Originally Posted by racsan
but if its maintaing a constant 120-130 isnt that more effeicent than heating up a tankfull from complete cold? seems like if the a/c is set at a constant setting in the summer the power useage isnt bad, but if it keeps getting turned on the off based on when the house is occupied then more electricity is used. now if you were going to be away for a week or more, sure. but on a daily basis i think it would end up costing more to keep turning it down & back up.
This can be an easy problem to trip over if you're not careful in how you analyze it.
Basically, turning down a water heater's temperature during the day works to save money for exactly the same reason that timed thermostats save money by turning down your house's temperature at night.
The reason is that adding heat to your water or your house is an investment, no different than putting in new appliances or building a deck. So, if it weren't for heat loss through the insulation, you'd pay to heat your house once in October and then enjoy comfortable indoor temperatures for the rest of the winter, just as you enjoy new appliances or a deck to have bar-b-ques on for a long time after making the investment.
Unfortunately, that's not how it works. What you're actually paying for on your gas or electricity bill is not the heat you put in, but the heat you lose. You burn gas or use electricity to replace heat lost through the insulation.
And, it stands to reason that you simply lose LESS heat by having a lower temperature differential across the insulation.
In fact, even when you're water heater is heating the water back up in the late afternoon, or your house is warming back up in the morning, you're still saving money during this re-heating period because the rate of heat loss from the water heater or house is still lower during the reheating period than it would have been had you maintained a higher temperature differential throughout the day or night.
So, even though the gas or electric meter is running, the net effect is a savings in energy because you're replacing LESS heat than you otherwise would have if you'd maintained a constant temperature.
Certainly the potential savings would be lower by turning down a water heater during the day than it would for letting a house cool down at night, but that's because there is much greater heat loss through he exterior walls and roof of a house than there is from a water heater. Still, the savings would be proportionate to the amount of heat loss.
One way to REALLY save money is to turn the thermostat in your house down, and put on a sweater. Or, wear LONG underwear; both long sleeved undershirts and long johns. You do that, and you'll be surprised at how much you can save on your heating bills.
No lie. I've had tenants ask me to come to their suite in the winter to check the thermostat and zone valve because they're cold. They're in their suite wearing nothing but shorts. No shirt, no shoes, not even socks. They'd be butt naked except for the shorts. And it's 35 degrees below zero outside. It's no wonder they feel cold. Great grampa would hang his head in shame.