Replacing a Basement Water Heater in Concord
A homeowner in Concord is replacing a 50-gallon atmospheric gas water heater in a basement. The existing heater is 38,000 Btu/h and vents into a masonry chimney through a 6-inch single-wall connector that rises 4 feet horizontally and then 8 feet vertically. The chimney has a clay tile liner; the liner is 8 by 8 inches and serves only this heater. The new heater is 40,000 Btu/h and has a factory-installed T&P relief valve with a 3/4-inch outlet. The existing T&P discharge is 1/2-inch copper, reduced at the valve, runs horizontally 6 feet, and ends 2 inches above a floor drain. The basement has a closed plumbing system with a PRV and a backflow preventer at the meter. The homeowner wants to reuse the existing vent connector and T&P piping to save money. The local inspector has asked for a code review before approval.
1. Evaluate the proposed reuse of the existing T&P relief valve discharge piping and state what must be corrected.
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The T&P discharge is not acceptable as proposed. The relief valve outlet is 3/4 inch, but the pipe is reduced to 1/2 inch; the discharge pipe must be at least the same size as the valve outlet and must not be reduced. The discharge must run by gravity, must not be trapped, and must terminate not more than 6 inches above the floor or outside the building. Ending 2 inches above a floor drain is close to the allowable height, but the drain cannot be connected directly to the discharge in a way that traps or restricts it. The pipe material must be rated for the temperature and pressure, and the termination must be visible and safe. Because the system has a PRV and a backflow preventer, it is a closed system; a thermal expansion tank or other approved expansion control is required. Without it, normal heating will raise pressure until the T&P valve opens repeatedly. The valve itself must remain unobstructed and not be capped or plugged.
2. Evaluate the existing 6-inch single-wall vent connector and 8-by-8-inch clay-lined chimney for the new 40,000 Btu/h heater.
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The vent system must be checked against the appliance manufacturer’s instructions and the adopted venting tables; it cannot be reused just because it fits. A 6-inch connector is likely oversized for a 40,000 Btu/h atmospheric heater, and an oversized connector can run too cool, condense, and fail to develop draft. The connector must slope upward toward the chimney at not less than 1/4 inch per foot, be securely fastened, and maintain the required clearance to combustibles; single-wall connectors typically need 6 inches of clearance. The 8-by-8-inch clay liner must be sized for the appliance and for the chimney height and location. If the liner is too large, it must be relined with a listed liner sized for the heater. The chimney must be sound, lined, and used only by appliances that are permitted to share it. The inspector should require the installer to document the vent sizing and clearances before approval.
3. What gas piping details should the inspector verify at the new water heater?
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The inspector should verify a listed gas shutoff valve within 6 feet of the appliance and in the same room, a union or approved appliance connector, and a sediment trap with a drip leg at least 3 inches long installed downstream of the shutoff and as close as practicable to the appliance. The connector must be listed for the appliance, not concealed in a wall, floor, or ceiling, and must not pass through a floor or wall unless protected as allowed. The gas piping must be sized for the total connected load, not just the new heater. The inspector should also verify that the appliance is listed for the fuel gas supplied, that combustion air and venting are adequate, and that the installation complies with the adopted fuel gas code and local amendments.