I have a question regarding programable thermostats. We have a 1960’s rambler, insulated pretty well, but windows are old. Will probably replace them in the near future. We heat with natural gas. Both of us are gone for about 10-12 hours Monday through Friday, so I’m considering a programable thermostat. Is it better to leave the house at a consistent temperature all day, or is better to have it drop the temperature while we are gone during the day. Do you use more energy and heat maintaining a temperature, or use more getting it back to temperature if you’ve had the thermostat drop the temperature the hours you’re out of the house. And if dropping the temperature is the way to go, how many degrees can you drop it during daytime hours before it’s no longer cost effective. As always, thanks in advance.
Discussion Forum
Discussion Forum
Up Next
Video Shorts
Featured Story
Listeners write in about a fondness for palm nailers, German translations, and insulating behind masonry.
Highlights
"I have learned so much thanks to the searchable articles on the FHB website. I can confidently say that I expect to be a life-long subscriber." - M.K.
Fine Homebuilding Magazine
Fine Home Building
Follow
-
Fine Homebuilding
Dig into cutting-edge approaches and decades of proven solutions with total access to our experts and tradespeople.
Start Free Trial Now -
GBA Prime
Get instant access to the latest developments in green building, research, and reports from the field.
Start Free Trial Now
Replies
Perhaps someone else will chime in here soon, to ask you all of the right questions, so that they can get to theright answers.
Your question depends on too many variables. Like: what type of heating system do you have, and how long does it take that system to raise the temperature by a few degrees? How good is the insulation, and how bad are the windows? What is the cost of natrual gas in your area? What is the average winter temperature outside?
Unless you're the lead dog, the view just never changes.
The rate of heat loss is proportional to the gradient, or difference, in temperature between inside and outside. There's no question that maintaining a comfortably warm home for many hours while the home is empty is a waste of energy. Utility companies always advise to turn down the thermostat during the day (if no one is home) and at night while sleeping.
I installed a programmable therostat last fall and set it to drop the house temperature to about 50F during the day; I also set the temp back at night. I had to experiment with the time settings such that the house was warm upon my returning home or when getting up in the morning. The only downside is that if I returned earlier than expected in the evening, I had to wait for the house to heat up. As I have steam heat, this is longer than for forced air.
I sure wish someone would study this issue extensively and provide some graphs showing the answers. YOu would need heat loss of building, temperature differential, price of fuel (I think) maybe something else.
This discussion comes up a lot among old house people. There are some that say a constant temperature is more efficient. Personally, I THINK it is advantages to have set backs.
More to the point, the Honeywell thermostats are good but pricey. I had problems with Hunter ones maintaining their accuracy. Currently, I have White and they seem ok. But be sure to think about your schedule and how many program changes per day and which days matter to you. Many have a weekday and a weekend program, so that if you work at home every Wednesday, you have to change it manually. Others have a seven day programmability, which if you have fixed schedule that varies on certain days will be better.
would study this issue extensively and provide some graphs showing the answers.
Well, you give most of the "why not" answers. The calcs tend to be closely realted to the building and it's occupants. The economy is definitely linked to the cost of fuel, age & efficiency of the mechanicals, and, biggest of all, occupant tollerance.
Now, if you are someone selling programmable stats, you can make claims rather readily, as the round stats don't have a nice digital readout for either the "read" or the "set" temps. Otherwise, you could just measure how much less the mechanical system runs for, say, every degree change in the set temp. You'd need to know that versus some known time.
But, if somebody changes the set temp, it blows the whole curve. It makes for frustrating research, I can tell you. It will send you off to just go use computer models, even those in Fortran and designed for punchcards . . . <weary sigh> (didn't even get a t-shirt).Occupational hazard of my occupation not being around (sorry Bubba)
Good morning.
Yes, the programable thermostat will save you money regardless of the conditions it is operating under. I installed one about three years ago and have not regretted it.
If I recall correctly, the installation instructions said not to have more than 10 degrees differential between the highest and lowest settings. Mine has a seven day program. Overiding the preset temperatures is done by pushing a button (manual setting) and then bumping up the temperature setting to where I want it. At the end of the programed time, it goes back to the automatic settings.
