HVAC Tonnage Simplified: Everything You Need to Know

Bry'Ana Arvie
Written by Bry'Ana Arvie
Updated January 20, 2022
woman adjusting thermostat in house
Photo: monkeybusinessimages / iStock / Getty Images

Highlights

  • Air conditioning tonnage refers to the amount of heat an HVAC unit can remove per hour

  • You can find the tonnage of your AC unit on your model number located on your outdoor condenser

  • Proper sizing (load calculation) is important for determining comfort levels and overall efficiency

  • Square footage, insulation, ductwork, and climate zone are among the few factors you’ll need to consider to get the unit you need 

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If your HVAC technician was especially chatty during your last maintenance check-in, you might’ve heard the phrase “AC tonnage” when discussing your unit. At that time, you likely nodded along, smiled sheepishly, and understood exactly nothing since tonnage is a strange term that has nothing to do with printers and ink cartridges.

However, it’s crucial to understand how AC tonnage measurements relate to your AC unit—particularly its ability to keep your home comfortable. Keep reading; this guide covers everything you need to know about AC tonnage and how to find it. 

AC Tonnage Explained

AC tonnage measures the ability to add or remove heating energy to or from your home. A ton of heating and cooling refers to the ability of an HVAC system to melt one ton of ice in 24 hours. A one-ton HVAC system moves 12,000 British Thermal Units (BTUs) of heat—or 3,500 W of electricity—every hour.

How Do I Find the Tonnage Of My AC Unit?

How Do I Find the Tonnage Of My AC Unit?
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If you want to know how much AC tonnage your current unit has, check the label on your outdoor condenser unit. Depending on your manufacturer, they might list the exact tonnage, but most of the time, you’ll only find the BTU information, which you can use to find your tonnage.     

Here’s how you can find the tonnage information for most HVAC units:

  • Step 1: Locate your outdoor condenser unit.

  • Step 2: Find the product information label, usually located on the back of the unit.

  • Step 3: Look for the model number.

  • Step 4: Search for an even number between 18 and 60 within the model number sequence. 

  • Step 5: Divide the even number by 12 (which represents 12,000 BTU/hr, or one ton of cooling capacity) to get your AC unit’s tonnage. 

These numbers represent the BTU of your system, e.g., 18 means 18,000 BTU. Here are some examples of AC tonnage levels your HVAC may have:

  • 18 = 1.5 tons

  • 24 = 2 tons

  • 30 = 2.5 tons

How Much AC Tonnage Do I Need?

While square footage plays a significant role in determining how much AC tonnage you need, calculating the proper tonnage estimate requires you to consider a variety of factors:

  • Existing insulation

  • Ductwork

  • The current energy efficiency of your home

  • Number of stories

  • Ceiling height

  • Climate zone

Of course, these are just guidelines that’ll help you estimate how much AC tonnage you need. The best way to measure AC capacity is with a Manual J calculation by an experienced HVAC contractor near you. Too much tonnage in your AC unit will cause the system to shut off before dehumidifying an area, leaving you feeling cold and clammy. 

Why Does the Right Amount of AC Tonnage Matter?

The system's capacity needs to be quite close to the load demand as determined by the Manual J calculation. Have an HVAC pro determine the proper tonnage levels in your unit for maximum comfort, among other things.   

Comfort Levels

A unit that's perfectly equipped won’t struggle to keep you comfortable. Too little AC tonnage won’t properly cool your home. Too much tonnage will cause your AC to short cycle, meaning that it turns on and off before adequately or evenly cooling your home. 

Also, a home with too much AC tonnage won’t dehumidify as it should. A house that feels thick and stuffy most likely had more AC tonnage— or a bigger HVAC unit—than needed, leading to improper dehumidification. 

Better Efficiency and Longer Lifespan

An undersized unit will constantly run, which can cause excessively dry air and shorten the equipment's lifespan since it is running so much of the time. However, an oversized unit will tend to short-cycle. This can prevent the system from removing enough humidity, making for a damp home susceptible to mold. An oversized system that short-cycles will cause your unit to work harder than intended to keep you cool; you’ll spend more money on replacement parts or frequent AC servicing

You Won’t Overpay For Your Unit

An HVAC unit with more tonnage than you need will come with a price tag to match. While some home appliances such as a microwave and refrigerator are worth the extra cost, bigger is not better for your HVAC system. As mentioned above, it can do more harm than good. 

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