Turn thermostat down?

Shrug...you really really dont know what you are missing. The woman can keep you satisfied till the day you die..which would probably be a week from next Thursday, given her sex drive.....and skills....
But then...
Gunner
"IMHO, some people here give Jeff far more attention than he deserves, but obviously craves. The most appropriate response, and perhaps the cruelest, IMO, is to simply killfile and ignore him. An alternative, if you must, would be to post the same standard reply to his every post, listing the manifold reasons why he ought to be ignored. Just my $0.02 worth."
Reply to
Gunner Asch
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When I am working the house cools off considerably at night and the next day and I have to fire the wood stove hotter than its efficient range to make up in the evening. When I am home all day I keep it warmer with about the same amount of fuel.
OTOH if I fire it normally to recover there is an obvious and considerable savings from allowing the temperature to drop for a day or two, as during holiday trips or when measuring the cooling and recovery rates.
Exact numbers are difficult, outdoor temperature changes constantly and internally the living space and basement (where the stove is) act like two loosely coupled thermal masses that cool at different rates. I think the house loses between 2% and 3% of the in-out difference per hour, substantially through infiltration which I don't want to reduce below what it is now.
jsw
Reply to
Jim Wilkins
Did the old standing pilot type furnaces tend to draw about the same current from one model to another to turn the burner on? I always thought it was clever getting a bit of heat via resistance to 'anticipate' when to turn off the burner.
Wes
Reply to
Wes
On Thu, 29 Oct 2009 20:39:27 -0700, the infamous pyotr filipivich scrawled the following:
Ayup. If any of my short list of girlfriends ever had control of the thermostat, I could bop around the house naked without a care for warmth. I was still hot. (No, not like that. Well, OK, that, too, but I meant the "I-feel-like-I'm-in-Hawaii-on-the-beach" warm.) It's a major reason I never got married. Common sense prevailed.
God, that was a meanass thing to do with male/female thermostats.
Reply to
Larry Jaques
The anticpators have an adjustment to match it to the furnace controls in question. Standard install checkout procedure is to measure the current, set the anticipator accordingly. That goes for the old standing pilot models as well as the modern microprocessor controlled versions.
Wes wrote:
Reply to
RoyJ
80% are hardly known for "sucking every BTU".
Reply to
Stormin Mormon
Granted that the 80% is less than the 92% units. But the **WEIGHTED** average stack temperature is much less than the older versions. Every short fire of the gas starts with the heat exchanger at ambient plus no more than a couple of degrees. Stack doesn't even get warm to the touch for half of the burn time in moderate weather. Hard to argue with that.
This also argues to the point that a temperature setback may not produce the fuel savings one might expect.
Storm> 80% are hardly known for "sucking every BTU".
Reply to
RoyJ
Right. But the integrated savings over time will be around half (without doing the math) of what one would have if the temperature of the house actually dropped to its final temperature and stayed there for a long time.
In other words, if the house temp keeps dropping through the day to, say, 55 deg F, and then you set the thermostat back up to your normal temperature of 70, the whole cycle is one of loss from the thermal mass, then restoration of the heat stored in the thermal mass. If your house is well-insulated, you wind up with half of the savings (slightly more; it's a calculus problem and the physics involve exponential decay, but averages will do for this discussion) you'd have if you either left the thermostat set at 55 for a couple of days, or if you had a lightly-built house with poor insulation and the temperature dropped quickly when you turned down the thermostat.
According to DOE (and I've seen that information before), the savings resulting from shutting off the furnace over a short period of time are quite small, even on a per-hour basis, because the mean temperature of the house is a lot higher than its temperature when you come home. They say that, on the average, lowering the temperature 10 - 15 deg during the workday, and lowering it again to some unspecified lower temp while you sleep at night, saves, typically, 10% of your heating bill.
Just as an example, say you saved 10 cents/hour when the temperature of the house remains at 55 over several days. But if you let it drop to 55 and then immediately turn up the thermostat to 70, you only save 5 cents/hour. And you have to wait for the house to heat up.
And here's a more telling example. Say the temperature outside is 50 deg, your normal house temperature is 68 deg., and your house is well-insulated and contains a lot of masonry, plaster walls, and other stuff with high thermal mass. You shut off the thermostat completely when you leave for work in the morning. When you come home, you turn it back up. The temperature in the house is 60 at that time. I think everyone can see that the savings due to the mean temperature differential is quite small. But many people are going to think that, because the furnace was off all day, they're saving a day's worth of fuel. Not.
If your furnace is *off*, the thermal mass is supplying 100% of the heat to the outside.
Right.
Right.
Yes, but a much smaller one than most people would think, since their furnace was off for a whole day.
Right. So it's 25% less heat loss than you have at your normal temperature, even though the temperature inside the house dropped to 50 deg. But most houses don't lose heat that quickly. As a practical matter, you're only gaining around half of what some people would expect by letting the temperature drop to 50 deg and then heating the house back up.
Without getting into the math or the other routes for heat transfer, the 2% is the point. You need to let the house stabilize at the lower temperature before you're getting the kind of savings that most people think they should get.
Reply to
Ed Huntress
No, it's dead on, and based on a lot of actual experiments.
But he explained the wrong problem. He explained a theoretical thermodynamics problem. The question is whether the savings would be worth it if you only shut off the furnace for a relatively short time. And the answer is, unless you live in a lightly-built and underinsulated trailer, probably not.
