I keep mine at a constant 68 or 69 because I don’t have any kind of consistent schedule - as my posting at 3:25am might indicate. But even that is too cold for me since I like run around in shorts and a t-shirt. Fortunately, there are some idiosyncrasies in the construction of the house that let me get by. The room with the tv is elevated by a couple of feet so the warm air tends to migrate there resulting in a reading that is at least 6-8 degrees warmer. The only other room I spend a lot of time in is my “office”. That has a couple of computers running 24/7 and they are like little space heaters, so that room is at least 8 degrees warmer than the hallway just outside the door where the thermostat is.
True, I forgot about Cold Ethyl!
Regarding the thermostat:
Cecil taught us that turning down the thermostat, then turning it up is good vs. leaving it at one setting.
However- in the case of my air conditioning unit, if I set the thermostat up high during the day, then come home and turn it down so that it runs for a long time to cool the house down, the extended run time can freeze my AC unit to the point of breaking down! I learned that 80 degrees during the day, then coming home and turning it to 78 saves my unit. Leaving it at 78 wastes my money (big difference in electric bills, believe me), and trying to lower the temp to 77 or 76 is asking for a broken AC unit.
You had a broken AC unit to begin with. No properly working unit would do this.
That article stunned me. I seem to be perpetually amazed at people’s foolishness. I never dreamed that some people just leave the heat on at max all the time - these are probably the same people who complain about their heating bill, too.
You can pry my programmable thermostat from my cold, dead hands. Or rather, my nice and warm hands because it’s set to turn on 15 minutes before we go home, and, having a small house, it’s already pretty warm by then.
Moderator note: There were three different threads on the thermostat being turned down column; I have merged 'em all into one.
I’m willing to bet you either have a refrigerant leak or it wasn’t charged properly to begin with. Low freon will cause the evap coil to ice up. Other possibilities could include dirty evap coils or a fan that isn’t blowing hard enough. You should probably have someone out to check on that, but in the mean time make sure the coils are nice and clean. A temporary fix is to figure out how long it takes to ‘break down’ and before that happens turn the AC off but leave the fan running (change the setting from Auto to On on your T-stat and move the Cool-Off-Heat slider to Off) this will de-ice the coils fairly quickly.
This thread has been active for five days, but no one has mentioned the biggest problem with setback.
To permit setback, the furnace must not only be powerful enough to keep the house warm, but powerful enough to warm a cool house rapidly in the morning even on very cold days. The latter requires roughly twice the heating rate of the former, and such furnace oversizing leads to reduced energy efficiency. It’s the same reason a Ferrari’s engine is less fuel-efficient than a Toyota’s at 65mph.
Most furnaces are 2-3 times the size the homes actually need for steady heat, and this results in more profit for manufacturers and installers. Installers also do it to cover their asses—after all, owners will complain much more vigorously if they are cold than if they are losing money. The better installers will do something called a heat load calculation, but that calculation method is very conservative and still prescribes at least 50% more capacity than you actually need.
If you can set the temperature back 5-15F and still have the house be warm in the morning, you have a humongous furnace and are just pouring money down the drain. A little savings from setback won’t make up for that.
The most efficient setup is a furnace that has to run flat out just to keep the house warm when it is -15F or -20F in Chicago. (The customary “design temperature” for Chicago is -15F.) If you have any setback at all, the furnace won’t be able to handle recovery (warm the house back up) on a cold day, so don’t do it. If it ever gets to be -26F again, the house will cool off a bit, but such temperatures never last very long so it’s not a big deal. And your home will be much greener than it probably is now.
[But yes, if you’re stuck with the monstrosity you now have, setback works.]
Thanks; I was seriously confused. I didn’t remember all of that discussion in the one I posted to!
If you’re comparing equal year of manufacture, fuel, and quality furnaces, do you have a citation that says the larger furnace will be less efficient?
I’ve been under the impression that for most new homes built since the 1980’s, only the cheapest, smallest size which will heat the house furnaces have been installed as “builder grade” products. Do you believe that’s incorrect? It certainly has not been the experience of any of my co-workers, who often have to perform major furnace/heat pump repairs within the first 2-5 years of operation.
I think the latter case is the more common. Most homeowners don’t have the option of getting a new $3,000-$7,000 furnace, as opposed to a $0 to $150 programmable thermostat.
Following up on my post above, it is not that difficult to estimate how oversized your furnace is, if it is a one-stage furnace. It helps a lot if you have a slightly fancier thermostat that tallies the run time. Otherwise you have to monitor it manually.
