Gas and Electric water heaters
In homes, gas water heaters are the most common type of water heating system, and most models hold 30 to 75 gallons. Hot water is release from the top of the tank, while cold water enters the bottom of the tank so the tank is always full. In addition to natural gas, water heaters may be fueled by propane or fuel oil.
Natural gas and propane water heaters.
A gas burner under the tank heats the water. When water temperature falls, a thermostat opens the gas valve. When the water reaches a predetermined temperature the valve closes.
Electric water heaters. Like gas-powered conventional storage water heaters most electric water heaters have a reservoir from 6 to 75 gallons. An electric water heater usually had two electric elements, each with its own thermostat. The element at the bottom of the tank maintains a minimum thermostat setting. The upper demand element provides hot water recovery.
Whether powered by gas or electricity, conventional storage water heaters have become more efficient over the years but they are still less efficient than a tankless water heater because water is constantly being heated in the tank. Standby heat loss occurs and energy is wasted even when a hot water tap isn’t running.