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Water heater insulation, a bad job (C) Daniel FriedmanWater Heater Standby Losses
Reduce stand-by energy heat loss in hot water heaters

This article discusses water heater or calorifier or geyser standby losses.

This discussion is part of a series of articles on how to improve the hot water pressure, quantity, flow, and water temperature safety in a building.

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How to Reduce Standby Losses in Water Heaters

Water heater timer control (C) Daniel FriedmanWater heater standby loss is defined as the amount of heat that is lost by a water heater when it is not in use or is in "standby" mode.

A water heater with comparatively high standby losses will be more-expensive to operate than one with lower standby losses, thus the cost of hot water used by building occupants will be higher when standby losses are higher.

Average [water heater] standby load for existing homes was found to be 1200 kWh/year, or approximately 26% of total energy consumed for water heating. (Pratt 1993).

A number of designs and features have been explored to reduce calorifier standby losses:

Question: is it better to turn the water heater on and off to safe electricity?

2018/12/24 EG said:

I have older model AO Smith electric water heater in this apartment I moved into. Is it better to keep the power turn on or turn it on and off to conserve electricity?

This Q&A were posted originally at AO SMITH WATER HEATER AGE & MANUALS

Reply:

EG

You can turn off the water heater when leaving for several days or longer, and will save a little money - standby losses from modern electric water heaters are not so great that turning the heater off for a few hours saves you much money..

Conventional wisdom is that one can reduce the cost of electric hot water, if you use hot water at fairly regularly times, by having have an electrician install an automatic timer that turns the heater off for periods when it will not be in use -

see TIMERS for ELECTRIC WATER HEATERS

Interestingly, Elk and Auberg, in an un-dated report, found that timers don't save much energy, but that where hot water use occurs at regular times, turning the heater down (or maybe off) after the last daily use can save money. Here is an excerpt:

It is apparent that for no-flow standby loss reduction, the use of a clock-timer is marginal at best.

A more appropriate test sequence would be one which represents a typical household water use pattern, allowing the tank to be de-energized prior to the final hot water use during the day.

Under idealized conditions, the upper limit of savings achievable with a clock-timer would be to reduce standby losses to zero for the duration of the "off" time by completely using the last tankful of heated water.

A more realistic limit would be to use the last tankful down to about 100°F which would reduce the temperature differential to about 30 degrees over ambient the off period.

Other interesting facts about standby losses of water heaters:

Gas water heaters have higher standby losses than electric water heaters as additional heat from the water tank is lost through the exhaust flue (an automagic flue damper can reduce that loss)

Larger water heater tanks, because of their larger surface area, tend to have higher standby losses.

Tankless water heaters that do not maintain any reservoir of hot water have zero standby losses.

Research on Water Heater Standby Loss Costs & Reduction


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