The rating plate is how you identify your water heater. Every unit has one. It tells you the model, manufacture date, capacity, efficiency, and electrical requirements.
What is a rating plate?
A rating plate (also called a data plate, nameplate, or rating label) is a permanently attached metal plate or adhesive label on every water heater that displays the unit's specifications, certifications, and regulatory information. It is required by federal law (10 CFR Part 430) and safety standards (UL/CSA).
Where to find it
Gas Tank
Side of the tank near the bottom, above the burner access panel. Often visible without moving the unit.
Electric Tank
Side of the tank, typically near the upper thermostat access panel. May be behind insulation panels on some models.
Tankless
Front panel or side of the unit. On indoor models, it is usually visible after removing the front cover. On outdoor models, it is on the exterior casing.
Heat Pump
Side of the tank or on the heat pump compressor housing at the top of the unit. Some models have two labels: one for the tank and one for the heat pump system.
What each field means
| Field | What it tells you |
|---|---|
| Model, Model No., Mod. | Manufacturer's model number identifying the exact product line, capacity, fuel type, and feature set. This is the most important field for finding a replacement. Model numbers encode specifications. For example, A.O. Smith model GNRH50 100 indicates Gas, Natural, Residential, High-efficiency, 50-gallon, 100 series. |
| Serial, Serial No., S/N | Unique identifier for that specific unit. Encodes the manufacturing date on most brands. Required for warranty claims and parts orders. Serial number formats vary by manufacturer. See the brand_serial_number_decoding section for how to extract the manufacture date. |
| MFG Date, Date of Manufacture, Date MFG | The date the unit was manufactured. Some brands print this explicitly; others encode it in the serial number. Not all brands print a separate manufacture date. Rheem typically does; others require serial number decoding. |
| Rated Storage Volume, Capacity, Tank Size, Nominal Capacity | The volume of hot water the tank holds, in U.S. gallons. Tankless units do not have this field. The actual usable hot water is measured by First Hour Rating (FHR), not tank capacity. A 50-gallon tank may deliver 60-80 gallons in the first hour. |
| Input, BTU Input, Rated Input, Input Rating | The energy input rate. Measured in BTU/h for gas units and kilowatts (kW) for electric units. Higher input means faster recovery. Gas units typically range from 30,000 to 199,000 BTU/h for residential models. Electric tank units are commonly 4.5 kW per element. |
| UEF, Uniform Energy Factor | The federally mandated efficiency rating. Higher UEF means lower operating cost. Replaced the older Energy Factor (EF) metric in 2017. UEF values are tested under one of four draw patterns (very small, low, medium, high) depending on the unit's first hour rating or GPM. Units with UEF values that meet ENERGY STAR thresholds earn the certification. |
| First Hour Rating, FHR, 1st Hour Rating, First Hr. Rating | The number of gallons of hot water a storage tank unit can deliver in the first hour of use, starting with a full tank of hot water. This is the primary sizing metric for tank water heaters. Applies only to storage tank water heaters. Tankless units use GPM (gallons per minute) instead. |
| GPM, Flow Rate, Max GPM, Gallons Per Minute | Maximum flow rate in gallons per minute. The primary performance metric for tankless water heaters. GPM ratings are tested at a specific temperature rise (typically 35 or 77 degrees F). Real-world GPM depends on incoming water temperature. |
| Max. Working Pressure, Maximum Pressure, Working Pressure | The maximum water pressure the tank is designed to handle safely, measured in PSI (pounds per square inch). Most residential water heaters are rated for 150 PSI. If your home's water pressure exceeds 80 PSI, a pressure-reducing valve is recommended. |
| T&P Valve Rating, Temperature and Pressure Relief, Relief Valve | The temperature and pressure at which the safety relief valve will open. Required by code on all tank water heaters. The T&P valve is a critical safety device. It opens if water temperature exceeds 210 degrees F or pressure exceeds 150 PSI to prevent tank rupture. |
| ENERGY STAR, ES | The EPA ENERGY STAR certification mark, present if the unit meets or exceeds efficiency thresholds set by the EPA. ENERGY STAR certified water heaters may qualify for utility rebates and state incentives. The federal 25C tax credit expired December 31, 2025. |
| Manufacturer, MFG by, Manufactured by | The manufacturer's legal name and address. Required by federal labeling law. Some brands are manufactured by the same parent company. A.O. Smith also manufactures State, American, and other private-label brands. Bradford White does not sell through retail channels. |