The one I bought is used for heat in the winter and central air in the summer. It works great and I wouldn't be without it. Bought it at Home Depot for about 40 bucks.
check with your gas company, they may have a rebate program, got $25 from them to change my thermostat.
and, is this really your first post?
bobl Volo, non valeo
Baloney detecter
No, this isn't my first post. I've been posting here and on Knots for probably 5 years. I'm not sure why my info said first post. I need to take a minute soon and update my profile with some information.
I know that there are many variables that factor into my question. I knew asking it that there are many things that contribute to calculating heat loss. I was just looking for an "on average, do programable thermostats help." I appologize for being vague on details.
Our house is a 60's rambler, walls are insulated well, although only 4 inch walls. Exterior is redwood siding, interior is sheetrock with plaster over the top. Ceiling has an abundance of blown-in insulation. Poured foundation, unfinished basement. Windows are original, single pane Anderson sliders with single pane sliders with metal single pane storm windows made from a local company. Furnace is a couple years old, natural gas, forced air. Doors are newer exterior doors that seal well. Attached, unheated garage on north side of house. The house is 1000 sq.ft on the main level, same in basement. Climate is north-western Minnesota. Very cold. Not sure of the average temperature, but lots below zero. It's very windy all year long, so wind chill is often at horrific levels in January and February.
I know that our major weakness, besides being an older house with 4 inch walls, is the windows. I'm working towards getting them replaced, just can't quite afford it. Still researching my best options for window replacement. Hope some of this info helps. As always, thanks in advance.
Setting back the temps WILL save money. How much? Depends.
Changing the windows won't save a lot of money. Sealing around the windows, weatherstriping will save. If you make the house to tight, you will need to add combustion air and make up air.
Hope that is general enough. lol.
"Do you use more energy and heat maintaining a temperature, or use more getting it back to temperature if you've had the thermostat drop the temperature the hours you're out of the house?"
The simple answer is that your house will loose more heat at a higher inside temperature than at a lower temperature.
The other issues are the ability of the furnace (when you said that you heat with NG, I am taking that to mean forced air) meet the load, the thermal characteristic of your house and the consistency of your schedule.
"And if dropping the temperature is the way to go, how many degrees can you drop it during daytime hours before it's no longer cost effective."
This will require some experimentaion on your part, but based on my personal experiments/experience, however much of a temperature drop that your system can recover in one hour. For a mojority of situations, this tends to be about 10 degrees. This, however, will depend on many factors; wall construction, outside air temps, prefered inside temps, and excess capacity of the heating system.
IF, your system is way oversized, any setback will work fine. IF the system is "right sized" i.e. just big enough to meet the steady state load on a "design day", then no set back is recommended, at those conditions. For instance, my system is sized for -10 degrees OAT and 65 deg IAT. When its 10 degrees outside or less, there is not enough excess capacity in my system to recover from a set back, so I leave the thermostat set at a constant temperature. With the exception of those very cold (for my location) days/weeks, I use the setback constantly. You will save energy and in the summer (if you have an AC system) you will be more comfortable. This is because if the load in the house is allowed to buildup, when the system is run to catchup, there will be a greater run time and more effective dehumidification.
(when you said that you heat with NG, I am taking that to mean forced air) FYI ther are a lot of NG forced hot water systems
bobl Volo, non valeo
Baloney detecter
Up here in Ottawa, Canada, the rule of thumb is don't set back more than 4 deg. Celsius (which is about 8 deg. F). We probably have similar winters and my house is 125 years old. I noticed an improved with the programmable thermostat and it also makes for more comfortable sleeping at night when the temperature sets back. Get the programmable thermostat that has the schedule flexibility you need and seal the windows as best as possible. Might even try using a temporary/seasonal caulking called 'draft stop' until the new windows are acquired. You'll notice a big difference.
Snipes
There is only one caveat to lower setting is always better, but it does not apply to nat gas.
The caveat is for heat with a heat pump and high thermal mass house that has time of day differential electric rates, plus the basic fact that Heat pump (air-air) COP ( or HSFP) is dependent on the outdoor temp. We actually let the HP run in the early evening (8-10PM) when the outdoor temp is still warmer (so HP COP is higher), and let that heat store in the mass for the night and early morning. Totally off till about 9AM. Leave air-air HP on during the day when outdoor temp is higher.
Oh, BTW, Henry Hub nat gas prices (wholesale) have gone past $14 MBTUs (about $1.45 per therm, add on 50 cents for delivery and nat gas soon is over $2) which equates to 6.8 cents kW-hr for resistance heat. With a HP at 25 deg F, you get that same $2 therm worht of heating for $1.14 with elec. at 10 cents/kW-hr.
