Save by turning down the thermostat....

It's been said time and time again that turning down the thermostat saves money. At what point might this not hold true anymore?

I have a 1300 sq foot ranch with decent insulation. I have a lot of big windows which are my biggest heat loss. The forced-air natural gas furnace is a 90% efficiency unit, 80K BTU. If I allow the temperature in the house to drop to 58F while I am at work, the furnace has to run about 2 hours before the house is 68F and holding. If I had not turned it down, i'm not sure that it would have run 2 hours cumulatively over the course of the day.

Obviously there are a lot of things to consider, but I'm wondering what might be the simplest way to determine a what point it no longer becomes worthwhile. If I'm only saving $.30 a day for instance, it might be better for the house to just to maintain the temperature?

There are obviously some knowledgeable people here, thus I'm interested in hearing other's ideas on how this works.

I have all new windows, most walls are still R-7. I do have some R13 in some walls, a 3 season porch on the front corner, a sunroom off the back that is R19 in the walls, 1st floor is about 1500 sq ft now.
Our Temp falls about 4-8 degrees in 8 hours depending upon outside temps
I actually turn the heat down to 60 when I am the only one home
It was 69 degrees when my wife went out about 9am, its still 66 in here - sunny day but its only 25 outside. At times I will even shut the boiler off for the day, other wise it comes on 2-3 times. Probably not a good idea in the winter - since if I forget to turn it back on there could be a problem

At some point the house will lose heat at a much slower rate.
You would need an accurate heat loss calc & need to know how much it lost at different temp to figure this out. I just know having a programmable thermostat has saved us a lot on heating

The bigger the difference in temperature between the inside of the house and the outside, the faster you will lose heat. The better the insulation you have, the the slower the heat transfer, but it still depends on the differential.

One thing I don't like is if you have the heat turned down longer than you have it at "normal" levels is that the mass of the house can cool off to the average temp. This means the air may get up to temp, but the walls and furniture are that much colder and seem to pull the heat away from you.

So, yes, lowering the temp when you are not there does save energy, but you have have some comfort issues that could range from minor ot annoying...it depends on the furniture you have, where you like to sit, how cold it is outside, and how long your drop-down period is. I'd have to double-check...it's been awhile since I researched this, but I think it was about 1%/degree/8-hour period savings on average.

One way to handle this is with a "smart" programmable thermostat, like the Honewell FocusPro 5000 series. They monitor temps, and if you program it to be 70º at 6:00 PM, it figures out what time it has to turn on to be at that temp at the specified time.

jimbo said:

One way to handle this is with a "smart" programmable thermostat, like the Honewell FocusPro 5000 series. They monitor temps, and if you program it to be 70º at 6:00 PM, it figures out what time it has to turn on to be at that temp at the specified time.

Click to expand...

I have two Honeywell RTH7000 programmable thermostats that I bought at Depot or Lowe's about two years ago that do just what Jimbo described. They work especially well with heat pumps because (in the morning for instance) it starts warming the house early enough that the aux heat never comes on. They cost around $100 each, but I feel they're well worth it especially if the auxiliary heating element never comes on. Hope that helps.

That's a nice feature
If my thermostat ever goes I may buy one
Actually I'll need a 2nd thermostat for another zone soon

You can't tell that to old people!


They've got the heat up to 80 because their skin is like paper. Then they wonder why you're sweating just talking to them.

http://www.homeenergy.org/article_f...le=Thermostat_Setbacks—Do_They_Really_Work?

http://irc.nrc-cnrc.gc.ca/pubs/fulltext/nrcc50859/nrcc50859.pdf