- Turn off all gas appliances in the home. If there are pilot lights they must be shut off also.
- Turn on the furnace to the highest firing rate (be careful of two-stage furnaces and variable capacity boilers, etc.)
- Once at steady-state, use a stopwatch to time how long it takes the smallest unit of measure (typically the 1/2 Cubic Foot) dial to make a full revolution on the gas meter.
- Cubic Feet per Hour (CFH) = (3600 x Dial Size) / Time (seconds)
The unit being tested takes 29 seconds for the ½ cubic foot dial to make one complete revolution. Using the chart, this translates to 62 cubic feet per hour. Based upon the assumption that one cubic foot of natural gas has 1,000 BTU’s (Check with your local utility for actual BTU content), the calculated input is 62,000 BTU’s per hour.