Looking into buying some stock in single players in the heat pump business, looks like the market will be set to take off in coal fired generating plant areas, those in nat gas fired plant areas may be SOL.
And if dropping the temperature is the way to go, how many degrees can you drop it during daytime hours before it's no longer cost effective. As always, thanks in advance
You've asked some critical questions. There was a quoted amount of savings per half-degree change in stat setting in the article a couple-three issues ago.
You have neatly defined your home situation, too (thanks muchly). That helps define things.
I have a similar situation in that my house is typically vacant for a definable time. I use a 5+2 stat.
In a/c season, the a/c kicks on for an hour about the same time as I get up. Then the setting changes to about 4º higher (about 1-2º above 'comfortable') and stays that way until 1700. Then it's down again, and runs that way until I get home or get comfortable. That setting holds until about 2300, when the temp is allowed to creep up to about 1º over comfortable (with a fan running, and factoring, a little for cooler night time temps).
In heating season, it's similar, a "bump" of warmth with the alarm clock, and then down again. Another bump about end-of-day, and then right down chilly (65º indicated--about 65.5-66.5º actual) overnight (blankets on the bed).
Versus a "single" setting stat, I'm saving about 30-40% in overall costs. Versus the previous owners, I'm saving closer to 60-70%, but they had dogs & kids in the house (and a plain round stat on 20 y/o mechanical equipment).
If I would get a bit more aggressive in coping with infiltration, I could probably get another savings in both energy bills.
You will always save money dropping the temperature of the house for hours at a time. Since your insulation is poor you will save more than average. You will certainly save more than the cost of the thermostat.
You'll save at night too.
I like the 7 day thermostats. They are no harder to program than the 5 day/2 day models.
It isn't practical to drop the house too much. High efficiency natural gas furnaces have a minimum ambient temperature at which they are rated to run. Mine is 55°F. If it runs when the air is colder than that there is excessive condensation in the burner and it may not operate. I set my daytime temperature to 60°, beginning about ½ hour before I leave for work. And I set the night time temperature to 65°, but with some more blankets it could be set colder.
Be very careful about which thermostat you choose. Many manufacturers models require batteries to operate. If the batteries die, you don't get heat. That's an inane design to have your pipes freeze just because the battery in the thermostat failed. Many thermostats loose their program when you change the batteries, so you have to reprogram them over and over. Some, but not all, battery powered thermostats have a back up mechanical thermostat preset to something like 40° so you should not freeze your pipes (assuming the pipes are not in an area more than 8° colder than where your thermostat is).
I like the Carrier thermostats. They don't need a battery, they don't loose their program even if utility power fails for a week, and if the program is lost the default heating temperature is 70°F. They do require one additional conductor in the wiring from the furnace, so you'd probably have to run new wire, which might be really easy to do depending on the route.
Thank you to everyone for your advice. All of your input on this topic is greatly appreciated. Because I'm gone for atleast 12 hours a day, I think the programable thermostat is the way to go. I think I'll go shopping for one this weekend. I think my next post will be in regards to window replacement. Thanks again.
You may not save a darn cent!
If your wife comes home and raises the temp on the thermostat beacuse "it feels chilly in here", no matter how carefully you have programed the thing, and how advanced it is, up goes the heat until she feels toasty.
Daughters are worse.
Want to get into REAL trouble? Tell them to wear a sweater.
Been there. Done that. Got the T-shirt.Quality repairs for your home.
AaronR ConstructionVancouver, Canada
Others have covered the setback issue, and I agree. The laws of thermodynamics are clear. Set it back as far as practical, given considerations of pipes freezing, plants dying, ability to recover the temperature, and whatever else occurs to you.
FWIW, I just put in a Honeywell Visionpro model. It has an adaptive control that learns what run time is required to reach the target temperature at the target time. For instance, if you get home at 530p, you set the thermostat to the target temperature at 530p. Apparently, after about 5 days it figures out when it has to turn on the heat (or AC) to be at the set point at 530p. Might save you from some guesswork. It has lots of other cool features too. One that we've discovered is quite effective is a circulation mode for the fan that guarantees that the fan runs at least 35% of the time, even if the heat or AC aren't running. The good thing about this is that it keeps the temperature throughout the house a bit more even, reducing monkeying with the thermostat because of warm/cold spots.