Know your fuel, your space, and your hot water demand before you shop. Pick the type your home can support, size it by first-hour rating or flow rate, and check what the install needs: gas line, venting, electrical, or a condensate drain. Then compare efficiency, rebate rules, and warranty, and plan for the permit.
Which type of water heater fits your home?
The type that fits is usually the one your home already supports: the fuel you have, the vent you have, and the space around the heater. Switching types can work well, but it often adds gas, venting, or electrical work.
| Type | How it heats | Best fit | What it needs |
|---|---|---|---|
| Gas tank | Burner under a storage tank | Homes with gas and an existing flue | Gas line, vent, combustion air |
| Electric tank | Elements inside the tank | Homes without gas | 240 V circuit |
| Gas tankless | Burner heats water as it flows | Busy homes with gas that want endless hot water | Larger gas line, dedicated venting |
| Electric tankless | Elements heat water as it flows | One sink, a casita, or a small home | Very large electrical capacity |
| Hybrid (heat pump) | Pulls heat from the air, with backup elements | Electric homes with a garage | Air space, 240 V or 120 V model, condensate drain |
| Point-of-use | Small unit at one fixture | A far sink or a restaurant hand sink | Space under the sink, power |
Each type has its own page. See gas vs electric water heaters, what a hybrid water heater is, whether electric tankless works in Arizona, and what a point-of-use water heater is. For solar, see whether solar water heaters are worth it in Arizona.
### Can you switch fuel types?
You can, but plan for the work. Gas to electric means capping the gas line and adding a heavy electrical circuit. Electric to gas means running a gas line and a vent. Even gas to gas needs care. A.O. Smith's manual says to "Make sure the gas supplied is the same type listed on the model rating plate," since natural gas and propane models are built differently. See natural gas vs propane at home.
How big a water heater do you need?
Size by how much hot water you use in your busiest hour, not by the number on the tank. ENERGY STAR explains that a heater's output "is determined measured by two things: The capacity or volume (in gallons) and the first-hour rating." It defines the first-hour rating as how much hot water "the unit can deliver during a busy hour under standard test conditions."
Its practical advice for a replacement is simple: "If your current water heater meets your needs most of the time, you can probably replace it with one the same size." Find your current tank's size on "the nameplate or yellow Energy Guide sticker." ENERGY STAR adds that a higher first-hour rating means "you can get better hot water performance without having to buy a larger capacity water heater."
For tankless models, size by flow rate instead. Add up the gallons per minute of the fixtures you run at the same time, then check the unit's flow at the temperature rise your water needs. Our page on what size water heater you need walks through both methods, and what to look for in a 50 gallon gas water heater shows the specs on a real model.
What will the installation need?
The install needs depend on the type, and they often decide the choice. Check these before you order:
- Gas supply. A higher-input burner may need a bigger gas line. A.O. Smith's manual says "A gas line of sufficient size must be run to the water heater," and calls for "A readily accessible manual shut-off valve in the gas supply line serving the water heater."
- Venting. An atmospheric tank uses a vertical flue. Power vent and direct vent models vent through a wall or roof. Changing vent types means new wall or roof work.
- Electrical. Electric tanks and most hybrids need a 240 V circuit. ENERGY STAR notes that hybrid models running on a standard 120-volt outlet "are now available in many markets." Whole-house electric tankless units can need a service upgrade.
- Space and air. Measure height, width, and clearances. Hybrids are taller and need room air around them. ENERGY STAR says they should have "1,000 cubic feet of air space around the water heater."
- Drainage. Hybrids and condensing gas models make condensate, which needs a drain.
### What does Phoenix code require with a new water heater?
The plumbing code Phoenix uses says water heaters "shall be installed in accordance with the manufacturer's instructions," and adds safety parts that ride along with every storage heater:
- 1A relief valve. Section 504.4 requires a "self-closing (levered) pressure relief valve and temperature relief valve or combination thereof."
- 2A pan where a leak would cause damage. Section 504.7 requires one where "water leakage from the tank will cause damage."
- 3Thermal expansion control. Under Section 607.3, a thermal expansion device is required when the cold supply passes through a check valve, pressure reducing valve, or backflow preventer.
Garage installs also have to meet the 18 inch rule for garage water heaters, and tanks need seismic strapping. See whether you need a permit to replace a water heater in Phoenix, and check water heater clearance and access code for the space rules.
How should you compare efficiency, rebates, and warranty?
Compare efficiency by the Uniform Energy Factor (UEF) on the spec sheet, where higher is better. ENERGY STAR says its certified gas storage models "Use about 10 percent less energy compared to standard gas water heaters." For electric homes, it says a certified heat pump water heater "can save a family of four an estimated $550 a year on their energy bill" compared with standard electric resistance. That figure is ENERGY STAR's national estimate, not a local quote.
Rebates come with rules, so read them before you buy. SRP's heat pump water heater rebate terms, for example, require a unit with a UEF of 2.8 or better, an application "within six months of the installation date," and "a dated copy of the paid invoice." They also say "Rebates are not available for new construction." ENERGY STAR advises: "Be sure to review the eligibility rules before you make your purchase."
Warranty terms vary by model line, often by several years within one brand. Compare the tank warranty and the parts warranty separately.
### How do you choose who installs it?
ENERGY STAR's buying guide lists what to ask for when choosing a contractor:
- "Request cost estimates in writing."
- "Ask for references."
- "Check the company with your local Better Business Bureau."
- "See if the company will obtain a local permit if necessary and understands local residential building codes and other regulations."
When is the best time to buy a water heater?
The best time is before the old one fails. ENERGY STAR puts it this way: "plan ahead for your next water heater replacement and you will have time to research and select the best technology for your situation before it's an emergency." It adds that "Your installer may need time to order the proper model, and it may take longer to install than a standard water heater."
Signs that it's time to plan include rust-colored hot water, a leak at the tank, rumbling from sediment, and hot water that runs out sooner than it used to. Our pages on whether to repair or replace a water heater, a water heater leaking from the bottom, and how to check for a water heater recall cover those.
HQ Plumbing & Air sizes, installs, and replaces tank, tankless, hybrid, and point-of-use water heaters across the Phoenix area, licensed and insured, with free estimates and upfront pricing. See our water heater service.
Know your fuel, your busiest hour, and your install needs. The right heater follows from those three. Mesa gas customers can also check Mesa's gas appliance rebate for water heaters.