Before you begin. This procedure is general reference information, not professional advice. Equipment varies by manufacturer, model, and year. Always follow the documentation supplied with your equipment — where it differs from this page, follow the manufacturer. Verify that you have the tools, the working conditions, and the ability to do this task safely. If anything is unclear, if the equipment is damaged, or if the task exceeds your experience, stop and use a qualified professional. You are responsible for your own safety and for the outcome. This site accepts no liability for any loss, damage, or injury arising from the use of this information.
Specifications marked unverified could not be traced to a manufacturer source. Do not rely on them — obtain the value from your equipment documentation.
Summary
A water heater carries more information than most owners ever read. Beyond the model number and the serial number, the same rating plate — or a second yellow label next to it — lists the tank capacity, the first hour rating or the recovery rate, the input rating, the voltage or the gas type, the maximum working pressure, and the minimum clearance to combustible material. Every other page on this site about your water heater assumes you can find these numbers, and this page is where you find them and write them down.
This page does not decode a serial number into a date of manufacture. That is a separate task with its own manufacturer-specific rules, and the record on finding the age of a water heater covers it in full. Use that page once you have the serial number written down here.
This page also will not print a generic number for your maximum working pressure, your minimum gas pressure, your voltage, or any other safety-critical figure, because that number belongs to your specific model. Only your own rating plate or your manufacturer's documentation can give it correctly. What this page teaches is which field to look for and where manufacturers put it, grounded in Rheem's and AO Smith's own installation manuals. Read the actual figure from your own plate, write it down, and take it to a professional when you need work done.
Safety
DO NOT TOUCH THE GAS VALVE OR THE VENT PIPE ON A WORKING WATER HEATER.
These parts get hot and can burn your hand.
Necessary equipment
| Item | Note |
|---|---|
| Flashlight | The print on a rating plate is small and the space is often dark. |
| Camera or phone | Use this to make a photograph of the rating plate. |
| Pen and paper | Use these to record each field from the rating plate. |
| Dry cloth optional | Use this to clean dust from the rating plate. |
Find the rating plate
Estimated 2 min to 4 min
DO NOT MOVE A FULL WATER HEATER TO READ THE PLATE.
A full water heater is very heavy and can crush your foot.
- Find the rating plate on the water heater.2mReport a problem with step 1, Find the rating plate
- The rating plate is a label on the outer tank of the water heater.
- Bradford White states that the plate carries the model number and the serial number.
- A gas water heater usually has the plate near the gas valve.
DO NOT USE A WET CLOTH ON THE PLATE.
Water can make the print hard to read.
- Clean dust from the rating plate with a dry cloth.<1mReport a problem with step 2, Find the rating plate
- Point a flashlight at the rating plate from one side.<1mReport a problem with step 3, Find the rating plate
- Light from one side makes the stamped print easy to read.
- Light from the front causes a reflection.
Record the model number and the serial number
Estimated 3 min to 5 min
No tier-1 source was found for this value. Take it from the documentation supplied with your equipment.
- Write the brand name from the rating plate.<1mReport a problem with step 1, Record the model number and the serial number
- The brand on the plate can differ from the brand on the box.
- Write the model number from the rating plate.<1mReport a problem with step 2, Record the model number and the serial number
- Copy each character exactly as it appears.
- Write the serial number from the rating plate.1mReport a problem with step 3, Record the model number and the serial number
- Copy each character exactly.
- The letter O and the number zero are easy to confuse.
- The letter I and the number one are also easy to confuse.
- See the other page for the steps to find a date.
DO NOT HOLD THE CAMERA TOO CLOSE TO THE PLATE.
A reflection from the flash can hide the numbers.
- Make a photograph of the whole rating plate.<1mReport a problem with step 4, Record the model number and the serial number
Record the capacity and the hot water output
Estimated 2 min to 3 min
Source: Understanding Your 2023 Water Heater EnergyGuide Label · tier 1 · accessed 2026-08-03
Source: Understanding Your 2023 Water Heater EnergyGuide Label · tier 1 · accessed 2026-08-03
No tier-1 source was found for this value. Take it from the documentation supplied with your equipment.
No tier-1 source was found for this value. Take it from the documentation supplied with your equipment.
- Write the tank capacity from the rating plate or the energy label.<1mReport a problem with step 1, Record the capacity and the hot water output
- Rheem calls this value the tank size or the rated capacity.
- The capacity can also appear only on the energy label.
- Write the first hour rating or the recovery rate from the plate or the label.<1mReport a problem with step 2, Record the capacity and the hot water output
- Rheem defines this value as the hot water a full tank can give in one hour.
