RTU stands for Roof Top Unit. Multiple RTU’s are often used on the roof of commercial building like supermarkets and big box retailers for air conditioning and heating. A simple way to explain one is to compare it to a very large window air conditioner. Everything, both the condenser and air handler, are together in one large, weather-resistant box, with supply and return air duct openings in the bottom.

    It is one of three types of “package units.” The other two are horizontal package unit and vertical package unit. A horizontal package unit looks similar to an RTU but has the supply and return duct openings on the side, and is often used at ground level for mobile homes. The vertical package unit (also called a wall mount package unit) is a horizontal one turned on end, and most often seen hanging on the back wall of retail stores in a strip mall.

    We rarely see an RTU in residential inspections, and the one shown above is actually a horizontal package unit mounted on a house roof and connected at the side to ducts going into the attic. 

    Also see What is a PTAC unit? and What is a ductless mini-split 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 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? 

• 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.