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Old 12-03-2009, 02:21 PM   #29 (permalink)
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It depends a lot on the ambient temp of the house or closet where the heater is located.

The original poster asked if flipping off the breaker in the morning, then resetting it in the evening will save power.... the answer is absolutely YES.

The reason is simply that heat exchange is not linear to the difference of heat. If the water heater is 60 degrees warmer than the house (60* house, 110* water heater), it is losing heat FASTER than if it is only 20 or 30 degrees warmer than the house. So the heater will likely cycle during the day to keep the hot water hot enough.

If turned off, the heater will radiate heat and get cooler... but it cools more slowly as it gets closer to ambient temps. When you turn it back on, nearly 100% of the heat that is produced by the element goes into the water.

The question becomes: is the heat lost during the day enough to bother flipping the breaker? Since flipping the breaker is essentially zero-cost... it makes sense to do it. Unless the extra breaker cycles shorten the life of the breaker. That could negate savings.

If you wake up more than 1/2 hour before your shower(s), the best thing to do might be turn off the heater all day and all night, just turning it on 30-60 minutes before you shower, then turning it right off after the showers.

Or just get an instant-on hot water heater (tankless) and be done.

Originally Posted by fshagan View Post
Electric water heaters are insulated pretty well, so you probably won't save much by turning it off. 100% of the energy goes into the water as heat (or very nearly so), so the only losses you can save are "standby losses" from heat radiating out of the jacket. Because electric water heaters don't have a flue that tends to cool the water, they usually retain the heat very well.

If you turn it off after it is hot, leave it off for 8 hours and turn it back on, does the element have to come on to heat the water again? If it does, spend your money on insulating the tank, the pipes coming out of the tank, installing a "thermal trap" in the outlet pipe, etc. If the water in the tank is still above room temperature then you haven't lost all of the heat and you won't save much energy by waiting until you come home to turn the elements back on. The intermittent use of the elements during the day will come very, very close to the longer run you need when you turn the elements back on.
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