Again, you're talking about a vacuum-bottle experiment. The question is whether the savings are worth coming back to a 50 deg house.
Approximately 8% of homes.
All of this is very nice for armchair philosophizing, Dan, but you have to know the actual *values* involved in the practical problem to know whether they're significant issues, in terms of your monthly heating bill. DOE has done the work, and I've shown what their actual experiments show. The savings are quite small in a typical house unless you leave the furnace off, or the temperature set low, for a long enough period for the STABILIZED temperature to be maintained for a significant portion of the total cycle.
Thermal mass works against you, by extending the ramping-down and -up portions of the cycle. Likewise, insulation.
Reply to
Ed Huntress
I've lost track of what you're saying is "right" or "wrong." It's a fact that your savings are much lower than many would expect when you simply let the temperature drop to some particular temperature and then start heating the house up again, as you would if you turned the furnace off when you left in the morning and then turned it back on when you got home.
It's another fact that the savings become significant when the lowest inside temperature prevails for most of the cycle time, whether it's because the house has reached outside temperature or because you simply set the thermostat down to some temperature above outside temperature.
Physics was my best subject, too, Don. I'm aware of the physics involved. There even was a time when I could do the equations without batting an eye. Now, I let my thumbs rule. d8-) The question concerns whether the saving is enough to make it worthwhile, not whether you can calculate the exponential decay and the integrated temperature differential and show some numerical value for the savings. Again, it's much less than most people expect.
Reply to
Ed Huntress
As I said, I'm aware of the physics, Don. But the questions, which have gone all around the barn, are about whether it's worth it. And the answer is that it's much more worthwhile if your periods of turning the furnace off (or the thermostat 'way down) are quite long.
DOE addressed the question accurately: if you have two periods of reduced heat per day -- the time you're at work and the time you're sleeping at night -- you'll typically save 10%. That's a figure that's been tested and reported for decades.
Most people think that shutting off their furnace for four hours should save four hours worth of fuel. It doesn't. If the temperature keeps dropping until you turn the furnace back on, you save the equivalent of roughly two hours of fuel, not four hours.
And another way to look at it is whether shutting off the furnace 12 times per day, for an hour each time, is equivalent in terms of savings to shutting it off one time for 12 hours. The answer is, no; it probably is on the order of 50% of the savings you get by shutting it off once for 12 hours.
The DOE's tests specifically addressed some common misconceptions. Both in terms of the misconceptions over the physics and in terms of misconceptions about actual savings, they were quite right.
Reply to
Ed Huntress
Hers or yours? ;-)
Reply to
IanM
That's as good as any generalization. Savings vary a lot with how much the homeowner sets back and for what percentage of the time. The length of each period is only relevant if it is small or comparable to the time constant of the enclosure. If the period is short enough that the space can only cool 5 degrees, then lowering the setpoint more than that has no effect or benefit.
But the assertion about not saving anything until the house is stabilized at the lower temp is wrong, and the stuff about cycling thermal mass requiring net energy is also wrong.
When these studies were done, 10% savings was far from trivial. Houses are *much* more energy-efficient now than they were 30 years ago.
Reply to
Don Foreman
I should have said "anything significant." Somehow significance stuck in my mind throughout that discussion.
I don't know who said that, but it wasn't me. Or if I did, then I misspoke.
Just to make sure we agree here: If you read what DOE actually says, it's perfectly accurate. They don't get into thermal masses or hypothetical examples. They're talking about real savings, based both on theory and, more importantly, on real tests run over a period of decades.
Reply to
Ed Huntress
I don't know which DOE study you refer to here since there were several, but I have no quarrel with findings based on actual data. Honeywell did their own studies with similar findings.
Precis of findings: How much does a setback stat save? It depends. Are the savings significant? Maybe. 10% of not much is hardly any. 10% of a whole bunch is some. Buy a Honeywell Chronotherm. Your family deserves the best.
Some gov't studies are almost laughable when they wander off into the weeds trying to offer an impressive technical explanation of what the data says and why, which more often is really the writer's attempt to impress by verbose technobabble obfuscation. It's well known in contract research labs that the gov't wants big thick reports for their research buck. Hell, the proposals alone sometimes look like phonebooks. It's widely suspected that nobody actually reads these reports, they just weigh them and assign a grade.
Makes me think of a notorious DOH or OSHA study that spent 3/4 mil finding that pigshit is slick. (Safety issues in pig farms or something like that).
Reply to
Don Foreman
That probably was a report about Chicago's Grant Park in 1968.
Reply to
Ed Huntress
You need to improve your reading comprehension. The question was
"Is it energy saving to turn the thermostat down, when leaving the house?"
It was not whether the savings were worthwhile. Or whether a 50 degree house is comfortable. Incidentally the problem can not be accurately described by lump constants. The electrical analogy is a transmission line, not a capacitor.
Dan
Reply to
dcaster
Right. So the question was not whether it was worth doing, but whether one could calculate some reduction in total joules of energy by working it out with a calculator.
Save your pedantry, Dan. It's not illuminating. It's just annoying.
Reply to
Ed Huntress
Well everyone else was answering the question that Stormy asked. You are the only one that decided to ignore the question and answer what you wanted to talk about. Which explains why you could not understand why so many intelligent people disagreed with you. And to be pedantic, the question was not about calculating the amount of reduction. There are way too many variables to do that.
Dan
Reply to
dcaster
Pfffht. Go correct a kid's homework or something.
Reply to
Ed Huntress

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