| UL Listed, CSA Certified, UL/CSA, cULus | The safety certification mark from an accredited testing laboratory. UL (Underwriters Laboratories) and CSA (Canadian Standards Association) are the most common. Building codes require water heaters to bear a listing mark from an accredited lab. A unit without this mark cannot legally be installed in most jurisdictions. |
| AHRI Ref, AHRI Certified Ref No., AHRI No. | The AHRI (Air-Conditioning, Heating, and Refrigeration Institute) certified reference number. Used to look up independently verified performance data. AHRI certification verifies that the manufacturer's efficiency claims have been independently tested. The number can be looked up at ahridirectory.org. |
| Estimated Yearly Energy Cost, Est. Annual Operating Cost | The FTC-required estimated annual operating cost based on national average energy prices and the DOE test procedure. This figure appears on the yellow EnergyGuide label, which is a separate label from the rating plate but often located nearby. It uses standardized energy prices that may not match your local rates. |
| Recovery, Recovery Rate, Recovery GPH | The number of gallons per hour the unit can heat from inlet temperature to the thermostat setpoint. Indicates how quickly hot water replenishes after use. Gas units recover significantly faster than electric (typically 40+ GPH vs. 20 GPH for comparable tank sizes). |
Additional fields by water heater type
Beyond the common fields, each type of water heater carries extra information on its rating plate. Open the type you have.
Gas-fired water heaters
Additional fields found on gas-fired water heaters (natural gas and propane/LP).
| Field | What it tells you |
|---|---|
| Gas Type, Fuel, For Use With | The type of gas the unit is designed to burn: Natural Gas or Liquid Propane (LP). Units are factory-configured for one type. Using the wrong gas type is extremely dangerous. Natural gas and LP operate at different pressures and require different orifice sizes. Never convert a unit without a manufacturer-approved conversion kit. |
| BTU Input, Input Rating BTU/h, Burner Input | The burner's heat input rate in BTU per hour. Residential gas tank units typically range from 30,000 to 50,000 BTU/h. High-efficiency condensing units may have higher inputs (up to 100,000 BTU/h). Tankless gas units range from 120,000 to 199,000 BTU/h. |
| Manifold Pressure, Gas Pressure, Inlet Pressure | The gas pressure at the burner manifold, measured in inches of water column (in. W.C.). Manifold pressure is critical for proper combustion. Incorrect pressure causes incomplete burning, sooting, or dangerous carbon monoxide production. |
| Ignition, Ignition Type, Pilot Type | How the burner is ignited. Modern units use electronic ignition (no standing pilot) for better efficiency. Standing pilot models are increasingly rare in new production. |
| Vent Type, Venting, Vent Category | The venting category determines what type of vent pipe and installation method is required. Venting type must match the replacement unit. Switching from atmospheric to power vent (or vice versa) requires significant installation changes. |
| NOx, Ultra Low NOx, SCAQMD Compliant | Nitrogen oxide emission rating. Ultra Low NOx units are required in certain jurisdictions, notably SCAQMD (South Coast Air Quality Management District) in Southern California. If the existing unit is Ultra Low NOx, the replacement must also be Ultra Low NOx in regulated jurisdictions. |
Electric resistance water heaters
Additional fields found on electric resistance water heaters.
| Field | What it tells you |
|---|---|
| Voltage, Volts, V | The required electrical supply voltage. Most residential electric water heaters require 240V. The electrical circuit must match the voltage, amperage, and wire gauge on the rating plate. |
| Wattage, Watts, W, Total Watts | The power consumption of the heating elements in watts. Standard residential units use 4500W elements. Some compact or low-draw models use 1500W or 2000W elements. |
| Amps, Amperage, A, Full Load Amps | The current draw in amperes. Determines the required circuit breaker size and wire gauge. A standard 4500W / 240V element draws 18.75 amps. NEC requires a 30-amp breaker and 10-gauge wire for this load. |
| Phase, Ph | The electrical phase: single-phase for residential, three-phase for commercial. Residential units are single-phase. Three-phase is commercial only. |
| Hz, Frequency, Hertz | The electrical frequency. 60 Hz in North America. |
| Elements, Heating Elements, Upper/Lower Element | The number and configuration of heating elements. Most residential tank units have dual elements that alternate (non-simultaneous) operation. The upper element heats first for faster recovery at the top of the tank. |
| Min. Wire Size, Wire Gauge, AWG | The minimum wire gauge required for safe installation, per NEC standards. Must match or exceed the rating plate specification. Using undersized wire is a fire hazard. |
Heat pump / hybrid water heaters
Additional fields found on heat pump water heaters (hybrid units).
