I have heard that you should set your thermostat back at night no more than 8 degrees or so and that anything more than that requires the furnace has to work too hard each morning reducing your savings. But I am wondering about temperature settings for a home that is infrequently occupied.
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I have a weekend cabin in a very cold part of <!—-><!—-> <!—->Colorado<!—-><!—-> that I am able to visit only about two weekends a month during the winter. I have a propane, forced air furnace and I put the thermostat on hold at 45 degrees whenever I leave after the weekend.
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When I arrive, the furnace heats up the air in about two hours, however many of the surfaces stay cold for much longer. I was wondering if a higher hold temperature, perhaps 50, might actually result in less energy usage overall.
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How would you determine what hold temperature is warranted given the significant amount of time the house is not occupied? Any suggestions would be greatly appreciated.
Replies
If it runs two or three hours to get back to temp, how much run timewould Usave by lowering it the extra 5º? If you were not there for seeks at a time I would set it low enough so stuff would not freeze.
Below is a pdf from Canada on the subject
Bud
Thanks for responding, however I don't see the PDF attachment.
Well I tried three times, must be to big,,,
Its from this place The Canadian Centre for Housing Technology (CCHT)
Might be able to google it up..There is also a very large thread on the subject on this site , do a search...
Sorry
Bud
This has been done here before, so perhaps a search will turn something up. IMO the laws of thermodynamics would suggest that you would use less energy by turning the heat/air off when not in use (or just warm enough to keep pipes from freezing). I am not an expert on the subject however, so that's just my opinion, worth what you paid for it.
The heater/air does not really become less efficient during extended run times (in fact, I believe it's the opposite). I would set it as cold as you can stand, especially if you are not there very much. The 8 degree nightly setback seems to be BS as well. It is probably suggested because much colder than 8 degrees below typical room temperature and people start shivering!
more than that requires the furnace has to work too hard each morning reducing your savings
Well, that statement has a lot of unqualified qualifications--as does too much information on the topic, but that's been true since the 80s <sigh>.
If you have a single-speed furnace, it can only run one "strength," which is all the way on.
Now, from your description, your place is doing exactly what thermodynamics asks; seeking an equalibrium. So, the surfaces within are likely to remain cold after the air temperature "satisfies" the thermostat. Will setting the temp 5º higher affect that? Yes, enough to notice? I don't know.
Now, aiming for slightly higher equalibrium temperature, and it being "cheaper," oh my, that will drag out the "set back is rubbish" versus "set back is golden" arguments. There's no simple answer beyond, really, trying it, and seeing. The problem with that, of course, is that no one time period you self-test in will be the same. Might have been much cheaper last month; and awful last weekend.
All I could really do is speculate (which is generally better than pontificating, but much, much harder to not do <g>).
nightly setback is very different than extended setback.
Extended setbacks should be as low as you can do without risking freezing, condensation or damage to things in the house. If heat up time is a problem, get a phone switch installed so you can call the house the day before you go up and turn on the heat.
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I was always told that you shouldn't set it below 55 degrees or it will condensate in the heat exchanger and cause it to pre-maturely rust. is that correct?
I think 55 is the conventionally accepted low temperature for a house in general, but honestly I am not sure really. and I know even less about the mechanics of FHA systems, sorry.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
From all the good comments, it sounds like setting it at 45 is still the right way to go.<!----><!----><!---->
At that temperature (the lowest my thermostat goes to) the garage/furnace area gets to just above freezing, so lower would not be a good idea. I also turn of the well pump when I leave just in case the power gores off and something does freeze. <!----><!---->
I have considered the telephone call-in feature to the thermostat, so perhaps I will do that and just make the call when I leave home (two hours away). I had not heard about the 55 degree lower limit, however nothing ever seems to rust in <!----><!----><!---->Colorado<!----><!---->, so perhaps that is not a problem here. And even when it is set to 45, the furnace still runs fairly often.<!----><!---->
I guess the only way to test the theory is to use a setting of 50 next winter ands see what it does to my propane bills!
Ok I googled it and found the link for the pdf/
https://www03.cmhc-schl.gc.ca/b2c/b2c/mimes/pdf/63816.pdf
But this is a nightly set back scenario.. What you are looking for is a long term one...I had a house in N Denver that was vacant for several years and would set it to 40º in winter and it would keep the pipes from freezing. Short of draining the pipes, (not uncommon in Mtn cabins).If you can keep pipes unfrozen all is well..
Bud
We've been over this repeatedly. Except for heat pump systems (and maybe a few exotic systems of some other sort), you never lose by "setting back" a thermostat, and the more you "set back" the better. A furnace (save for the afore-mentioned heat pump) does not have to "work harder" but simply runs longer when recovering from a setback. And furnaces are MORE efficient when they run longer than they are on short runs.
However, beyond a certain point (mainly dependent on outdoor temp) the advantage of further setting back diminishes significantly. Also, as you may have noticed, when you bring the temp up after having it quite cold, you may in fact have to elevate the temp above "normal" in order to make it comfortable, due to cold surfaces.
But if you're simply bringing the temp up to "normal" then the greatest possible setback is the most efficient choice. Your real tradeoff is relative to comfort/convenience.