- A tankless water heater can show a flow rate instead.
Record the power supply data
Estimated 2 min to 3 min
Source: Residential Super High Efficiency Water Heater Use & Care Manual (AP21831 Rev 02) · tier 1 · accessed 2026-08-03
Source: Electric Residential Hybrid Water Heater Use & Care Manual (AP23657 Rev 04) · tier 1 · accessed 2026-08-03
No tier-1 source was found for this value. Take it from the documentation supplied with your equipment.
No tier-1 source was found for this value. Take it from the documentation supplied with your equipment.
No tier-1 source was found for this value. Take it from the documentation supplied with your equipment.
No tier-1 source was found for this value. Take it from the documentation supplied with your equipment.
No tier-1 source was found for this value. Take it from the documentation supplied with your equipment.
- If the water heater is a gas model, write the gas type from the rating plate.<1mReport a problem with step 1, Record the power supply data
- The type is natural gas or propane gas.
- AO Smith states that the gas type must match the data plate.
- If the water heater is a gas model, write the minimum gas pressure from the rating plate.<1mReport a problem with step 2, Record the power supply data
- Rheem prints this pressure on the rating plate.
- Rheem uses this pressure to adjust the burner.
- If the water heater is an electric model, write the voltage from the rating plate.<1mReport a problem with step 3, Record the power supply data
- Rheem prints the required voltage on the rating plate.
- If the water heater is an electric model, write the wattage from the rating plate.<1mReport a problem with step 4, Record the power supply data
- Some manufacturers name this value the element wattage.
- Write the input rating from the rating plate.<1mReport a problem with step 5, Record the power supply data
- A gas water heater usually shows this value in BTU per hour.
- The input rating for a gas water heater can change at high altitude.
Record the pressure limit and the clearance
Estimated 1 min to 2 min
Source: Residential Standard Gas Water Heater Installation Instructions and Use & Care Guide (document 100263112, January 2015) · tier 1 · accessed 2026-08-03
No tier-1 source was found for this value. Take it from the documentation supplied with your equipment.
No tier-1 source was found for this value. Take it from the documentation supplied with your equipment.
- Write the maximum working pressure from the rating plate.<1mReport a problem with step 1, Record the pressure limit and the clearance
- Rheem uses this value to set the relief valve limit.
- Write the minimum clearance to combustible material from the rating plate.<1mReport a problem with step 2, Record the pressure limit and the clearance
- AO Smith uses this clearance to protect nearby material from heat.
After the job
Estimated 1 min
- Keep your written record and your photograph with your home records.<1mReport a problem with step 1, After the job
- An insurer, a plumber, or an electrician can ask for this record.
- Give this record to a professional before you buy a part or a replacement.<1mReport a problem with step 2, After the job
Terminology
This page uses one term for each item and holds it throughout, as ASD-STE100 requires. Equipment sellers and other guides use the names below for the same parts.
- water heater
- Also called: hot water heater, hot water tank, hot water cylinder, boiler, geyser, immersion heater
- rating plate
- Also called: data plate, nameplate, name plate, spec plate, specification label, serial number sticker, model number tag
- first hour rating
- Also called: FHR, first-hour rating, hot water output, how much hot water can my water heater make
- tank capacity
- Also called: gallon capacity, tank size, rated capacity, how many gallons is my water heater
- input rating
- Also called: BTU rating, BTU per hour, wattage rating, heating capacity
- maximum working pressure
- Also called: max working pressure, working pressure rating, tank pressure rating
- energy label
- Also called: EnergyGuide label, yellow tag, yellow energy sticker, efficiency label
When to use a professional
This page reads a label. It does not open, adjust, or repair anything on the water heater.
Speak to a qualified plumber or a qualified electrician before you order a part. Give this person the numbers you wrote down. A qualified plumber or a qualified electrician must choose the numbers that fit your repair.
Stop if you do not see the rating plate from eye level. A qualified plumber can read the plate during a service visit.
Speak to a qualified plumber if the tank shows rust, or if you find water below the water heater. An old tank that leaks does not become safe again.
Give a professional your written record and your photograph. This record saves the professional a second visit to read the same plate.
Common questions
What is the rating plate on a water heater?
It is the manufacturer's own label, usually a metal or vinyl sticker on the outer tank, and it carries the facts that identify your exact unit: the brand, the model number, the serial number, the capacity, and the ratings that describe how it heats and holds water. Rheem calls it a rating plate. AO Smith calls the same kind of label a data plate. Whatever the name, it sits near the top of a storage tank or on the front of a tankless unit, and it is the single most useful sticker on the appliance.