| Field | What it tells you |
|---|---|
| Refrigerant, Refrigerant Type, Ref. | The type of refrigerant used in the heat pump compressor. R-134a is being phased down under the AIM Act. Newer units may use R-410A or R-744 (CO2). Refrigerant type matters for servicing. |
| Charge, Refrigerant Charge, Factory Charge | The amount of refrigerant factory-charged into the heat pump system. Only EPA Section 608 certified technicians may handle refrigerants. The charge amount is needed for service and leak repairs. |
| Compressor, Compressor Type | The type of compressor in the heat pump. Most residential HPWHs use rotary compressors. Compressor type affects noise levels and serviceability. |
| Operating Modes, Modes | Available operating modes for the heat pump system. Heat Pump Only mode is most efficient but slowest recovery. Hybrid mode uses resistance elements for high-demand periods. |
| Ambient Temp Range, Operating Range | The ambient air temperature range in which the heat pump can operate effectively. Below the minimum ambient temperature, the unit falls back to electric resistance heating. This is critical for installation location planning. |
Tankless water heaters
Additional fields found on tankless (on-demand) water heaters.
| Field | What it tells you |
|---|---|
| Flow Rate Range, GPM Range, Min/Max Flow | The minimum and maximum flow rates the unit can handle. Below the minimum flow rate, the unit will not activate. This minimum activation rate matters for low-flow fixtures. |
| Temp Rise, Temperature Rise, Delta T | The temperature increase the unit can achieve at various flow rates. Higher temperature rise means lower flow rate. The rated GPM on the EnergyGuide is typically at 77 degrees F rise. Real-world performance depends on incoming water temperature. |
| Min. Activation Flow, Minimum Flow Rate | The minimum water flow required to activate the burner or heating element. If water flow drops below this threshold, the unit shuts off. Low-flow faucets and fixtures may not always trigger activation. |
| Min. Gas Line, Gas Supply Line Size | The minimum gas supply line diameter required. Tankless gas units require larger gas lines than tank units due to higher BTU input. Upgrading from a tank to tankless may require a gas line upgrade. |
Serial number date decoders by brand
Most manufacturers encode the manufacture date in the serial number. Use these to determine how old your water heater is.
A.O. Smith
Also applies to: State, American, Whirlpool (A.O. Smith manufactured), Reliance
Current (2008+)
First two digits are the 2-digit year, next two digits are the week of manufacture. Remaining digits are a production sequence number.
Example:
YYWW######First two digits are the 2-digit year, next two digits are the week of manufacture. Remaining digits are a production sequence number.
Example:
1604123456 → Year 2016, Week 04 (late January 2016)
Older numeric (1990s-2000s)
First two digits are the month (01-12), next two digits are the 2-digit year.
Example:
MMYY#######First two digits are the month (01-12), next two digits are the 2-digit year.
Example:
0399A123456 → March 1999
Letter-month prefix
A single letter represents the month (A=Jan, B=Feb, C=Mar, D=Apr, E=May, F=Jun, G=Jul, H=Aug, J=Sep, K=Oct, L=Nov, M=Dec; letter I is skipped). Followed by 2-digit year.
Example:
[Letter]YY#######A single letter represents the month (A=Jan, B=Feb, C=Mar, D=Apr, E=May, F=Jun, G=Jul, H=Aug, J=Sep, K=Oct, L=Nov, M=Dec; letter I is skipped). Followed by 2-digit year.
Example:
B01A123456 → February 2001- Serial number is on the rating plate label on the side of the tank near the bottom.
- Skip any leading letter prefixes (factory codes) and look for the first digits.
- When in doubt, call A.O. Smith at 800-527-1953 with the full serial number.
