• Alexa L. Barnett

Math of an HVAC Unit


Nashville, TN

DISCLAIMER: This is the personal blog of Alexa L. Barnett and does not reflect any position of her employer.


Here’s a spooky math lesson in HVACs to wrap up October:

A commercial HVAC unit can range from six to fifty plus tons. A “ton” in HVAC terms is the measurable ability to heat or cool. 1 ton yields 12,000 BTU’s (“British Thermal Units”) per hour. A BTU is the amount of energy required to raise or lower the temperature of a pound of water. Meaning, one BTU will heat or cool one pound of water by one degree Fahrenheit.


Here’s a formula to know the right size unit (in tons) for a commercial space:

[(SF of space*25) / 12,000] - 0.5


If a unit is too small, it will waste energy and raise utility costs. Too big, it will use more power to run than is necessary without ever achieving maximum efficiency.


Alexa L. Barnett is the Assistant Property Manager at Baker Storey McDonald Properties, Inc.