Just heard the nightly news. They said to save on power [no shortage here] you should set your thermostat at 68 in the day and 60 at night. 55 when you are away.

Now, I use an air to air heat pump. The manufacturer says to keep the thermostat at one set temperature. If you lower the temperature and then raise it, it will kick in the resistance heater and use a lot more power.

My experience agrees with company. Why don't these people ever read the literature.

Cheers,,,,

Z

-- Anonymous, February 23, 2001

Answers

You're heat pump is an exception to the rule for heating systems. Yes, raising your temp 10 degrees will probably kick in the electric heat. But the question is: how long will it take to bring the temp back up to normal range where the extra heat is not needed and will the cost be less than the energy saved during your low temp cycle?

For "normal" gas-fired forced-air, gravity, hydronic heating systems, lowering the temp saves significant costs.

-- Anonymous, February 24, 2001

Z's 'experience' makes no sense because the room temperature is turning the system off and on via the thermostat. And often that can happen 10 times /hour. For longer periods (like when you be sleeping) a lower temperature will call for heat fewer times than a higher temperature.

MEASURE then speak.

Common sense tells you that if you are set to a lower temperature, the less energy will be required for heating and the cost will decline.

-- Anonymous, February 25, 2001

Ya'll leave Z alone on this one.

I saw a study (done by CPL or Duke Power, can't remember which) back when I was in NC. It showed that, when the temperatures outside are very cold and if you're only going to be gone from home for several hours (such as a normal workday), it *DOES* use more energy to constantly change the thermostat around. The exception is if you're going to be gone for several days (ie, a vacation). But for normal daily use, just set it to 68 and leave it.

The reason? The air in the house isn't the only thing that cools off (or heats up, in summertime). The walls, the furniture and the appliances all cool off, too. So ... you get home from work, the thermostat goes back up and the heat unit will cycle over and over again. It'll warm the air in the house enough to cycle off, but the cold fixtures will cool the air back down.

Cycle on, off, on, off. This continues until the fixtures in the house have warmed up enough to stop being a factor.

Not only does this use WAY more energy (startup is by far the most drain on the utility), it reduces the life of the heat unit.

(Imagine trying to heat a room after some big hairy guys have moved several blocks of ice onto the floor and you'll get the idea.)

Y' can't cheat the Laws of Thermodynamics. You're not just heating the _air_ in the house on a very cold day.

-- Anonymous, February 25, 2001

Everyone appears to be right about something here, especially Z. Basically, the problem is in the resistance heater(s) coming on when there is a large temperature differential (typically over 2deg. F) between the measured temperature and the temperature setpoint. When you yank the thermostat back up, you get the big differential and your dollars go out on the electric grid ;)

The heat pump is two or three times more efficient than the resistance heaters since the heat energy in the air itself is utilized, and this is the real cost difference, and why its best to set the thermo and leave it alone. But if I go away for more a day or more, its always cheaper to set it low, and 55 sounds pretty good. You will take a hit due to the resistance heaters for a very short while (it really doesn't take long at all) when you get back and crank the thermostat back up, but its still cheaper overall. And if you're really smart, you can try this trick (it works):

Slowly increasing the thermostat up a degree or so every 5 minutes or so - this way the heat pump is working without the resistance heaters - there's usually a light showing when resistance heaters are on. Eventually you will be back to your preferred temperature, without ever once "burning" the strips...

-- Anonymous, March 05, 2001