Furnace Terminology


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Old 08-20-05, 07:33 PM
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Furnace Terminology

Just picked up a brochure from a gas furnace manufacturer which lists "Output capacity" and "Airflow in Tons". The table shows, among others, 3 furnaces with output capacities of 47 kBTUH, 63 kBTUH and 79 kBTUH, but all three having an airflow of 3 tons. How can that be, and how do you translate tons into CFM?
 
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Old 08-21-05, 05:00 AM
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hukre

HVAC equipment and ductwork has to be properly matched in size. Yes, you can have furnaces with output capacity in the BTUs mentioned all with a 3 ton rated blower. A furnace blower (or air handler) must be at least the same size in rated tonnage as your outside AC condensor. Also, your ductwork must be sized correctly to accept and be able to carry 3 tons of conditioned air.

400CFM=1 ton

So if you have an outside condensor sized at 3 tons along with a 3 ton rated furnace blower and a ductwork system sized for at least 1200CFM of air, then you should be in good shape.

Where people get in trouble is when they decide to go up in size with their outside condensor without checking to see if blower and ductwork are sized to accept and move more conditioned air.
 
 

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