More efficient to reheat water or keep it at constant temp.?

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Discussion Overview

The discussion revolves around the energy efficiency of reheating water versus maintaining it at a constant temperature in a kitchen water heater. Participants explore the implications of insulation, ambient temperature, and heating efficiency over time.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant suggests that the rate of heat loss is proportional to the temperature difference between the water and the room, implying that reheating might be more efficient.
  • Another participant expresses that if the tank is well insulated, the efficiency of reheating versus maintaining temperature may not matter.
  • Concerns are raised about the efficiency of the heating process, particularly if the reheat process is less efficient than maintaining heat.
  • Some participants note that if the water heater and central heating systems operate with the same efficiency, it may not impact energy consumption significantly.
  • One participant introduces a scenario where external conditions, such as high outdoor temperatures and air conditioning, could influence energy efficiency considerations.

Areas of Agreement / Disagreement

Participants express differing views on whether maintaining a constant temperature or reheating is more energy efficient, with no clear consensus reached. Some agree that insulation plays a critical role, while others introduce additional variables that complicate the discussion.

Contextual Notes

Participants acknowledge the lack of specific information about the insulation of the heater and the efficiency ratings of the heating systems involved, which may affect the conclusions drawn.

Who May Find This Useful

Individuals interested in energy efficiency, home heating systems, or those considering the operational costs of water heaters may find this discussion relevant.

safro
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A relatively simple question from a physics ignoramus:

I have a kitchen water heater with a 4 liter capacity. I can opt to reheat the water to 195 degrees F every time I want hot water (roughly every 2 hours over the course of the day) or I can keep the water constantly at 195 degrees. Which option is more energy efficient?

Some pertinent information:
The temperature of the room where I keep the water heater is 65 degrees F. Unfortunately I don't have a measure of the insulation of the heater.

My own intuition from some barely recalled high school physics: energy input is the same in either case.
 
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The rate of heat loss is proportional to the difference in temperature between water and the room. From that standpoint it would be better to reheat the water. This could be offset if for some reason the reheat process was less efficient than the maintain heat process, but I'm not sure if that could happen.
 
safro said:
A relatively simple question from a physics ignoramus:

I have a kitchen water heater with a 4 liter capacity. I can opt to reheat the water to 195 degrees F every time I want hot water (roughly every 2 hours over the course of the day) or I can keep the water constantly at 195 degrees. Which option is more energy efficient?

Some pertinent information:
The temperature of the room where I keep the water heater is 65 degrees F. Unfortunately I don't have a measure of the insulation of the heater.

My own intuition from some barely recalled high school physics: energy input is the same in either case.
If the tank is well insulated, it does not matter. If it is not well insulated but you use a heat source with the same efficiency to heat your home, it does not matter either.

AM
 
Andrew Mason said:
If the tank is well insulated, it does not matter. If it is not well insulated but you use a heat source with the same efficiency to heat your home, it does not matter either.
Unless it's 80 degrees outside, and air conditioning is being used to cool down the room (to 65 degrees?).
 
If the tank is well insulated, it does not matter. If it is not well insulated but you use a heat source with the same efficiency to heat your home, it does not matter either.

Only if the central heating timer and the water heater timer are set the same, CH off Water on uses more energy.
 

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