What should I look for in a 50 gallon gas water heater?

The first-hour rating is how much hot water a heater can supply in one busy hour, starting with a full tank. ENERGY STAR explains that a model's hot water output "is determined measured by two things: The capacity or volume (in gallons) and the first-hour rating." It adds that "The first-hour rating measures how much hot water the unit can deliver during a busy hour under standard test conditions."

That's why it matters more than the tank size. A heater with a stronger burner refills faster, so it delivers more in that first hour. ENERGY STAR's point: "you can get better hot water performance without having to buy a larger capacity water heater."

Here is what those numbers look like on one real 50 gallon model, A.O. Smith's ProLine GCR-50:

Notice that the "50 gallon" tank actually holds 48 gallons, and it delivers 84 gallons in the first hour because the burner keeps heating while you use it. Compare first-hour ratings across the models you're considering. If your household runs showers back to back in the morning, a higher first-hour rating is what you're paying for.

### Is 50 gallons the right size for you?

Start with what you have now. ENERGY STAR's advice is that "If your current water heater meets your needs most of the time, you can probably replace it with one the same size." You can find your current tank's capacity "by looking at the nameplate or yellow Energy Guide sticker." Size up when the house has changed. ENERGY STAR's heat pump buying guide suggests a larger unit if you "have added or are planning to add more occupants to your household or a new shower, faucet, dishwasher or washer that will be in frequent use." Our page on what size water heater you need walks through the math.

### Does a bigger burner need a bigger gas line?

It can. A higher BTU input burns more gas, and the pipe has to carry it. A.O. Smith's manual says "A gas line of sufficient size must be run to the water heater," and points installers to the National Fuel Gas Code and the gas supplier "concerning pipe size." If you move from a 40,000 BTU heater to a higher-input model, have the gas line checked before the new heater goes in. The same manual also calls for "A readily accessible manual shut-off valve in the gas supply line serving the water heater" and a sediment trap ahead of the gas control.

Look at the UEF, listed on the model's spec sheet. Higher is better. The GCR-50, a standard atmospheric model, is rated at 0.62. ENERGY STAR certified gas storage heaters use "better insulation, heat traps, and more efficient combustion systems," and ENERGY STAR's gas water heater fact sheet says they "Use about 10 percent less energy compared to standard gas water heaters."

Before you pick a higher-efficiency model, check how it vents, since that can change the install.

Your home needs the vent type that matches its existing setup, or a planned change to it. There are three common types:

Matching the vent type you already have keeps a replacement simple. A different vent type can mean new wall or roof work, and A.O. Smith's manual has specific instructions "For all side wall terminated, horizontally vented power vent, direct vent and power direct vent gas fueled water heaters." Changing the vent type is a bigger job, so price it before you choose.

Check the gas type, the fit, and the parts that protect the tank and the home.

• Gas type. A.O. Smith's manual says to "Make sure the gas supplied is the same type listed on the model rating plate." Natural gas and propane models are not interchangeable.
• FVIR design. State Water Heaters' handbook says "Most gas water heaters today have Flammable Vapor Ignition Resistant (FVIR) designs," built to reduce the chance that fumes in the room are ignited by the burner. A.O. Smith still warns that gasoline and other flammables "should never be stored or used in the same vicinity," naming garages as an example.
• Fit. Measure height, diameter, and clearances. The GCR-50 is 57 inches tall and 22 inches across, and its vent connection sits on top. Our page on water heater clearance and access code covers the space rules.
• Anode rod. The anode protects the tank from corrosion. A.O. Smith's manual says each heater has "at least one anode rod" and gives steps to remove and replace it. The GCR-50 uses a stainless steel CoreGard anode.
• Warranty. Warranty terms differ by model line. The GCR-50 carries a 6 year limited tank and parts warranty. Compare the tank and parts terms side by side.

Phoenix requires the same safety parts on every new storage water heater, whatever the brand. The plumbing code Phoenix uses says water heaters "shall be installed in accordance with the manufacturer's instructions," and adds these rules:

1. 1A relief valve. Section 504.4 requires a "self-closing (levered) pressure relief valve and temperature relief valve or combination thereof."
2. 2A pan where a leak would cause damage. Section 504.7 requires one when a storage tank sits "where water leakage from the tank will cause damage." Our page on water heater drain pan overflow explains how the pan works.
3. 3Thermal expansion control. Under Section 607.3, if the cold water supply passes through a check valve, pressure reducing valve, or backflow preventer, a thermal expansion device has to be installed on the cold supply.

For a garage install, also check the 18 inch rule for garage water heaters and seismic strapping. And see whether you need a permit to replace a water heater in Phoenix.

HQ Plumbing & Air installs and replaces gas water heaters across the Phoenix area, licensed and insured, with free estimates and upfront pricing. See our water heater service.

Compare first-hour ratings, match the vent and the gas, and let the code items ride along with the install.