The water heater, by the numbers

Water heating "accounts for about 18% of your home's energy use," the Department of Energy says (DOE Energy Saver, archived copy of 31 May 2026). The four pages on this shelf put local numbers on that share: what a tank costs to run on Clarksville's utilities, what a heat pump model saves, how hot the water should be, and how to keep sediment out of an electric tank.

Running cost: electric or gas

The running cost page starts from the federal test that rates every new heater: 55 gallons of hot water a day, warmed 67°F (10 CFR 430, Appendix E). A 50-gallon tank at the federal efficiency floor then needs about 3,528 kWh if electric or 197 therms if gas. The page prices both on CDE Lightband, Cumberland Electric Membership Corporation (CEMC) and Clarksville Gas & Water (CGW) rates, and shows how far CGW's monthly commodity charge moved over the past year.

Heat pump water heaters and the TVA offer

The heat pump page covers the $900 TVA EnergyRight discount at participating retailers (TVA EnergyRight) and reprices ENERGY STAR's national savings at local rates. It also explains where such a unit can go, since it draws its heat from a roomy space kept between 40°F and 90°F.

Temperature and scald risk

The temperature page sets out why 120°F is DOE's default, how quickly hotter water burns (CPSC), and the cases where a higher tank setting with mixing valves at the taps makes sense. It walks through checking the tap with a thermometer and the maker's thermostat steps, with the breaker off whenever a panel is open.

Flushing and the relief valve

The flushing page follows the electric manual's ten steps, with power off from the first step until the tank is full (electric water heater manual). It also covers the yearly test of the temperature and pressure relief valve. On gas heaters, every page on this shelf stops at the water side; gas controls, pilots and burners are work for a licensed plumber.