Gas Load Check for a Tankless Heater and Range
A condo owner in a 1960s building replaces an electric range with a 65,000 Btu/h gas range and adds a 199,000 Btu/h condensing tankless water heater. The existing gas meter and 1 in. building riser serve only a 40,000 Btu/h furnace and a 35,000 Btu/h clothes dryer. The meter is rated 250 cfh at 0.5 in. w.c. drop. The range is 25 ft of developed length from the meter; the tankless is 45 ft away in a closet. The owner has 1/2 in. black iron pipe on hand and wants to reuse a 1/2 in. line that once served a grill. The tankless will vent horizontally through a sidewall with PVC and drain condensate to a laundry standpipe. The building's gas code is the DC Fuel Gas Code. The owner asks whether the existing meter, piping, and vent can handle the new appliances and what inspections are needed.
1. Perform the load check and decide whether the existing meter and the proposed 1/2 in. lines can serve the new appliances.
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Add the connected loads: 65,000 + 199,000 + 40,000 + 35,000 = 339,000 Btu/h, or about 339 cfh of natural gas at 1,000 Btu/ft3. The 250 cfh meter is undersized, so the utility must upgrade the meter/regulator or the appliances cannot be served. For piping, use the longest-length method and the DC Fuel Gas Code tables. A 1/2 in. line at 25 ft is at best marginal for a 65,000 Btu/h range and should not be assumed adequate; 3/4 in. is likely required. The 199,000 Btu/h tankless at 45 ft will need a larger dedicated line, typically 1 in. or more, with the appliance regulator set per the manufacturer. Reusing the old grill line is not acceptable without a sizing calculation and pressure test.
2. What venting, condensate, and inspection issues must be resolved before the tankless heater is approved?
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Vent and condensate details are separate approvals. The PVC sidewall vent must follow the manufacturer's installation instructions and the gas code clearances: away from operable windows, doors, intakes, and property lines, and not under a deck or within the prohibited distance of a corner. The closet must have combustion and ventilation air; a louvered door alone may not be enough. Condensate must drain by gravity to an approved receptor through an air gap or neutralizer as required; a laundry standpipe can work only if the trap is protected and the discharge is indirect. Freeze protection is needed for the condensate line. The gas piping must be pressure-tested and inspected before concealment. A plumbing permit is also required for the water heater replacement and its relief valve discharge.