Water Heater Changeout: Day of Install

Purpose

A tank changeout is won or lost on the items that go invisible the moment the closet door shuts: the relief discharge, the expansion control, the vent draft, the gas leak check. The water connections announce their own failure within a day. Those four fail silently, months later, as a weeping T&P nobody reports, a cracked tank, or an appliance spilling flue gas into a hallway. This procedure forces a number or an observed state at each point before the unit is left running.

Scope

Covers a like-for-like residential changeout of a storage water heater, gas atmospheric or electric, in its existing location using the existing vent, gas drop and branch circuit. It ends at handover with the unit firing and the record filed.

It does NOT cover a fuel change, a move to a new location, a tankless conversion, or a vent that has to be resized: those are permitted work and a re-quote. Routine servicing of an existing unit belongs to the water heater annual service SOP.

Roles and the handoff

The handoff that actually breaks: the installer finds the closet 2 in short, phones the office, and the job is repriced verbally. Nothing lands in writing and the next tech inherits a mystery, so every stop rule below routes through the lead.

Procedure

1. Isolate the fuel and prove it dead before any fitting is loosened. Gas: close the appliance shutoff upstream of the union and tag it. Electric: open the breaker, then verify at the upper element terminals with a meter proved on a known live source before and after (NFPA 70E-2021, 120.5; the practice is 29 CFR 1910.333(b)(2), which governs electrical work rather than 1910.147). Acceptance: 0 V to ground and line to line. Wrong looks like 118 V off a mislabeled breaker: stop and find the real circuit.

2. Measure the site against the unit on the truck before you drain a drop. Closet width and height, connector diameter against the new draft hood collar, nipple centers, door swing. Acceptance: it fits with the connector able to rise at least 1/4 in per foot to the vent, no downward run. Wrong looks like a taller replacement forcing a flat connector: stop and call the lead, this is a re-quote.

3. Drain with the discharge routed and watched. Stored water at 120 to 140 F scalds through skin in seconds, so run the hose to grade and watch the discharge before opening the drain valve; crack an upstairs hot tap to break the vacuum. Acceptance: flow falls to nothing with that tap open. Wrong looks like a plastic drain valve blocking on sediment: do not force it, pull the T&P and siphon, and record the sediment, which predicts what this water does to the next tank.

4. Break the gas union downstream of the closed shutoff, cap the drop, then pull and read the vent connector. Gas trapped in the drop vents when the union opens, so no torch is lit in that room until step 9 passes its leak check, no flame is ever used to find a leak, and the door stays open. Acceptance: cap fitted with no odor at one minute, connector interior bright or lightly sooted, chimney clear at the thimble. Flaking rust or heat discoloration at the draft hood means the old unit was spilling: photograph it and route the vent to permitted inspection before setting the new unit.

5. Set the unit on a pan with the required restraints. A pan piped to an indirect waste is required where a leak would damage the structure (International Plumbing Code 504.7 as adopted by your jurisdiction, the Uniform Plumbing Code carrying the parallel requirement), and strapping at the upper and lower third applies where adopted, California Plumbing Code 507.2 being the version most shops meet. Acceptance: pan drain runs downhill to a legal termination. Wrong looks like a pan with no outlet, which is a bucket.

6. Make up the water connections with dielectric separation and lead-free materials. Solder, flux and fittings on the potable side must meet the 0.25 percent weighted-average lead limit for wetted surfaces set by the Safe Drinking Water Act as amended by the Reduction of Lead in Drinking Water Act of 2011. Soldering in a closet is hot work: ventilate, keep flux fume out of your breathing zone, shield the framing, extinguisher in reach, 30 minute fire watch. Acceptance: joints dry at 20 minutes.

7. Pipe the T&P discharge full size, downward, terminating unthreaded. No reduction, no valve, no trap, terminating 6 in to 24 in above the floor or pan bottom with a plain end so nobody can cap it, in material rated for 250 F. Acceptance: measured termination height inside that range, end plain. Wrong looks like a threaded stub with a cap, which turns a safety device into a pressure vessel. Never deferred to a later visit.

8. Set expansion control against a measured static pressure. Gauge static at a hose bib with nothing running. If the service carries a check valve, pressure reducing valve or backflow preventer, the system is closed and needs an expansion tank pre-charged to that static pressure, set with the tank isolated and empty of water. Acceptance: pre-charge within about 5 psi of measured static. Wrong looks like a tank left at factory pre-charge against much higher house pressure: it waterlogs on the first cycle and shows up months later as a T&P drip the next tech replaces instead of diagnoses.

9. Reconnect the gas with a sediment trap and leak check every disturbed joint. A sediment trap at the appliance connection is required by NFPA 54, the National Fuel Gas Code (ANSI Z223.1), in the edition your authority having jurisdiction has adopted. Check with a listed leak-detection solution or an electronic detector, never a flame. Acceptance: no bubble growth at any disturbed joint over 3 minutes. Wrong looks like a slow film lifting after a minute: take that joint apart and redo it.

