# How to Determine Air Return Size for a Heating and Cooling System
Your heating and cooling system pumps air through an element to keep your home at the temperature you want it. It gets the air by recycling air from your home through an air return -- a vent where air that has changed temperature gets pumped into your HVAC ducts and returned through the system. The best way to find out how large a return you need is to base it on the amount of air your system pushes through.
Things You'll Need
- Measuring tape
Instructions
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By Main Supply Duct Size
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1
Find the main supply duct. This is the large duct leading away from your HVAC unit to supply the building.
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2
Measure the width and height of the heating and cooling system's main supply duct.
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3
Multiply the width by the height to determine the area of the main supply. If your main supply duct measured 10 inches by 24 inches, the area would be 240 inches.
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4
Your air return duct should have an area of at least that size. A larger return -- for example to match a standard grate size -- is no problem. Smaller returns, however, can make your system operate below its capacity.
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1
Ventilation
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