Water Heater Installation Kit
The heater is the thing you shopped for. These are the four parts the inspector, the warranty and the ceiling below actually care about.
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For a standard 50-gallon replacement, buy four parts. An Amtrol Therm-X-Trol ST-12 expansion tank (4.4 gallon volume, 3.2 gallon acceptance, 11 in x 15 in) if the house is on a closed system. A Camco 20841 22-inch aluminium drain pan. A HoldRite QS-50 strap kit in a seismic jurisdiction — it carries California DSA approval #97-010. And a Honeywell AM-1 mixing valve if you want to store hot and deliver safe.
Nobody sells a genuine, complete water heater installation kit, because the right contents depend on your plumbing, your jurisdiction and where the tank sits. What the big-box "installation kit" boxes contain is usually two flexible connectors and a pair of dielectric unions — the easy parts. These are the four that get missed, and three of the four are code items somewhere in the country.
The four parts, side by side
| Part | Key specification | Why it is on the list |
|---|---|---|
| Amtrol Therm-X-Trol ST-12 | 4.4 gal volume, 3.2 gal acceptance, 11 in dia x 15 in H, 3/4 in NPTM, 150 psig max, 50 psig factory pre-charge | IPC 607.3 requires thermal expansion control on a closed system, and says the relief valve may not do the job |
| Camco 20841 aluminium pan | 22 in inside diameter, 2-1/4 in deep, PVC drain fitting | A 50-gallon tank will eventually leak; the pan decides whether that is a mop or a ceiling |
| HoldRite QS-50 Quick Strap kit | Up to 80 gal, 24 gauge galvanised steel, 38 in straps, 4 straps + 4 lag bolts + 4 J-clips, California DSA approval #97-010 | Seismic restraint is mandatory in California and several other jurisdictions, and the approval number goes on the permit |
| Honeywell AM-1 (AM101) mixing valve | 3/4 in lead-free brass, 150 psi, 212°F, adjustable 70 - 145°F depending on variant | Lets you store at 140°F for bacteria control and deliver at a safe tap temperature |
Quick picks
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| # | Product | Best for | Price |
|---|---|---|---|
| 1 |  Amtrol Therm-X-Trol ST-12The size most 50-gallon installs actually need: 4.4 gallons of volume and 3.2 gallons of acceptance, which is what Amtrol's chart calls for at 60 psi static pressure. | 50 gallon tanks at normal pressure | Check price on Amazon No live price feed on this site, so we show none. #ad |
| 2 |  Camco 20841 aluminum pan, 22 inThe 22-inch aluminum pan: the right size under a standard 50-gallon tank, which is itself usually 22 inches in diameter. | 50 gallon tanks | Check price on Amazon No live price feed on this site, so we show none. #ad |
| 3 |  HoldRite QS-50 Quick Strap kitThe strap kit inspectors recognize: 24-gauge galvanized steel for tanks up to 80 gallons, with California Division of the State Architect approval number 97-010. | Seismic zones, code compliance | Check price on Amazon No live price feed on this site, so we show none. #ad |
| 4 | Honeywell AM-1 (AM101) mixing valveThe thermostatic mixing valve that lets you store water at 140°F for bacteria control and still deliver a safe temperature at the tap — adjustable from 70 to 145°F depending on variant. | Storing hot, delivering safe | Check price on Amazon No live price feed on this site, so we show none. #ad |
The four parts in full
Pick 1 — 50 gallon tanks at normal pressure
Amtrol Therm-X-Trol ST-12
The size most 50-gallon installs actually need: 4.4 gallons of volume and 3.2 gallons of acceptance, which is what Amtrol's chart calls for at 60 psi static pressure.
| Tank volume | 4.4 gallons |
|---|---|
| Maximum acceptance volume | 3.2 gallons |
| Diameter | 11 in |
| Height | 15 in |
| System connection | 3/4 in NPTM |
| Maximum working pressure | 150 psig |
| Maximum operating temperature | 200°F |
| Factory pre-charge | 50 psig |
What is good
- 3.2 gallons of acceptance covers 50-gallon heaters at the static pressures most municipal supplies actually run
- Same 3/4 in NPTM connection and 150 psig rating as the ST-5
- Headroom means a slightly wrong pre-charge still works
- The size a plumber would fit by default
What is not
- 11 inches across and 15 inches tall needs real clearance above the heater
- Too heavy to hang unsupported from a horizontal tee
- Overkill for a 30- or 40-gallon tank on low pressure
Skip it if: Skip it if there is under 16 inches of clear space above your cold inlet. People buy the ST-12, find it will not fit, and then install it unsupported — which is how a tee cracks a year later.
No live price feed on this site, so we show none. #ad
Specifications above from Amtrol ST-12 sizing chart sheet (PDF); Amtrol Therm-X-Trol brochure, September 2025 (PDF). We have not tested this unit ourselves.
Pick 2 — 50 gallon tanks
Camco 20841 aluminum pan, 22 in
The 22-inch aluminum pan: the right size under a standard 50-gallon tank, which is itself usually 22 inches in diameter.
| Inside diameter | 22 in |
|---|---|
| Depth | 2.25 in |
| Material | Aluminum |
| Drain fitting | PVC |
What is good
- Matches the 22-inch diameter of the common 50-gallon tank with room for the fitting
- Aluminum construction
- Standard PVC drain connection
- Fits the alcove a 50-gallon tank already occupies
What is not
- A 22 in pan under a 22 in tank is a tight fit — check the drain boss clears
- 2.25 in depth
- Requires a gravity drain path
Skip it if: Skip it for a heat pump water heater. Those are usually wider than a resistance tank of the same capacity and also produce condensate continuously, which means a larger pan and a committed drain, not a shallow pan.
