DIY HVAC Ductwork Sizing
Sizing ductwork correctly is crucial for adequate airflow to the specific living space. Ductwork that is too small will not allow enough air to enter the space and depending on the season, you will encounter either a hot or cold room. On the other hand, ductwork that is too large may allow too much air to enter the space and it may heat up too much in the winter or get too cold in the summer. Does this Spark an idea?
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Things You'll Need
- Tape measure
- Calculator
- Duct calculator
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Instructions
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Measure the room and multiply its width and length together to calculate the square footage.
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Allow 1 CFM (cubic feet per minute) of air for each square foot of space. So if you have a 200-square-foot room, that room requires 200 CFM of airflow.
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Pull out your duct calculator and line up the required CFM with the friction loss value of 0.1 to find out what size duct you need. If you used the example above, note that the duct calculator shows you can use 8-inch duct to supply the space.
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Tips & Warnings
You may also use an online duct calculator to size your duct. See resources below for a link to an online duct calculator.
For rooms with a heavy energy load (conference rooms, rooms with many windows, computer rooms), allow 2 CFM per square foot of space.
References
- Timothy Gonyo; Air Flow, Inc.; Milwaukee, Wisconsin
- AriCo Plumbin, Inc.: Sizing Air Conditioning Systems
