Hot Water Heaters Indirect Vs. Direct

A hot water heater provides the hot water you use throughout your home.

Direct Heaters

Your home's water heater provides the hot water that comes from the tapYour home's water heater provides the hot water that comes from the tap
There are many different types of hot water heating systems, including conventional storage water, or direct heaters, tankless coil, and indirect water heaters, along with less common systems such as demand water heaters, heat pump water heaters and even solar water heaters. Both direct and indirect hot water heaters can run on a variety of fuels, and each type has advantages and disadvantages.

Direct heaters store anywhere from 20 to 80 gallons of hot water in a storage reservoir. Hot water comes from the top of the tank to your tap. A cold water line at the bottom of the tank constantly fills the tank, replenishing the hot water that comes off the top. Depending on the type of fuel the heater uses, some form of burner, valve, or heating element connected to one or more thermostats, warms the cold water entering the tank.

Indirect Heaters

Indirect water heaters also require a storage tank, but use your home's furnace or boiler to heat fluid pushed through a coiled pipe called a heat exchanger, which runs through that storage tank. The water tank stores energy and allows the furnace to turn off and on less often, saving energy. The combination of an indirect water heater, a high-efficiency boiler and a well-insulated tank can be the least expensive means of heating water.

Heat Loss

Both direct and indirect heaters constantly heat the water in the tank even when a hot water tap isn't running. This heating results in an energy cost called standby heat loss. Only tankless water heaters such as demand, or tankless coil, systems avoid standby heat loss entirely. Heavily insulated tanks can significantly reduce it and lower annual operating costs. The Department of Energy recommends tanks with a thermal resistance, or R-Value, of R-12 to R-25.

Installation & Care

Correct installation and regular maintenance of your water heater can optimize its energy efficiency. It's best to contact qualified plumbing and heating contractors for installation. They will consider fuel type, climate, building code requirement, and safety issues when installing your heater.

Both indirect and direct water heaters benefit from regular maintenance. Maintenance tasks for indirect systems vary depending on the manufacturer. Most direct heaters can benefit from common maintenance tasks such as flushing a quart of water from the tank every three months, and checking temperature and pressure every six months. Your direct water heater's anode rod should be inspected every three to four years.

Fuel Types & Energy Efficiency

Both indirect and direct systems can use gas, oil, propane and electricity. When choosing a water heater, you should consider the energy factor, or EF, listed among its specifications. EF is a measurement of a heater's energy efficiency, based on daily usage, and accounts for recovery efficiency, standby loss and cycling loss. Be careful to include fuel cost when making your decision. A higher EF system using a more expensive fuel will cost more to run.

About the Author

Steve Lacher has been a skilled technical consultant since 1994. He has written training materials and articles for technical journals such as "Domino Power Magazine," taught on television, been a developer and performed many other tasks related to the use of technology in business. Lacher holds a Bachelor of Arts in writing seminars from the Johns Hopkins University.