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HW savings

Empire_2 Member Posts: 2,343
If you think about it,..If you were to set back the tank, say 20* during the night when it is not in use, you will need to raise the 40 gal of water back to its origional working temp which means the btu's used will be more than what it takes to maintain the dial setting out of the box. Usually for residential use the water is needed every day. 20 x 1.0(spacific weight of water) x 60 min= BTU/Hr


  • John Shea
    John Shea Member Posts: 247
    never really noticed what my hot water tank does...

    during the night. Does it run the burner? If so, how many times? Could anyone see a savings in fuel consumption (even slight) if one were to somehow throttle the tanks thermostat to 'vacation' during the night?

    I guess I'm asking if there's such a thing as a programable tstat for hot water tanks. If so, do you think any significant amount of fuel could be saved?
  • Constantin
    Constantin Member Posts: 3,796
    Well, here are some thoughts...

    ... the greater the temp inside the tank vs. the exterior, the greater the heat loss. Setbacks during the night are common, as it reduces nuisance cycling. How much energy it will save is open for debate. It's likely that insulating the tank will do more to prevent heat loss than allowing it to cycle down at night.

    A quality tank will lose about ½°F per hour, or about 1kBTU per 10 Gallons of capacity per day. That will add up...

    Anyway, depending on the manufacturer, the controls may be already built-in. I know the Viessmann Vitotronic 200 and up have night tank setback features and would be surprised if other brands like the Vision 1 controller, etc. didn't feature such control capabilities as well.
  • Dale
    Dale Member Posts: 1,317
    A little story

    Going on vac for a week and being lazy I didn't turn my water heater off just to Pilot, getting back from Vac a week later I turned it to on and didn't hear the burner come on. Saying @#$**%$ I went to light it and found the pilot on, testing at the sink the water was hot. So, just the pilot kept the heater at the 125 degrees I have it at. Heater is med. grade insul standing pilot, in an insulated basement, set to a lower temp. still the burner didn't run for a week in the summer. If you had electronic ignition maybe it worth it to do a reset but unless it's full computer control I doubt it.
  • Nick Dearing
    Nick Dearing Member Posts: 30
    Yes, but

    then you are saying if I set back my thermostat at night, and then raise it back up in the morning, it will take more BTU to raise it back up then it would have to keep it maintained. Right?
  • Ted_4
    Ted_4 Member Posts: 92
    Faulty Logic

    There's that old set-back myth again! The amount of btu's it takes to raise the water temp 20 degrees is the same as the heat given off while it is cooling 20 degrees. The savings comes while the water is being held at a lower temp. Standby loss is REDUCED during the setback period, saving BTU's.
  • Empire_2
    Empire_2 Member Posts: 2,343

    Correct me if I am wrong, but I agree that your statement is true, but you are going to be raising the temp of 40 gal of water, not air...also when it cools 20* no fuel is being used or wasted....bringing 40 gal back up 20*. BTU, the amount of heat required to raise 1 lb of water 1*f. 1 gal of water weighs 8.34lbs....Do you see where I am heading with this?
  • Ted_4
    Ted_4 Member Posts: 92

    Let's say we have a 40-gal water heater just sitting there. Due to standby losses, a certain amount of btu per hour is required just to keep the water at a constant temperature. If we lower the water temperature, fewer btu per hour are required to keep it at that temperature.

    When the temperature is set back for a period of time, no btu are added to the water until the new lower temperature is reached. Since we know the specific heat of water, we can calculate how many btu are given off by the water as it cools, and how many btu will be required to reheat the water to the original temp. These two amounts are the SAME.

    The savings from temp. setback comes from holding the water at a lower temp. for a period of time. The longer the setback period, the greater the savings.

  • Empire_2
    Empire_2 Member Posts: 2,343
    Ted, Got it/.

    I understand your explanation now. I should have seen this being that I could figure the amount of heat used to reheat the water back up to temp. SOmetimes I have a minor brain blockage or "Brain fart" and only see in 1 direction:) Thanks alot for the clairity..
    Mike T
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