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Craig Muccio

About "Ask the Energy Expert"

Craig Muccio runs FPL's Conservation Research & Development Program and crunches the numbers to figure out how you can save by managing your energy use.

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Water heaters: Turn off or leave on?

By Craig Muccio

Asked on: April 30, 2015 by Frank L., FPLblog.com comment

Is it a good idea to turn off the hot water tank overnight or when not using it?

We turn off lights and other things when we’re not using them. So, of course you’d wonder if you should do the same with your water heater. In fact, it was one of the top questions we received from customers following my recent post on the cost of heating water in your home. Because there was so much interest, we wanted to talk a little more about water heaters this month.

Savings from turning off water heater
Turning off your water heater when you don’t need it could help you save a few bucks each month if you have a tank-style heater that’s standard in many homes or even one of the newer hybrid, or heat pump, systems. That’s because even though water heaters are well insulated, a small amount of heat does escape the tank while hot water is waiting for you to use it. That energy loss is typically about 10 percent. So, for an average FPL customer which we estimate spends a little under $20 every month to heat water, about $2 of that cost is due to heat loss. That’s money that you could save by turning off your water heater when you’re not using it.

And, you may be wondering if you’ll end up using more energy to heat water that’s cool because you’ve turned off the heater. Not really. Think of it this way -- you’re paying to heat the water anyway, regardless of whether you heat it right before you use it or heat it and let it sit until your next use. The small cost savings comes from avoiding the escaped heat while it’s waiting for you to use it.

The “how to”
Want to give this a try, but don’t know how? My colleague shows you how to turn off your water heater in this Ask the Energy Expert video

If your water heater has an on/off disconnect switch as shown in the video, we recommend turning on the water heater a half hour before you need it, giving the unit time to heat your water. Then, you should shut it off again just before you start using hot water. Why? Well, if you wait until after a shower, for example, to turn off your water heater, it will start heating the new water that fills the tank, leaving you with another full tank of hot water and the escaped heat situation that you’re trying to avoid.

I imagine some of you might worry that you’d run out of hot water if you turned off your water heater before hopping in the shower. Keep in mind, your tank has a certain amount of hot water available at one time, and once it’s used, it takes time to reheat the tank as new water is added. So, essentially, you can run out of hot water regardless of whether you leave the water heater on during your shower or turn it off. Tankless water heaters are the only option that can supply hot water instantaneously.

What about timers?
Of course, you don’t need to turn off your water heater manually. You could always consider automating this step with a timer. This may save you some time, but possibly not the money you’re hoping for. You’ll need to weigh the cost of buying a timer and installing it against the estimated $2 monthly energy savings you could get from turning off your water heater manually.

More information
Have a water heater question I haven’t answered? I sincerely wish I could answer every question we get! Here are some additional resources that may help you find what you need:

 U.S. Department of Energy

FPL Energy Experts

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