If you’re in Chicago, the run time should be close to 24 hours a day when it’s -15F. That means that it should be close to 12 hours (50%) when the average temperature is 25F.
(Skippable explanation: the heat loss is roughly proportional to the difference between the outside temperature and 65F. So the heat required at -15F is twice the heat required at +25F. You can do the interpolation to any other temperature.)
How much of the time is your furnace running? If it’s only running 25% of the time when it’s 25F, the furnace is twice as big as it needs to be.
Would you buy a car with twice the horsepower you really need? (And even if you would, no one gets to marvel at the size of your furnace.)
The larger furnace is not less efficient in a proportionally larger house. It is only less efficient in a small house, because of short-cycling. The furnace needs to warm up fully to hit peak efficiency, and constantly going on and off does not allow it to do so. (With cast-iron heat exchangers, short-cycling can also mean that the cast iron rusts and ultimately develops holes because the condensate does not fully evaporate.)
I don’t have a reference to a paper in Physical Review Letters. But googling for “furnace oversizing” or “furnace right-sizing” will bring up many hits. For a sample, see
http://www.doityourself.com/stry/choosing-the-right-size-boiler-for-your-home
http://www.heatinghelp.com/Forum (search the forum)
(These are from a quick search, they are not necessarily the most authoritative sources.)
Cheap/flimsy isn’t the same as small. In spite of my remark about manufacturers’ profits, the price difference between (say) a 80,000 BTU furnace and a 140,000 BTU furnace is small compared to the difference between good-quality vs commodity furnace.
I don’t mean to start so many separate posts. But your software is not set up to allow post editing past a few minutes.
Here’s a verbose but delightful article on boiler sizing by Dan Holohan, a well-known authority on heating issues:
http://www.masterplumbers.com/plumbviews/2005/boiler_sizing.asp
(Incidentally, a boiler is for hot water heat or steam heat, but many of the same considerations apply.)
I’ll do some research and see what I can find on oversizing. I’m not disputing your claim necessarily, I just want to find some more scientific/testing-based backing.
Your point about condensation is interesting, but don’t most modern furnaces have non-corrosive heat exchangers? I thought aluminum or stainless or some other alloy was standard?
No, el cheapo cast iron is still standard on 80%-efficiency boilers, and the heat exchangers are thinner than they used to be 30 years ago, which helps efficiency but they develop holes faster.
A stainless steel heat exchanger is a premium item, and while aluminum-based heat exchangers exist, they are rare.
Regarding quantitative scientific studies, you may want to ask the aforementioned Dan Holohan for citations. He runs heatinghelp.com and probably has a posted e-mail address there.
If it were up to me, I would turn the heat way down during the day when few people are in the house and they are moving around and are active, and the sun is (possibly) shining. Then I would turn the heat up during the evening and the night, when people are more stationary and there is no possibility of the sun helping out. Then down a bit more when everyone has gone off to bed, and on again before people wake up in the morning. How come no one ever seems to mention that plan? It’s always On during the day,way Down at night, and that just doesn’t work for me comfort-wise. And if I’m not comfortable, the whole thing is pointless.
Not a peer-reviewed paper, and contains claims rather than hard data. But it is a PDF file, which should count for something. And it’s published by the gummint.
One problem is that paper is talking about boilers not FAG or FAE furnaces. I see what they’re saying about purge air, but they don’t quantify what these losses are. The other problem is that in the single example they show, they presuppose the efficiency but do not show how they arrived at the efficiency. I can do the same math and show the reverse is true, that small boilers are more efficient.
But it’s published by USDOE!
Seriously, I agree; I posted it partly because there was contact information on it. I haven’t been able to find a rigorous study but someone at DOE must know.
This appears to be the same confusion addressed in the published article. We all say “turn the heat up”, but the thermostat setting is not the heating rate, only the room temperature. If the sun is shining, the stat will make the boiler run less often because the sun is doing some of the boiler’s job. Thermostats do that automatically, it’s what they do.
The thing is, you control the temperature you want, not the amount of heat that is input. If your setpoint temperature for people in the house is 72 deg F, then any sun heating and body heat from moving around is automatically accounted for by the thermostat, which reads the temperature and pumps heat on when the temp exceeds the control boundaries.
So when the evening comes, sun goes down, and people are sitting more, but the set point stays at 72 deg F, then the boiler/heat pump will operate more to offset the missing heat from other sources. And when you crank up the oven and the kitchen starts getting toasty, the boiler/heat pump will operate less.