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Sizing an AC Doesn’t Mean Exactly What You Think

tools-on-ac-unitWe can list many reasons why new air conditioning system installation must be left to professionals. One of them is only experienced HVAC technicians can do the calculations necessary for proper new cooling unit sizing.

What does sizing mean? It sounds like the technicians are taking measuring tape to find out how large the AC can be so it will fit into the space available. Which does sound a touch silly. Of course, a new air conditioner must be the right size to fit in a house, but why hire professionals for a job anybody with measuring tape could do just as well?

That’s not quite what sizing means

Air conditioning professionals will make sure whatever new AC system goes into a house fits into the space—which usually means the existing HVAC cabinet—but this is a minor step. The actual job of sizing a new air conditioning system is something different. It means matching the cooling load of the new air conditioning system to the cooling needs of the house. In other words, it means finding out how powerful an air conditioner a specific home needs for comfort.

The cooling output of an AC is measured in tonnage, which has nothing to do with how much the system weighs. (This adds more confusion to the meaning of sizing.) One ton of cooling power is equal to removing 12,000 BTUs of heat per hour. This is enough heat to melt one ton of ice, a measurement dating back to the nineteenth-century production of ice along the Hudson River, which is why the term ton is used. You learn some weird new fact every day.

When HVAC technicians arrange to install a new air conditioning system in a home, they must determine the tonnage requirement for the AC to keep the space comfortable without wasting energy; i.e. they must size the new air conditioner. For most residential homes, tonnage ranges between 1.5 to 5 tons. The square footage of the home is one important factor in sizing, but technicians use many others: how many people in the house, the number of windows and the directions they face, the heat from lights and appliances, and the speed of heat gain through the walls. All these factors go into a load calculation that tells the installers the cooling tonnage necessary for effective and efficient air conditioning.

Correct Sizing Is Critical

It’s easy to understand why an air conditioner with insufficient tonnage creates problems. A 2-ton AC in a home that needs 5 tons will never provide enough cooling. But what’s wrong with a system that’s too large? Why not play it safe and get a more powerful air conditioner if it’s affordable?

The reason is that an oversized air conditioner will immediately start to short-cycle, turning on and off rapidly without finishing a cooling cycle. This is bad news for the system because the heavy strain will lead to a short service life and elevated utility bills.

We’re the Clayton, NC, HVAC contractor to hire when you want the best possible air conditioning system installation. We’ll see you receive the AC that’s the exact size your house needs.

Have your new AC sized right! Comfort Master Heating & Air Conditioning, Inc. offers service throughout the Triangle Area of North Carolina.

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