How to Calculate HVAC System BTU capacity

Bryan with HVAC School shows how to calculate the BTU capacity of an HVAC system using enthalpy. We use the UEi HUB6 kit and some simple calculations to do this.

We use two UEi WHP1 probes for the job (in the HUB2 kit or included with refrigeration smart probes and air probes in the HUB6 kit). To turn those probes on, all you have to do is open them.

Once the probes are open, go to the UEi app, select "Air side," and ensure that the probes are connected. Put the probes in their respective ducts, and you'll begin noticing that the delta T changes (and you'll see the delta T target). You'll notice two different enthalpy values between the return and the supply. The differential is your enthalpy split, which you'll use to calculate the BTU capacity (you also need to know the CFM).

After some time, we noticed that the BTU split was 7 BTUs per pound. We then use a formula to get the total heat; that formula multiplies our enthalpy differential by 4.5 and the CFM. In our case, we get (29-22) x 4.5 x 730 and can determine that our HVAC system BTU capacity is 22,995.

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