Field and service calculators
Calculations a technician uses on a service call: clocking a gas meter, furnace temperature rise and airflow, line-set charge adjustment and cycling checks — each with its source.
Gas Meter Clocking Calculator
Measure a gas appliance’s actual firing rate by timing the gas meter’s test dial, and compare it with the nameplate input.
Answers: How do I check a furnace’s gas input by clocking the meter?
Furnace Airflow from Temperature Rise Calculator
Estimate furnace blower airflow from the heat output and the measured temperature rise, and check the rise against the nameplate range.
Answers: Is my furnace temperature rise in range, and what airflow does it mean?
Refrigerant Line Set Charge Adjustment Calculator
Work out how much refrigerant to add or recover when the installed line set is longer or shorter than the length the factory charge covers.
Answers: How much refrigerant do I add for a longer line set?
Short Cycling and Runtime Calculator
Turn an observation of on and off times into cycles per hour, average run time and duty cycle, to spot short cycling and oversizing.
Answers: Is my AC or furnace short cycling?
Tools for measurements on site
These calculators turn readings a technician takes on site into a result: the stopwatch time of a gas meter’s test dial into BTU/h input, a furnace’s temperature rise into blower airflow, an installed line-set length into a refrigerant charge adjustment, and an hour of on and off times into cycles per hour and run time.
The manufacturer’s instructions come first
Every result here is an aid to the procedure in the equipment’s installation manual, not a replacement for it. Manuals set the allowed input tolerance, temperature-rise range, line-set limits and charging method for each model. Gas and refrigerant work must be done by qualified, licensed technicians; in the U.S., refrigerant handling requires EPA Section 608 certification.