Garage Water Heater Replacement: Relief Discharge, FVIR Listing, and Flue Clearance
A 1994 ranch house has a 40,000 BTU/hr atmospheric gas water heater in the attached two-car garage. The 15-year-old unit is replaced with a new 40 gal model listed as flammable-vapor-ignition-resistant. Findings at the final plumbing and mechanical inspection: the new heater sits directly on the garage slab; the temperature and pressure relief valve has a 3/4 in outlet but is piped in 1/2 in copper that runs 12 ft with two elbows and rises 18 in through the wall, ending 8 in above the garage floor at a capped, threaded adapter; there is no drain pan and no drain line, though a floor drain sits 4 ft away; the 4 in single-wall flue connector has 1 in clearance to wood framing at the ceiling penetration, while the Type B vent above it has the listed clearance; combustion air is drawn through a single 12 in by 12 in louvered opening in the garage door at 6 ft above the floor; and the heater's cord is plugged into a GFCI receptacle on the garage wall.
1. Evaluate the temperature and pressure relief discharge piping.
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This is the most serious finding and it fails on several independent grounds, so cite them separately.
Size: the discharge pipe must be the full size of the valve outlet, which is 3/4 in here, and may not be reduced anywhere downstream. Reducing to 1/2 in chokes the discharge rate, which is exactly what the valve exists to guarantee.
Termination: the pipe must be open and unobstructed. A threaded end with a cap is prohibited, because a cap can be tightened or plugged and because the pipe must discharge freely. No threads are permitted at the outlet for the same reason.
Gravity flow: 12 ft of run with two elbows plus an 18 in rise creates a potential low point and trap where water sits, scale forms, and the line can freeze or back up. The pipe must run continuously downward or to the exterior with no trapped sections, using material rated for the relief temperature.
Termination height: terminate at the exterior or above a waste receptor or floor drain, within the distance above the floor that the edition in force prescribes. Eight inches is close to the common 6 in limit and should be checked rather than assumed.
The correction is a 3/4 in discharge, unthreaded and uncapped, draining by gravity to the exterior or to the floor drain.
2. Should you cite the heater for not being elevated 18 in above the garage floor? Address the pan and physical protection as well.
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No, and this is where an inspector can lose credibility by over-citing. The 18 in elevation exists to keep an ignition source above the heavier-than-air gasoline vapors that collect near a garage floor. A unit listed as flammable-vapor-ignition-resistant has been tested to contain ignition within the appliance under that exposure, and the listing expressly permits floor-level installation. Cite the elevation only if the installation instructions require it, since listed instructions govern, or if the listing is not documented. Confirm the listing from the data plate and the manufacturer's literature rather than a model number.
Pan: a drain pan is required where leakage from the heater or its connections would cause damage. In a garage on a slab with a floor drain nearby, that is arguable, but the manufacturer's instructions may require one and local amendments frequently do. Check the instructions before deciding, and if a pan is installed it must be at least 1.5 in deep and drain by gravity to a suitable location.
Physical protection: the heater sits where a vehicle nose or a bicycle can strike the controls. The appliance must be protected from physical damage; a bollard or repositioning is the usual remedy. Require it, and note it as a distinct item.
3. Evaluate the combustion air opening and the flue connector clearance, and state what you would require.
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The combustion air opening, examined alone, is probably adequate on area. Under the single-permanent-opening method the free area must be one square inch per 3,000 BTU/hr of total input, which is about 13.3 sq in for 40,000 BTU/hr, and the opening must be located within 12 in of the top of the enclosure and communicate with the outdoors. A 12 in by 12 in louvered opening in a garage door satisfies both, since the door is an exterior wall and the louver is high. If the appliance were in a confined space, the two-opening method and the free-area reductions for louvers would need checking, but a two-car garage is not confined by volume.
The flue connector is the real defect. A single-wall connector requires 6 in of clearance to combustible material; 1 in is a serious breach, and the 1 in clearance that applies to listed Type B vent above the transition does not carry down to the single-wall section. The framing at the ceiling penetration will pyrolyze over time.
Require the connector to be rerouted or shielded with a listed thimble and ventilated clearance, verify the draft hood is properly positioned, and re-inspect with the appliance firing and a smoke test before signing the final.