duct just before the air handler and then at the main supply air duct at the other end of the unit. If the air temperature going in is 78º F, for example, and the air coming out is 60º F, then the temperature split is 18º F. In some systems it is difficult to test directly at the air handler and the split can be tested at a nearby air vent (register) and compared to the ambient room temperature.

   We consider the acceptable range to be between 14º F and 24º F, with 18º F to 20º F being ideal. Below 14º F means the system is performing poorly and above 24º F indicates that it is actually cooling too well, which can cause condensation at the air vents and eventual mold growth. A dirty air filter and the first stage of a refrigerant leak are two of several different problems that can cause a high temperature split.

   Although home inspectors are not required by Florida Statute (61-30.804, Standards of Practice, HVAC Systems) to check the temperature split, many inspectors, including us, do.

    Also see our blog post Why is my air conditioner not cooling enough? 

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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? 

• 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.