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We have a radiant heat hot water system in our house. It is heated with a natural gas Weil McLain high efficiency boiler (2008). We are going away for 2 weeks and have traditionally lowered the temperature in the house to +13C while we are away.

Some people have suggested that there is no energy savings with turning the heat that low and I should only turn the heat down a few degrees. I can see teh argument if I let the heat drop that low overnight, but if we are away for two weeks, it seems that the lower the heat the better.

Has someone does a study of this or have a link to a resource that has studied the issue? We are leaving tomorrow and I neglected to call our utility provider (they are closed for the weekend now).

We live on the prairies with overnight lows expected to be -20C and daytime highs -15C.

Thanks
 

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The lower the better, but not to freezing (for energy conservation). Most thermostats have a setting that they can't go below. If you have house plants though, you may wish to stay at say 10C or above...
 

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No house plants and we have a low temp sensor in our centrally monitored alarm system so if there is a low temp warning we'll get notice and have a local person let the heating company in the house.

Do you know of any resources that discuss the issue. My sister in law (the expert - self proclaimed) says that the energy used to raise the house back up from 13C to 22C outweighs just lowering the temp from 22C to 18C and then turning it back up when we get home.
 

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Your sister-in-law is incorrect. She doesn't understand the science involved in programmable thermostats at all, which is proven. The longer/lower you are from the "at home" setpoint, the more energy is saved. You can tell by how long the furnace is on to bring the heat back (say an hour or two), relative to how long the furnace would have been on had you not set the temperature back (much more time).

It is true that the major portion of the saving is the first few degrees, but there are further savings for the next few degrees too, down to the point where you meet the outside temperature and no heat is required at all. The lower you can set the temperature, the more savings there are, especially if you're away for a couple of weeks.

This discussion is strictly from an energy standpoint and has nothing at all to do with comfort - which is why people purchase programmable thermostats - so that the furnace can come on before you need the heat in the home, so that it's comfortable when you get up, or when you get home from work. This doesn't (usually) work for 2 week vacations, however, some thermostats can be remote controlled via the web and heat the home in time for your return from vacation, or you can simply turn up the thermostat when you get home from vacation and the home is usually warm again in an hour or two.

Programmable thermostat link:

http://en.wikipedia.org/wiki/Programmable_thermostat
 

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57, I see your point. I just got off the phone with a friend of mine who is an electrical engineer. He said it is a very good question for the mechanical engineering department at his firm (no real help today). He says they wrestle with this on commercial buildings all of the time.

Part of the issue is how much energy it will take to reheat the air, but the bigger question is how much energy will it take to reheat the structural materials that have dropped to 13C. The plaster, drywall, wood flooring, carpet, etc. All of this material absorbs heat during the heating season and will lose heat when you cool the house down.

If the house never needed to be warmed up again (i.e. if you left it a 13C until spring), then I agree that the lower the better, because you wouldn't have to heat the structure up to 22C. But we will when we return in 2 weeks, so that is the reason for the question ... :)
 

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Keeping the structure at temperature takes more energy than reheating the structure to temperature. (assuming similar outside temperatures at both ends of the journey) Yes it does take more time to reheat the structure than the air, but that again is a matter of comfort and not of energy consumption.

The energy utilized to raise the item (structure) to the original temperature was the same in both scenarios and is often forgotten by the individual who suggests not lowering the temperature. The energy required to keep anything at an elevated temperature is higher than if you allow the temperature of that item to drop for a period of time and then reheat it. If that were not the case, we would have a brand new source of energy on this planet by tapping into this "magic energy" that people believe exists in structures. ;)

Please, do not confuse energy consumption with comfort - they are often inversely proportional - one sacrifices (what most people call) comfort for the sake of energy savings. Although large temperature setbacks on a daily basis do not save much additional energy, they do save some additional energy and when extended for longer periods of time - a 2 week vacation - a lot of energy is saved.

You simply need to look at your heating bill in the winter if you go away for an extended period and lower the thermostat, or your cooling bill (that portion for A/C) in the summer if you have A/C and raise the thermostat. The bill would include the reheating or recooling of the structure. Of course, these bills would need to be adjusted for heating/cooling degree days. If you had a really mild winter or a cool summer, the savings would not be immediately visible if you didn't account for heating/cooling degree days.
 

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Grover you are asking about cost right? In that case turn it down. Read this.

http://www.ag.ndsu.edu/news/newsreleases/2008/feb-28-2008/thermostat-setbacks-do-pay-off/

According to the U.S. Department of Energy Web site http://www.eere.energy.gov, you can save about 5 percent to 15 percent per year on your heating bill by turning your thermostat back 10 to15 degrees for eight hours. That’s a savings of as much as 1 percent for each degree if the setback period is eight hours long
Being the US temps are degrees F.
 

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The longer you are away, the more you stand to save for each degree of set back. The rule of thumb I use is to adjust the temperature no more than one degree for each hour it is set back. (I have no proof for that, it just sounds reasonable from the evidence I have read.) For extended periods, like a vacation, the more it is set back the more will be saved. That must be balanced with the likelihood of damage due to cold temperatures (such as condensation, water pipes freezing or pets/plants dieing.) Keep in mind that extreme regions of the house could get colder than where the main thermostat is located. That is especially true of older houses. Some plants benefit from cooler temperatures in Winter so it could actually do them some good. All but the most sensitive plants can withstand temperatures down to about 5c. 10c-15c is not unreasonable for a vacation set back. It will save a significant amount of money for an extended absence.
 

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I would like to add, if you have any cupboards with water pipes running through them, (under kitchen sink) leave the doors open so the heat can get to the pipes and tell who ever is looking after your home about that, so they don't close them. With the lower temperatures in the home, and the -30 -40C that the prairies can get, frozen pipes could be a problem unless you intend on shutting your water off, and draining the pipes. Insurance companies recommend shutting off the water when leaving for extended periods.
 

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Turning off the main water supply is a good idea. Setting the water heater back or to off/pilot will save even more energy and help prevent damage if the tank accidentally drains. Just don't expect hot water for a few hours after you get home.
 

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I usually open the blinds on south facing windows to get some solar gain and open all bedroom doors to even out temp throughout.

I used to set temp to 15C when on longer holidays in winter. Some of my plants wilted but didn't die at 15C, so yes consider the plants. However, I think OP said no plants in his house.

Turn water heater to "holiday" setting if there's one, otherwise, about 1/4 from zero would be a good setting.

Depending on where you are and the forecast lows, you may want to shut off water main, add plumbing anti-freeze on all water fixtures - toilets, sinks, tubs, shower, laundry, etc. Think storms and power failures.

Finally, check with your insurance policy. I think mine says that if house is vacant for more than four days, it should be winterized (e.g. anti-freeze) or house is visited once every four days (or some wording like that). Otherwise, if pipes freeze and burst, insurance co. may not cover you.

P.S. Enjoy your holidays!
 

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When I'm away more than a couple of days, I always turn off the main water shutoff valve. This would prevent a possible horrible flood if something burst (not due to freezing necessarily) - Flexible water lines to dishwasher and washing machine for example... Also if some mischievous children were to turn on the water outside (in the summer).

Earlier we discussed energy consumption. We did not address Time-of-use power, which can play into when you would turn on say the A/C (or electrical heat), but that's more for daytime concerns and not a vacation... you would try to avoid running these major power draws during peak times as much as practical if you're on TOU.
 
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