Department of Energy

#AskEnergySaver: Home Water Heating

March 24, 2014

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Did you know: Water heaters account for nearly 17 percent of a home’s energy use, consuming more energy than all other household appliances combined. For more about water heaters, check out our <a href="/node/612476">Energy Saver 101 home water heating infographic</a>. | Photo by Eric Grigorian, U.S. Department of Energy Solar Decathlon.

Did you know: Water heaters account for nearly 17 percent of a home’s energy use, consuming more energy than all other household appliances combined. For more about water heaters, check out our Energy Saver 101 home water heating infographic. | Photo by Eric Grigorian, U.S. Department of Energy Solar Decathlon.

To help you save money by saving energy, we launched #AskEnergySaver -- an online series that gives you access to some of the Energy Department’s home energy efficiency experts. During 2014, experts from the Department and our National Labs will be answering your energy-saving questions and sharing their advice on ways to improve your home’s comfort.

Hot water has become essential to our daily lives -- from washing hands to cleaning dishes to showering -- and quickly adds up to higher energy bills. It comes as no surprise that water heaters account for nearly 17 percent of a home’s energy use, consuming more energy than all other household appliances combined. That’s why we asked you to share your water heating questions this month.

To answer them, we turned to Sam Rashkin, Chief Architect for the Energy Department’s Building Technologies Office. Through the Challenge Home program, Rashkin helps bridge the gap between federal research and the housing industry, working with homebuilders to use more energy-efficient technologies and building methods.

What is the cheapest/easiest thing you can do to reduce water heating bills (especially in older buildings)?
-- from @energycare on Twitter

Sam Rashkin: The cheapest thing you can do is change your behavior -- turn off the water when scrubbing dishes and while washing your hair in the shower. Another behavioral change that has a big impact is setting your water heater to vacation mode when you’re away for an extended time.

The next cheapest thing to do is make small upgrades, like wrapping your water heater with an insulation blanket if it isn’t currently insulated and installing low-flow fixtures in your sinks and showers.

A more expensive way to save hot water is to add a heat trap configuration to the hot water plumbing line exiting the heater -- this minimizes heat losses because hot water is more buoyant and continually flows up. Lastly, the most costly upgrade is to replace an old inefficient hot water heater with a new high-efficiency option. Options include high-efficiency gas storage tank and instantaneous water heaters, heat pump water heaters and solar water heaters.

What’s the best type of water heater?
Eric Hunt on Facebook asks: Is an on-demand hot water heater more energy efficient than a tank water heater?

SR: It sounds like you’re confusing an on-demand water heater with an instantaneous (or tankless) water heater. While they sound similar, a tankless water heater heats water in one pass (or instantly) without a tank and doesn’t have standby energy losses that are associated with storage water heaters. On-demand systems use a pump that is activated by sensors or controls to circulate hot water to a bathroom or kitchen “on demand.” This ensures minimal wasted water and can be installed on any water heater to help to improve its efficiency.

I believe you were asking about instantaneous hot water heaters, which are more efficient than storage tank water heaters. This is because they eliminate much of the energy use for keeping a tank fully heated (note: “much” is used because instantaneous systems now have a small electric heated tank to avoid what is called the “cold water sandwich” effect), and they are usually rated at higher operational efficiencies. It is important to keep in mind that tankless water heaters require a larger gas pipe size because they apply so much more heat for instantaneous heating, and this could add significantly to installation costs.

George Voll on Facebook asks: Is a hybrid heat pump water heater more efficient than an on-demand gas or electric water heater?

SR: It depends on a number of factors, including the amount of water used, frequency of use, and how electric and gas prices compare in your area. However, generally the heat pump water heaters that are more efficient have comparable efficiency to instantaneous gas water heaters and are much more energy efficient than instantaneous electric water heaters.

What actions can you take to ensure a tankless water heater is most efficient?
@ericwg on Twitter asks: How long do showers have to be for a tankless water heater to be less efficient?

SR: Shower length has no impact on the efficiency of a tankless water heater. With that said, it is important to keep in mind that the longer the shower, the more hot water consumed, and the higher the hot water heating bill.

@k8_sabbe on Twitter asks: At what temperature is my tankless water heater most energy efficient?

SR: Generally, the most efficient water heater temperature is the lowest temperature to provide the necessary hot water. For most homes, that is 120 degrees F because dishwashers now have built-in heating boosters to raise the temperature to the necessary 145 degrees F for sterilizing dishes. Sinks only need 105 degrees F hot water for cleaning hands -- localized tankless heaters below individual sinks should be set to that temperature.

#AskEnergySaver is there a more affordable alternative to solar panels when it comes to using renewable energy for heating water?
-- from @arulprakash94 on Twitter

SR: Solar thermal water heating (using heat from the sun to warm water) is the most cost- and energy-efficient renewable energy alternative for water heating. This is because renewable electric systems, like solar electric and onsite wind power, have substantial energy loss when converting electricity to heat. With solar thermal water heating, there are a multitude of options, and the best choice for you will depend on your local climate and architectural factors.

I have been heating my home and water with an oil burning furnace. Both need to be replaced. How do I get help with these when I don't know anything about my options and which brands would work best for my home?
-- from norwichumom via email

SR: The ENERGY STAR products website is the best source for finding information on energy-efficient water heaters and other replacement options for your oil furnace.