Bradford White
All years (rotating 20-year letter cycle)
First character is a letter representing the year (20-year cycle). Second character is a letter representing the month. Remaining digits are a sequential production number (7 digits before December 2007, 8 digits after).
Example:
[Year Letter][Month Letter]#######First character is a letter representing the year (20-year cycle). Second character is a letter representing the month. Remaining digits are a sequential production number (7 digits before December 2007, 8 digits after).
Example:
MF1234567 → M = 1995 or 2015, F = June. Use the ANSI compliance date on the label to determine which 20-year cycle.- Letters I, O, and Q are not used (to avoid confusion with 1, 0, and 2).
- To distinguish between the two possible years in the 20-year cycle, check the ANSI standards date also printed on the rating plate.
- Bradford White offers a serial number lookup tool at bradfordwhite.com/my-water-heater.
Rheem
Also applies to: Ruud, Richmond, GE (Rheem manufactured)
Current (10-digit format)
After any letter prefixes (R, RN, RNG, RHNG, etc.), the first two digits are the month (01-12) and the next two digits are the 2-digit year. The fifth character is a plant code. Remaining digits are a sequential production number.
Example:
[Prefix]MMYY[Plant]#####After any letter prefixes (R, RN, RNG, RHNG, etc.), the first two digits are the month (01-12) and the next two digits are the 2-digit year. The fifth character is a plant code. Remaining digits are a sequential production number.
Example:
R 0884B10488 → Month 08 (August), Year 84 (1984). Plant code B.- Strip any letter prefixes (R, RN, RNG, RHNG) before decoding.
- Many Rheem units also print the manufacture date explicitly on the rating plate as 'MFG. DATE', so check for that first.
- Rheem, Ruud, and Richmond use the same serial number format (same parent company).
Rinnai
2009 and later (letter-based)
First letter is the year. Second character represents the month. Remaining digits are production sequence.
Example:
[Year Letter][Month Code]########First letter is the year. Second character represents the month. Remaining digits are production sequence.
Example:
NK12345678 → N = 2021, K = October. Manufactured October 2021.
Before 2009 (numeric)
First two digits are the 2-digit year. Next two digits are the month (01-12).
Example:
YYMM########First two digits are the 2-digit year. Next two digits are the month (01-12).
Example:
06074363 → Year 06 (2006), Month 07 (July). Manufactured July 2006.- Letters I, O, and U are skipped in the year and month codes to avoid confusion with numbers.
- Serial number is on the rating plate on the front of the unit (behind the front cover on indoor models).
Navien
Current format
After a 5-character model code, the next 2 digits are the year, followed by 1 character for the month (1-9 for Jan-Sep, X=Oct, Y=Nov, Z=Dec), then 2 digits for the day of manufacture.
Example:
[Model Code 5 chars]YYMD#########After a 5-character model code, the next 2 digits are the year, followed by 1 character for the month (1-9 for Jan-Sep, X=Oct, Y=Nov, Z=Dec), then 2 digits for the day of manufacture.
Example:
ABCDE14X17001234 → 14 = 2014, X = October, 17 = 17th day. Manufactured October 17, 2014.- Navien offers a serial number lookup tool at navieninc.com/serial.
- The serial number sticker is on the side of the unit body.
- Older Navien serials may use a different format. Use the online tool for older units.
Noritz
All years
First four digits are the full 4-digit year. Fifth and sixth digits are the month (01-12). Remaining digits are a production sequence number.
Example:
YYYYMM########First four digits are the full 4-digit year. Fifth and sixth digits are the month (01-12). Remaining digits are a production sequence number.
Example:
200606123456 → Year 2006, Month 06 (June). Manufactured June 2006.- Noritz uses a straightforward 4-digit year format, making it one of the easiest brands to decode.
- Serial number is at the bottom of the data plate on the unit.
Takagi
2010 and later
First two digits are the month (01-12), next two digits are the 2-digit year.
Example:
MMYY########First two digits are the month (01-12), next two digits are the 2-digit year.
Example:
0318XXXXXXXX → Month 03 (March), Year 18 (2018). Manufactured March 2018.
Before 2010
Takagi units manufactured before 2010 (before the acquisition by Noritz's North American operations) do not encode the manufacture date in the serial number.
No date encodingTakagi units manufactured before 2010 (before the acquisition by Noritz's North American operations) do not encode the manufacture date in the serial number.
