Assuming you have good windows, adequate insulation is there that much
advantage to setting back the thermostat( N/Gas heat), if it takes an hour
or better to stabilize the temp in the house.
If normal settings when at home are 72degs and setting it back to 66 at
Get a T'stat with a timer to come on about 15 to 30 minutes before you wake
up. Personally, I like sleeping in a cool room under a toasty electric
blanket. No reason to heat the rest of the house. I don't know what the
actual energy savings are, but the heater hardy runs at all during the
For seventeen years I owned a drafty fourteen room house dating from
the 1850s. At that time I was in the paid labor force with a school
age child, so we kept fairly regular wake up and bed time hours. I
installed a setback thermostat and reduced the oil bill by a
I now retired and live in a 1950s house which is much smaller and is
well insulated. I have not bothered to install a setback thermostat
because as we got older we were more likely to wake up in the middle
of the night. We prefer a warm house to a cold one when going to the
bathroom, having a snack or whatever.
I think one way to decide is to run a test to see how long it takes
to drop the temperature in your house from 72 to 66. If takes one
hour or less, then a setback thermostat would be a good idea. If it
takes five or six hours, then it probably would not make a
Good question. I would like to take itone step further. It's obvious you
will save energy if you lower the thermostat at night. But how much? If
you set it back 20 degrees and the boiler must fire a long time to get it
back to a normal temp are you really saving. Maybe it's better to only set
it back 5 degrees so the boiler doesn't fire as much but doesn't have to
over work itself to get the house back to a normal temp...
Someone must have this answer.
I recall seeing it. IIRC, the maximum setback should be 10 degrees or you
lose too much latent heat and yes, it is not as efficient. I'm sure there
are variation depending on what type of heater, home insulation, etc.
We keep ours at 70 for two hours in the morning, then it drops to 68 until
bed time, then it drops to 64. The reasoning behind the 70 is to warm you
up in the morning but then some activity keeps you warm for the rest of the
day. Heat comes on 15 minutes before my normal wake up time during the
week, about an hour later on weekends.
I'll try. Having the boiler fire for a long time during recovery doesn't
cost more than having it fire a little bit at a time all night.
The energy required to heat a house depends on the number of degree-days,
which is a measure of the difference between indoor and outdoor
temperature. If the setback lowers the temperature by 10 degrees for 8
hours, ignoring the time when it was cooling down 10 degrees, you have
reduced you degree-day total by 3 each day (10 degrees times 1/3 of a
day). Now in spring and fall it often won't drop the whole 10 degrees
because it's not that cold outside, and even on cold days it takes a
while to drop 10 degrees. So based on your weather you might try to
estimate a rough average number for the season; in Chicago, it might be a
reduction of 3 per day * 65 days = 200 degree-days. ballpark, and YMMV.
Next question: what is your energy consumption in therms per degree-day?
This can be calculated from data in your gas bill, and is remarkably
constant from year to year (whatever the weather, whatever the price of
In my case, the house needs about 0.3 therms per degree day. So 200
degree days reduction due to setback means I save about 60 therms, which
would currently have cost about $40. That's the saving for the whole
year. Not a whole lot.
I have not seen any postings with respect to the "overshoot" problem.
When a steam or hot water system is grinding away at full blast for
the time to raise the house temperature by ten degrees there is a
tendency for the radiators to stay hot after the thermostat has shut
off the furnace; this can cause a house temperature several degrees
higher than the thermostat shutoff point. This "overshoot" can be
uncomfortable and wastes some energy because the temperature
difference between inside and outside is greater.
Some thermostats have a "heat anticipator", a tiny heater that warms
the thermostat sensor so that it shuts off the furnace before the room
temperature reaches the setpoint. Tweaking the anticipator setting
can reduce overshoot, but not eliminate it.
A really good smart thermostat would include a computer (nowadays,
that's one cheap chip) running a model of your house, with inputs from
interior, exterior and wind-chill sensors. The hardware wouldn't cost
much, but getting the software (customized for your house) right would
be a bitch.
Nearly all older furnaces are more efficient if you run them
Therefore, if you let the house cool at night, then are "forced" to run the
continuously to warm it to a daytime target temperature:
a. You save money because the cool house loses less heat to the outside
b. You save more money because the continously operating furnace is
"Non-high efficiency" furnaces (I don't know what else to call them? They
used to be called "Standard" when I was in the business.) used to be
constructed to meet a code which calls for an efficiency which can be
Efficiency = 80% - a - b - c -d
where a, b, c, d are functions of the "off" time when the furnace cycles.
The longer it is "off", the higher a, b, c, and d are, and the less
efficient the operation.
The manufacturers deliberately limited the efficiency to meet the code
(ASHRAE?) which was intended to make certain enough waste heat went up the
chimmney to maintain a free-convection draft.
Many of the older furnaces barely make it to 50% efficiency on normal days
because the "off" time is so high. Half of the heat goes to the house,
half goes up the stack. When the furnace is operating continuously, a,
b, c, and d approach "zero" , and efficiency approaches 80%.
High Efficiency furnaces minimize/eliminate these losses by installing a fan
to force waste gasses up the chimney. That's why the newer High Efficiency
furnaces can do so much for your bill. You are substituting a 90%
efficient furnace for one with an 80% nameplate but which often performs at
Old Al (who hasn't fiddled with furnace calculations in 30 years)
I had a new variable speed furnace, and heat pump installed yesterday.
I asked the install technician, about setting back the stat at night and
during the day, he said he would not lower it anymore than 4-5 degs.
With my old heating set up ( nat gas ) I set the stat back to 66 at night,
it would turn on to 70 in the mornings, and run for 45 mins to achieve 70.
Then go back to 66 during the day till I got home from work, then up to 72,
till bed time.
With the new units,I leave the fan on 24-7 its running on low speed can
barely hear it, thermostat set at 71 degs. I will see how that goes for the
time being, maybe as the weather turns colder I will go the set back route.
HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.