What do all the numbers on my water heater actually mean?
Most storage water heaters print a gallon capacity, a first hour rating or a recovery rate, an input rating, and either a voltage and a wattage or a gas type and a minimum gas pressure. Storage tanks also mark a maximum working pressure and, on gas models, a minimum clearance to anything that can burn. This page walks through each field and tells you where manufacturers typically put it, but it will not hand you a made-up number for your specific model. Read the real figure off your own plate and write it down.
Where do I find the gallon capacity and the first hour rating?
Rheem's own consumer guide to the EnergyGuide label defines tank size as the actual amount of water the tank contains, and it defines the first hour rating as the hot water your water heater can supply in one hour starting from a full tank. Both figures often appear on the bright yellow EnergyGuide sticker as well as on the rating plate itself. A tankless water heater has no tank to fill, so it lists a flow rate instead of these two figures.
Is the rating plate the same sticker as the serial number label?
On almost every water heater, yes — one label carries the model number, the serial number, and the other fields this page covers. This page teaches you to read the whole label. If you only need to turn the serial number into a date of manufacture, the separate record on finding the age of a water heater covers that one task in full, because the decoding rules differ by manufacturer.
Can I use the numbers from the plate to order a part or plan a repair myself?
Write the numbers down and bring them to a qualified plumber or a qualified electrician. The plate tells you what your specific unit needs, but a professional still has to match that to the correct part, confirm your local code, and judge the condition of the tank before any repair or replacement goes ahead. A number copied correctly from a good plate is still only the starting point for that conversation.
Why won't this page just give me a typical pressure or voltage number?
Because a typical number is exactly the kind of guess this site refuses to publish. Maximum working pressure, minimum gas pressure, and voltage all vary by model and by brand, and a plausible-sounding figure that happens to be wrong is worse than no figure at all. Rheem's and AO Smith's own manuals confirm that each of these values is printed on the individual unit's own rating plate for that reason. Read the number that belongs to your water heater, not a number that sounds about right for water heaters in general.
Related procedures
- How to find and record the model and serial number of every appliance in the house
- How old is my water heater and how do I read the serial number
- Where is the water under my hot water heater coming from, and does it mean I need a new one?
- How do I insulate the hot water pipes at my water heater
- How to flush a water heater
- How do I check if my water heater's pressure relief valve pipe is installed correctly
- How to read the label on a power tool and understand what the numbers mean
- How do I decode the date code on my appliance and find out how old it is
Sources
Every specification on this page is traced to one of these sources. Tier 1 is a manufacturer document, a published standard, or a government safety authority. See Standards for the full tiering rule.
- Tier 1My Water Heater - warranty, age and serial number location
- Tier 1Residential Super High Efficiency Water Heater Use & Care Manual (AP21831 Rev 02)
- Tier 1Electric Residential Hybrid Water Heater Use & Care Manual (AP23657 Rev 04)
- Tier 1Residential Standard Gas Water Heater Installation Instructions and Use & Care Guide (document 100263112, January 2015)
- Tier 1Understanding Your 2023 Water Heater EnergyGuide Label
Revision history
Current version 1 · updated 2026-08-03 · next review due 2027-08-03
- v1 · 2026-08-03First draft. Covers every field a reader can expect on a residential water heater's rating plate (called a data plate by AO Smith): brand, model number, serial number, tank capacity, first hour rating or recovery rate, input rating, gas type and minimum gas pressure or voltage and wattage, maximum working pressure, and minimum clearance to combustible material. Grounded in three manufacturer use and care manuals newly registered for this record (a Rheem gas model, a Rheem hybrid electric model, and an AO Smith gas model) plus Rheem's own EnergyGuide label explainer for the plain-language definitions of tank size and first hour rating, and the already-registered Bradford White plate-location source. No safety-critical figure (pressure, voltage, clearance) is asserted as a general value for any brand or model; every such field publishes as an instruction to read it from the reader's own plate, per rule 1. The date-of-manufacture field is deliberately routed to the existing find-the-age-of-a-water-heater record rather than repeated, per the backlog note that the two pages overlap at the serial number. No step opens, moves, drains, or disconnects anything.
Corrections to this page are listed in the public corrections log. Reports that are credible and not yet verified are listed in the public errata register, and an open one renders above the step it concerns.
Comments and corrections
Found an error? A correction with a manufacturer source is applied and logged publicly. You can also write to corrections@fixchecklist.com.
Every step above carries its own report control, which tags the report with that step so a correction reaches the right place. For anything about the procedure as a whole — the order of the sections, a step that is missing, something that did not match your equipment — use this: report something about this whole procedure.