Phoenix Summer Heat and Your Water Heater: Days Over 100 Degrees Across the Valley

A water heater in a Phoenix garage spends about a third of the year in air hotter than 100 degrees. This page shows how many days a year reach 100 or higher at 11 official weather stations across the Valley, using NOAA's 30 year climate normals, which are the current official set as of 2026, and what that heat does to the equipment.

Most Valley water heaters sit in a garage, an attic or an outdoor closet, none of which is cooled. For three to four months the air around the tank runs well above 100 degrees, which ages the relief valve, the anode, plastic fittings and the control board faster than the same unit would age in a milder climate. Add very hard water and the working life of a tank here is usually shorter than the number printed on the box.

Water mains and the service line to your house are buried shallow in ground that bakes all summer, and pipes that run through an attic can sit in air well above 130 degrees. None of the Valley water providers we checked publish a tap water temperature, so we do not print one. If you want your own number, run the cold tap for two minutes in July and put a kitchen thermometer in a glass.

Yes. A tankless unit is rated by how many gallons per minute it can raise by a given number of degrees. When incoming water is warm, the unit has less work to do and can supply more fixtures at once. When it is cold in January, the same unit supplies fewer. We size for the winter condition so you are not short of hot water in the one season you want it most.

The thermostat setting is about safety at the tap, not the room the heater sits in. 120 degrees is the usual recommendation. What heat does change is maintenance: check the relief valve and the expansion tank yearly, flush sediment yearly, and look at any attic unit's drain pan and drain line before summer, since a leak up there does the most damage.

They are official U.S. Climate Normals from NOAA's National Centers for Environmental Information, which average each station's daily records over the 30 years from 1991 to 2020. Days at or above 100 degrees is NOAA's own published figure for each station, not something we computed. NOAA updates the normals once a decade, so the 1991 to 2020 set is the current official one as of 2026 and will stay so until the 2001 to 2030 set is released. Recent summers have run hotter than the 30 year average.