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wrote:
Craig wrote:
wrote...

I'm trying to save money on heating bills (i have a gas furnace), and
so i keep it pretty cold when i'm not home. I usually keep it around
60 degrees when i'm not there. But in the morning when i wake up, i
programmed the thermostat to 70 or so for a couple of hours.

Someone told me that that actually would cost more in the end, b/c the
furnace has to work harder to get the temp up from 60 to 70 everyday,
than it would to just keep it at a constant 65. But, like i said, its
a gas furnace and it heats up the house relatively quickly. Plus, my
home is older (built in 1940) and is not very efficient. So, I'm
afraid the heat would be running much more often to keep the house at
65-67 degrees throughout the day.

Any advice?

I think you're doing a good job now. Based on info from my gas company, if
true, a set-back of any amount will save money as long as the time at a
lower temp is a minimum of 8 hours. And the larger the set-back differential
and the longer the set-back period (above 8 hr.), the better for savings.
The gas company does suggest that cutting back temps for periods of under 8
hours may not result in a saving.

The folks that should worry about issues that you bring up are the heat
pump owners whose heat pump includes additional electrical resistance
heating for a quick early heat-up period.

Craig

The temp loss of a house is proportional to the temp difference. If
the inside temp is the same as the outside, there is no loss. Start
raising the differential and the bigger it gets, the more energy is
lost. So, setting back the temp for any period is going to save
money. As the house temp starts to drop, so does the heat loss.
When you restore the temp to a higher temp, sure the furnace is going
to run awhile, but this is just replenishing the heat in the house that
was lost as it cooled. If you do this overnight for example, had the
temp been left high, more heat would have been lost and the furnace
would have run longer during the night than it will now run in the
morning to restore the temp.

Bottom line, any setback period will help. The longer the setback and
the lower the temp, the more difference it will make.

One additional note. The above applies to oil, gas, pure electric
systems and similar. If you have a heat pump system which uses
electric as backup and you set the temp back far enough that the system
then uses the backup electric during recovery, that obviously changes
things. Also, with a heat pump system, you have the consideration of
what the outside temp is when it runs. If you set it back during the
day when it's warmer outside and then restore the temp when it much
colder, it will use more energy, so the setback may be a wash or even a
net loss.

For programable thermostats, I like the ones that have intelligent
adaptive recovery. On these instead of trying to guess when to have
it switch to the higher temp in the morning, for example, you just set
it to the time and temp you want. The system learns how long it takes
to make that happen and constantly adjusts it. Honeywell VisionPro are
super and you can get good deals on them on Ebay.