No live price feed on this site, so we show none. #ad
Specifications above from Pacific Plumbing listing, Camco 20841; HD Supply listing, Camco 22 in ID pan. We have not tested this unit ourselves.
Pick 3 — Seismic zones, code compliance
HoldRite QS-50 Quick Strap kit
The strap kit inspectors recognize: 24-gauge galvanized steel for tanks up to 80 gallons, with California Division of the State Architect approval number 97-010.
| Capacity | Water heaters up to 80 US gallons |
|---|---|
| Material | 24 gauge cold-rolled steel, galvanized |
| Strap length | 38 in |
| Kit contents | 4 straps, 4 lag bolts, 4 J-clips, 2 x 3/8 in carriage bolts, 2 x 3/8 in hex nuts |
| Approval | California DSA approval #97-010 |
What is good
- Named approval number is what an inspector in a seismic jurisdiction wants to see
- Complete kit: nothing to source separately at the hardware store
- Covers every residential tank size up to 80 gallons
- Galvanized steel will not rot off the wall in a damp garage
What is not
- Lag bolts need real studs or blocking, not drywall anchors
- Steel straps are harder to route around a tight alcove than a soft belt
- Over-tightening a steel strap can dent a tank jacket
Skip it if: Skip the rigid steel kit if the tank sits in a corner you cannot reach around. The soft-belt version exists for exactly that install, and a strap you cannot tension properly is decoration.
No live price feed on this site, so we show none. #ad
Specifications above from Supply House listing, HoldRite QS-50 galvanized strap; RWC BIM data, QS-50 water heater restraint. We have not tested this unit ourselves.
Pick 4 — Storing hot, delivering safe
Honeywell AM-1 (AM101) mixing valve
The thermostatic mixing valve that lets you store water at 140°F for bacteria control and still deliver a safe temperature at the tap — adjustable from 70 to 145°F depending on variant.
| Size | 3/4 in |
|---|---|
| Body | Brass, lead free |
| Pressure rating | 150 psi |
| Temperature rating | 212°F |
| Adjustable range | 70 - 145°F (variant dependent; 70 - 120°F and 70 - 180°F variants exist) |
| Connections | NPT, union CPVC, union press or PEX depending on variant |
What is good
- Lets you raise the tank set point for Legionella control without scalding anyone
- Also increases usable hot water: hotter storage mixed down goes further
- Multiple connection styles so it suits copper, CPVC, PEX or press
- Anti-scald and anti-chill in one device
What is not
- Several variants share the AM101 prefix with different temperature ranges — order the right one
- It is one more device on the hot outlet that can fail closed
- Needs a union or isolation to be serviceable
Skip it if: Skip it if you are not going to raise the tank temperature. Fitted to a tank set at 120°F it does almost nothing, and it adds a restriction and a failure point for no benefit.
No live price feed on this site, so we show none. #ad
Specifications above from First Supply listing, Honeywell AM101-UCPVC-1LF/U; Granite Group listing, AM101-UP-1LF/U, 70-145F. We have not tested this unit ourselves.
Which of these you actually need
- Expansion tank — only on a closed system. If cold water reaches the heater through a check valve, pressure-reducing valve or backflow preventer, you need one. Most modern houses have a PRV. Expansion tank code requirements has the code text, and expansion tank sizing explains why static pressure, not tank gallons, drives the size.
- Drain pan — any time there is something below worth protecting. Buy it by inside diameter: 20 inches for most 30 and 40 gallon tanks, 22 inches for a 50, 26 inches for an 80 or a heat pump model. The drain fitting has to go somewhere, or the pan just holds two gallons and overflows.
- Seismic straps — wherever the jurisdiction says so. Two straps, upper and lower third, four inches clear of the controls, mechanically fixed to studs. Water heater earthquake strap requirements quotes the statute.
- Mixing valve — if you store above 120°F. Storing at 140°F suppresses bacterial growth; delivering at 140°F scalds. The valve is how you have both.
What else goes on the van
- Flexible connectors and dielectric unions. Genuinely useful, genuinely cheap, and usually what is in the box labelled installation kit.
- A T&P discharge pipe run to within a few inches of the floor or outside, in a material rated for the temperature. Never capped, never valved.
- Pipe dope or PTFE tape rated for potable water.
- A leak detector. The pan tells you nothing; a sensor in the pan tells you at 2am. Best water heater leak detectors.
- A new anode rod, if the heater is going somewhere awkward to service later. Water heater anode rods.
Buy by job type
| Job | Buy | Skip |
|---|---|---|
| 50-gallon tank, basement, closed system | ST-12 expansion tank + 22 in pan | Straps, unless your jurisdiction requires them |
| Tank in an upstairs closet | Pan + leak detector + expansion tank | Nothing — this is the install where everything earns its place |
| California or another seismic jurisdiction | HoldRite QS-50 strap kit | Nothing; the approval number goes on the permit |
| Household with young children or elderly residents | Honeywell AM-1 mixing valve | Nothing — store hot, deliver safe |
| 80-gallon or heat pump model | 26 in pan instead of 22 | The 22 in pan; it will not fit |
| Open system, slab floor, floor drain alongside | Pan only | The expansion tank, if the system is genuinely open |
If you are doing the work yourself rather than buying parts for a plumber, read can I replace my own water heater? first — the permit question decides more of this than the parts list does.
What goes in with it
A water heater is a system, not a box. These are the parts that go in with it, and the ones people discover they need halfway through the job.
- Expansion tank
Required by code on a closed system, which is most homes with a pressure-reducing valve.
- Drain pan
Cheap insurance anywhere the tank sits above something you care about.
- Anode rod
The part that decides when the tank leaks. Replacing it is the highest-value hour of maintenance there is.