- Takagi was acquired by A.O. Smith in 2023. Newer units may follow A.O. Smith serial number conventions in the future.
- Pre-2010 units require calling customer service for exact manufacture date.
Using your rating plate to plan a replacement
How to use the rating plate to find a replacement water heater and prepare for installation. Match these fields in priority order when choosing a replacement.
| Field to match | Why it matters |
|---|---|
| Fuel Type | Must match existing fuel supply. Switching fuel type (gas to electric or vice versa) requires significant utility and infrastructure changes. |
| Venting Type | Must match existing vent configuration unless you are willing to pay for vent modifications. Atmospheric, power vent, and direct vent are not interchangeable without significant work. |
| Voltage Amperage | Electric units must match the existing electrical circuit. A unit requiring 240V/30A cannot run on a 120V/15A circuit without an electrician. |
| Capacity Or Gpm | Match or exceed the existing unit's capacity (gallons) or flow rate (GPM for tankless). Downsizing may leave you short on hot water. |
| Physical Dimensions | Height and width determine if the replacement fits the existing space. Measure the available space, not just the old unit. |
| Uef Rating | Federal minimum efficiency standards have increased over time. Your replacement will likely have a higher UEF than the old unit, which may qualify you for rebates. |
| Gas Type | Natural gas and propane units are NOT interchangeable without a conversion kit. Using the wrong gas type is extremely dangerous. |
How to photograph your rating plate
Tips for photographing the rating plate so a plumber or retailer can identify the right replacement.
- Clean the label with a damp cloth first. Rating plates collect dust, grease, and condensation that obscure the text.
- Use your phone's flashlight or a separate light source. Rating plates are often in dark, cramped spaces.
- Take the photo straight-on, not at an angle. Avoid glare from the flash reflecting off metal or laminated labels.
- Get close enough that all text is readable when you zoom in. Take multiple photos if the label wraps around.
- Photograph both the rating plate AND the yellow EnergyGuide label if present.
- If the label is too damaged to read, photograph the model number and serial number from any other labels on the unit (shipping labels, box stickers, manual cover).
- Text the photos to your plumber before the appointment so they can source the right replacement in advance.
What to tell your plumber or retailer
- Fuel type (gas or electric)
- Gas type if applicable (natural gas or propane)
- Venting type (atmospheric, power vent, or direct vent)
- Tank capacity in gallons (or GPM for tankless)
- Model number and serial number
- Physical dimensions of the installation space
- Any code requirements specific to your jurisdiction (Ultra Low NOx in Southern California, etc.)
Once you know what you have, you can size your replacement, compare heat pump models, check rebates in your state, estimate replacement cost.
What to do next
- Write down the model number and serial number from your rating plate.
- Search the model number in the search bar above to find your unit's full specs.
- If your unit has died, check the replacement page for compatible options with projected savings.
- If you need parts, use the serial number for warranty claims and the model number for parts orders.
Common questions
What is a water heater rating plate?
A rating plate (also called a data plate, nameplate, or rating label) is a permanently attached metal plate or adhesive label on every water heater that displays the unit's specifications, certifications, and regulatory information. It is required by federal law (10 CFR Part 430) and safety standards (UL/CSA).
Where is the rating plate located on my water heater?
It depends on the type. On tank water heaters it is a label on the side of the tank, near the burner access panel on gas units or the upper thermostat panel on electric units. On tankless units it is on the front or side panel, and on heat pump units it is on the side of the tank or the compressor housing at the top. The location guide above covers each type.
How do I tell how old my water heater is?
Most manufacturers encode the manufacture date in the serial number. Find your brand in the serial number decoders above and match your serial number to the format to read the month and year it was built.
What information is on the rating plate?
The plate lists the model number, serial number, tank capacity, input or wattage rating, efficiency (UEF), and the electrical or gas requirements. The field-by-field breakdown above explains what each one means.
What should I photograph to find a replacement or brief a plumber?
Photograph the rating plate straight-on with good light so the model and serial numbers are readable, plus the yellow EnergyGuide label if present. The replacement section above lists exactly what to capture and what to tell your plumber.
Related
Sources. Manufacturer documentation, 10 CFR Part 430, UL/CSA certification standards. Methodology