Fuel Gas Piping Sizing and Appliance Connections

The contractor's plan is likely inadequate. The gas load calculation must consider the total demand and the pressure drop. The total connected load is 210,000 BTU/h, which is below the meter capacity of 250,000 BTU/h, so the meter is adequate. However, the piping must be sized to deliver the required volume of gas at the available pressure with a pressure drop not exceeding 0.5 in. w.c. The longest run is 60 feet equivalent length. For a 1/2-inch black iron pipe, the capacity for natural gas at 0.5 in. w.c. pressure drop and 7 in. w.c. inlet pressure is roughly 70,000 BTU/h for 60 feet (based on typical gas sizing tables). That is far less than the 80,000 BTU/h furnace alone, let alone the combined load. Therefore, the 1/2-inch pipe is undersized. The contractor must use a larger pipe, such as 3/4-inch or 1-inch, depending on the branch. The correct approach is to size each segment based on the load it carries. For example, the main from the meter to the manifold must carry the total load of 210,000 BTU/h. A 1-inch pipe may be required for 60 feet at 0.5 in. w.c. drop. The branches to each appliance can be sized separately. The contractor should use the code's gas sizing table for the specific conditions. Also, the contractor must verify that the existing piping for the boiler and range is adequate; the addition of the new appliances may require upsizing the existing main. The plan is not code-compliant.

The flexible connector for the furnace must be listed for gas appliance connection and must not exceed 3 feet in length unless approved by the AHJ. The contractor plans a 6-foot connector, which exceeds the typical 3-foot limit. The contractor must either shorten the connector to 3 feet or less, or obtain approval from the AHJ for a longer connector. The connector must also be installed so that it does not pass through walls, floors, or ceilings, and must be protected from damage. It should be installed with a union or flange for easy removal. The connector must be sized to carry the appliance's demand. For an 80,000 BTU/h furnace, a 1/2-inch connector may be adequate if the length is short, but the contractor should verify with the manufacturer's instructions. The contractor should also ensure that the connector is not used as a substitute for rigid piping and that the appliance is properly anchored. The code requires that the connector be accessible for inspection. The contractor should replace the 6-foot connector with a 3-foot listed connector or seek approval. Additionally, the contractor should check that the gas shutoff valve is installed upstream of the connector and is readily accessible.