10. Fill and purge fully before the burner is allowed to light. Firing gas into a part-empty tank destroys the glass lining and can crack the vessel, and an exposed electric element burns out in seconds. Open the cold supply with the highest hot fixture running. Acceptance: solid stream, no spitting, for 60 continuous seconds, then recheck every joint at full pressure. Wrong looks like intermittent spit: keep purging rather than energizing early.

11. Fire the unit and prove draft under worst-case house conditions. Clip a personal CO monitor at your breathing zone before the burner lights; the OSHA permissible exposure limit is 50 ppm as an 8 hour time weighted average (29 CFR 1910.1000 Table Z-1), so a climbing reading is a stop, not a note. With the closet door shut and the dryer plus every exhaust fan running, let it run 60 seconds and test the draft hood relief opening with smoke. Acceptance: smoke drawn in within a few seconds, monitor at background. Wrong looks like smoke still rolling out at 60 seconds: close the gas, red-tag, leave it off, call the lead.

12. Set delivered temperature and hand over deliberately. 120 F is the common default because it sharply cuts scald risk to children and older adults. Where the customer or a health authority requires hotter storage to manage Legionella growth, store hotter and fit a thermostatic mixing valve so fixtures still see about 120 F. Acceptance: measured temperature at the nearest fixture after a 10 minute recovery, within about 5 F of target. Show the customer both shutoffs and the T&P lever.

When the site does not match the quote

Wrong fuel or capacity on the truck: do not substitute a smaller tank to save the trip, because a recovery complaint becomes a warranty visit. Reschedule and record the correct model. No permit where the jurisdiction requires one for a changeout: many do, and an uninspected swap surfaces at the property sale, so the lead pulls it and the install schedules behind it. Customer declines a code item such as the pan drain or the straps: the T&P discharge is never declinable, and for anything else write the item, the date and the customer's own words into the record before you leave. A verbal decline that is not written down becomes your defect at the next inspection.

The record this produces

One changeout record filed on the customer's equipment record, found by address rather than by date:

• New model, serial, capacity, fuel and date, plus the removed unit's model and serial for the warranty claim
• Measured static pressure, expansion tank pre-charge as set, and whether the system was found closed
• T&P discharge termination height and material
• Sediment trap fitted yes or no, and the leak-check method
• Spillage result at 60 seconds with the house in worst case, and the CO monitor reading
• Delivered temperature at the nearest fixture and the thermostat setpoint
• Any declined item in the customer's words, and any red-tag with its reason
• Photos of the T&P termination, the expansion tank gauge, the connector rise, the finished closet

The office reads it to close the permit and register the warranty. The next tech reads it to learn whether the house is a closed system and what the water did to the last tank.

Worked pass: 50 gallon atmospheric gas swap

Existing unit: 50 gallon atmospheric gas, 11 years old, hall closet with a louvered door, venting into a masonry chimney it once shared with the furnace.

• Steps 1 to 2: gas closed and tagged; closet 24 in wide against a 22 in unit, 7 in height clear, 4 in connector against a 4 in collar. Pass.
• Step 3: drained in 22 minutes, heavy sediment noted. Pass with a note.
• Step 4: cap fitted, no odor at one minute; connector lightly sooted, chimney clear at the thimble. Pass.
• Steps 5 to 7: pan piped to the laundry standpipe, straps at upper and lower third, joints dry at 20 minutes, discharge terminated 9 in above the pan bottom with a plain 3/4 in end. Pass.
• Step 8: static 78 psi at the hose bib, PRV present so the system is closed. Tank read 40 psi from the factory and was set to 78 psi isolated and dry. Left at 40 against 78, the bladder sits fully compressed from the first cycle and the tank does nothing, which is the install that drips at month four.
• Steps 9 to 10: sediment trap fitted, three disturbed joints clean at 3 minutes, solid stream upstairs for 75 seconds. Pass.
• Step 11: FAILED. Burner lit with the monitor clipped at the collar. Door shut, dryer and range hood running, smoke at the relief opening rolled outward and was still rolling at 60 seconds; the monitor moved from background to 21 ppm in the hallway. Stop rule taken: gas closed, unit left off, red tag applied, lead called from the driveway, customer told in person that the heater is installed and will not be left running.

The cause was not the new heater. The furnace on that chimney had been replaced the previous winter with a sealed-combustion unit vented in PVC through the rim joist, leaving the water heater alone on a flue sized for two appliances. An oversized flue on one small appliance stays cold, never establishes draft, and spills at the hood. That is a permitted liner job, booked for the Thursday. The record carried the 60 second result, the 21 ppm reading, a photo of the abandoned thimble, and the customer's signature acknowledging the unit was left off.

References

• NFPA 54 / ANSI Z223.1, National Fuel Gas Code, in the edition your authority having jurisdiction has adopted, for sediment traps, appliance connection and venting
• ANSI Z21.10.1, the standard storage water heaters are certified to, which sets 400 ppm air-free carbon monoxide as the certification limit
• 29 CFR 1910.1000 Table Z-1 for the carbon monoxide exposure limit, and 29 CFR 1910.333(b)(2) for electrical work practice
• Safe Drinking Water Act as amended by the Reduction of Lead in Drinking Water Act of 2011, for the 0.25 percent wetted-surface lead limit
• See related: the water heater annual service SOP and the gas line pressure test SOP