Thanks for all your help, guys. I'll stick with the 45 degree setting and maybe buy a couple of electric blankets, since getting into bed on Friday nights is always a bit chilly!
...since getting into bed on Friday nights is always a bit chilly!
Ahh.....why didn't you say that to begin with?
You just need a dog.
Democrats.The other white meat.
Yeah, the real lower limits are these:-- Some plumbing areas may drop 5, 10, even 15 degrees lower than the thermostat setting. Thermostat needs to be set to assure that the coldest area containing plumbing remains above 32 degrees. (Sometimes it's wise to add a little insulation to these areas, or install heat tapes or some such.)-- As temperature drops, relative humidity increases. You generally don't want to cause temperature to drop so much that significant amounts of condensation occur in areas such as the drywall behind a dresser, resulting in mildew or other forms of moisture damage. How much of a drop you can tolerate depends on the RH that you start with and the degree to which there are colder, moisture sensitive areas in the house. Keeping the circulating fan running (or putting it on a timer) can help in this regard, and also help with regard to the plumbing issue.-- Wood furniture, pianos, and similar items don't "appreciate" frequent wide temperature swings. If your decorating taste runs towards WalMart or IKEA this probably isn't a concern, but if you have a number of antique wood items (or a grand piano) then it's worth thinking about.
So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
Be very aware that whatever you set your T stat at it is only that temp at THAT spot. Think about it. Your house has different temps warmer and cooler and none of us know the temp around the water pipes at any given location. It only takes one spot to freeze and burst a pipe. I've lived up in cottage country in Canada where we constantly went into houses/cottages with burst pipes. Even places that had alarm systems that notified agencies of a failed furnace. In these cases the sensors were in the wrong place and by the time the temp dropped to activate the alarm, pipes in certain places had already burst. One of the things that cottage owners always did was to open the cupboard doors underneath each sink (on outside walls) when they left for extended time because the temp inside the cupboard (where the pipes were) were always colder than the house.
roger
I think that is good advice, although my cabin has SIP walls so that shouldn't be a problem in most of the house. The garage where the furnace and water heater sit does get colder, so perhaps a few heat tapes in that area might be a good idea.
danh, you can't separate comfort from the equation.First, setting your thermostat above normal after coming out of the setback is kind of offsetting the benefit, isn't it?Never mind the fact that with FHA you *won't get comfortable*, no matter what you set the thermostat to, for awhile. Air simply doesn't transfer heat to those cold objects very quickly at any temperature you can stand for an air temperature.So yeah, you can save money if you turn back your thermostats. you can save a lot of money if you turn off the heating system entirely, or run it at 40 degrees and wear a parka, but we don't do that because it's uncomfortable.So if you do your setback and the price you pay is that it feels chilly every morning when you get up, then aren't you kind of defeating the purpose of having a heating system, and furthermore IF YOU AREN'T GETTING MUCH BENEFIT, aren't you wasting your time???In the standard leaky oversized FHA system home in our country your setback makes sense, to a point, though it does come with a comfort tradeoff in the morning. I don't want to overshadow that or minimize it; most people reading this will find your statements completely accurate.But your blanket statements do NOT apply to a large number of more efficient modern homes out there today, and so while you may be exasperated that people bring this up, you need to temper your broad stroke response a little bit. Radiant systems, for example, are not "exotic" anymore. Systems with outdoor reset temperatures are not "exotic" any more and you cripple their heating curves if you set them up to handle heavy setbacks. Modulating air furnaces and boilers are not "exotic" anymore and do not benefit from having to actually work harder, which they do, coming out of setback.So please, keep the parameters of mass, tightness, and heating system type in mind. They matter.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
> First, setting your thermostat above normal after coming out of the setback is kind of offsetting the benefit, isn't it?Yes, that was my point. If you simply do the numbers you always save money with a setback. But factor human nature into the equation and it may be different. And every human is different. So the best approach is to help the consumer make an informed choice.As to my "blanket statements", they DO apply to essentially all single-source/single-price heating systems, regardless of how energy efficient the are. The thermodynamic principles don't change.(I don't know about modulating boilers, but modulating GFA furnaces are definitely more efficient in "high".)
So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
Generally, modulating appliances run best at low continuous fire, though I am not an air system expert for sure. In hydronics land (also not exotic, these days) they are generally condensing appliances that run much better, cooler. if they are set high enough temp to make setback recovery an option, you sacrifice efficiency every second it fires for the life of the boiler.All I'm saying is statements that do not call out the affecting parameters don't help the discussion.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
Certainly condensing units are subject to a lot of variables, and I'm not familiar with hydronic systems. But residential GFA units are "tuned" for max efficiency on full speed -- the modulated rates are intended to permit lower fan speed (less noise) and tighter temperature control. (Plus many GFA units benefit from "warming up" on low speed for a minute or two anyway, so it's taking a necessity and making it a "feechur".)But you do have a point, which I tried to make indirectly. With heat pump systems, eg, you have two "sources" -- resistance and heat pump -- and with pure electric you may have time-depenendent (or, in other countries, load-dependent) rates. Any factor that causes the $$/btu to vary with load or time of day needs to be taken into account.
So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin