: home heating costs 72 degrees versus 68


troutaholic
12-22-2008, 06:51 AM
Ok, on the surface it makes sense that you would save money if you reduce your thermostat to 68 degrees But why? I understand the initial cost incurred when going up to 72, but once at that established heat level, why would it cost any more? Does heat dissipate faster if warmer?

If the thermostat kicks in at the same degree drop level(70 and/or66), shouldn't the cost to increase the heat level to the desired setpoint be the same?

Hollis Uled
12-22-2008, 07:12 AM
The differential makes a big difference. Heat always moves from a warmer area to a cooler one. If those walls/windows, ceilings etc are a lot colder heat will be lost faster to those directions. Think how little your heat comes on if the outside temps are say 60 compared to 10 degrees. I look after a friends house where he keeps the temps around 45 all winter as he travels to Mexico for the winter. Surprising how little fuel he burns to keep it that way for a full season.,

cjbrown
12-22-2008, 08:09 AM
Crank those gas furnaces UP!! My natural gas stocks are lagging...............

AllenW
12-22-2008, 08:23 AM
Can't remember where I picked this up, but it seems to run with other articles I've seen, take figures as a approximate, depending on fuel costs and where you live..

Al

"A common misconception associated with thermostats is that a furnace works harder than normal to warm the space back to a comfortable temperature after the thermostat has been set back, resulting in little or no savings.

This misconception has been dispelled by years of research and numerous studies.
The fuel required to reheat a building to a comfortable temperature is roughly equal to the fuel saved as the building drops to the lower temperature.
You save fuel between the time that the temperature stabilizes at the lower level and the next time heat is needed.

So, the longer your house remains at the lower temperature, the more energy you save.
Another misconception is that the higher you raise a thermostat, the more heat the furnace will put out, or that the house will warm up faster if the thermostat is raised higher.
Furnaces put out the same amount of heat no matter how high the thermostat is set--the variable is how long it must stay on to reach the set temperature. In the winter, significant savings can be obtained by manually or automatically reducing your thermostat's temperature setting for as little as four hours per day.
These savings can be attributed to a building's heat loss in the winter, which depends greatly on the difference between the inside and outside temperatures.
For example, if you set the temperature back on your thermostat for an entire night, your energy savings will be substantial.
By turning your thermostat back 10 degrees F to 15 degrees F for 8 hours, you can save about 5% to 15% a year on your heating bill -- a savings of as much as I% for each degree if the setback period is eight hours long.
The percentage of savings from setback is greater for buildings in milder climates than for those in more severe climates.
Save 25 percent of your heating bill by turning the thermostat down from 70 to 65 degrees while awake and down to 60 or 55 degrees while sleeping or away.

It's an myth that rewarming a house after turning down the thermostat takes the same amount of heat that was saved. The truth is that the bigger the difference between the indoor and outdoor temperature, the more heat escapes your house.
Lowering the thermostat decreases the difference and you lose less heat.
Chuck Seipp, energy analyst with Arrowhead Economic Opportunity Agency, recommends keeping the thermostat turned down to within IO degrees of the original setting. Some efficiency is lost when the difference is greater than 10 degrees, he says.

A hot water faucet leaking one drip per second pours 3,120 gallons of hot water and $35 a year in energy costs down the drain. The fix is usually a cheap washer or, in newer washerless faucets, a drop-in cylinder."

MK cant log in
12-22-2008, 08:49 AM
Ok, on the surface it makes sense that you would save money if you reduce your thermostat to 68 degrees But why? I understand the initial cost incurred when going up to 72, but once at that established heat level, why would it cost any more? Does heat dissipate faster if warmer?

If the thermostat kicks in at the same degree drop level(70 and/or66), shouldn't the cost to increase the heat level to the desired setpoint be the same?


As another reply mentioned, the greater difference in temperature (Delta T in thermodynamics class if I remember right) the faster the heat transfer.

For example, if your house loses 20,000 BTU per hour at 68 degrees it might lose 25,000 BTU/hr at 72 degrees so your furnace will have to make up 25K BTU instead of 20K BTU. At 80 degrees it might increase to 40,000 BTU/hr. Its an exponential loss, not linear.

The smaller temperature difference between the house and outside temp, the slower the heat loss, and vice versa, the greater the difference, the faster the loss. The same with heat gain in the summer. My AC unit runs almost constantly when it reaches 95 degrees outside but at 85 degrees it only runs about 25% of the time.

guest
12-22-2008, 10:44 AM
If you have a heat recovery ventilator in your house you can throw all that out the window.

SwimJig
01-10-2009, 08:41 PM
Lets say my thermostat kicks the furnace on after the temp drops 5 degrees, and runs for say, 10 minutes to recover the 5 degrees of lost heat. Why would it take more fuel (money) to keep the house fluctuateing between 70 & 75 degrees as opposed to 65-70 degrees? Other than the initial longer heat time to reach the 75 degree setting, the house is looseing 5 degrees and recovering 5 degrees in either case. Unless I am missing something, a person who sets their thermostat low isn't saveing money, just living in a cold house. I'm assumeing I'm wrong, but can someone tell me why?

kman
01-10-2009, 09:42 PM
Thermal energy moves from warmer temps to colder temps. The greater the the temp difference, the faster the thermal movement..If the inside temp of your house is 75 and the outside temp is 25, you have a 50 degree difference between inside temp and outside temp.. Now if the inside temp is 65 and the outside temp is the same as before,25 degrees, we now have only a 40 degree temp difference. 10 degrees is actually quite a bit of difference. If your body was to lose or gain 10 degrees you may not be alive. Remember, the cold temps outside are not trying to get in your house, rather the heat in your house is trying to get out.

Chad
01-10-2009, 09:56 PM
Ok, on the surface it makes sense that you would save money if you reduce your thermostat to 68 degrees But why? I understand the initial cost incurred when going up to 72, but once at that established heat level, why would it cost any more? Does heat dissipate faster if warmer?

If the thermostat kicks in at the same degree drop level(70 and/or66), shouldn't the cost to increase the heat level to the desired setpoint be the same?

To summarize what someone else wrote earlier.

The higher the difference in temp from inside to outside the more energy lost. By reducing the differential you loose less energy.

#1-68 inside vs 20 outside = 48degree differential
#2-78 inside vs 20 outisde = 58 degree differential
The larger the differential the more energy lost.
This makes sense to me.

MikeF
01-10-2009, 10:50 PM
Think of the temperature differential ( inside/outsde temps) as a slope.

How fast you slide down is relative to the how steep the slope.

How fast nature tries to equalize temperature is relative to the temperature differential.

Insulation slows the equalization.

Works both ways, winter and summer.

Apple Guy
01-11-2009, 12:20 AM
Allen's quote -

"Another misconception is that the higher you raise a thermostat, the more heat the furnace will put out, or that the house will warm up faster if the thermostat is raised higher.
Furnaces put out the same amount of heat no matter how high the thermostat is set--the variable is how long it must stay on to reach the set temperature."




I want to add one caveat, a new high end modern 2 or 3 stage furnace are or can be set-up to not fire all of it's burners and have the extra one to fire for the added btus. This happens if you don't come up to your temp. after a set time from 5 to 15 minutes that can be set in increments of 5 mins. The second is set your high end thermostat to "multi stage" and if you go from 65 deg. to 70 degs the furnace will kick in the dormant burner, but if you move up the temp from 65 deg to 66 or 67 the furnace will not kick in the extra dormant burner and it will take longer to get up to your set temp. The benefits are when the burner is dormant, you get the furnace to burn longer and get into it's more efficient burning temperature for the secondary heat exchanger.

I have the high end 2 stage furnace ( 96.7 % efficient) and the high end Honeywell thermostat that gives you conventional and multi stage options and I have it set to the conventional or not multi stage to keep the furnace in the lower, longer burning mode to try to squeak the most out of the furnace and DC drive with longer and lower RPM burn times. I would only kick into the added burner mode in the morning and when I chose to turn the temp down when we would leave for 6-8 hours. Not a whole lot of energy savings, but that is the way I chose to run it. Once a month I switch it over and back to get the dormant burner a couple of cycles to keep it running right from lack of use. Allen is in the heating biz and knows about this, his statement is true to 90% of the furnace owners. I wanted to add it because more and more people are going to the 2-3 stage furnaces then use to.

mac
01-11-2009, 06:12 AM
I have the same 2-stage furnace and really appreciate the added efficiency with the cold weather and high gas prices.

What I really need is someway to hurry up global warming. It's going to be -25 in SD on Thursday.

Hollis Uled
01-11-2009, 07:29 AM
Good posts, yours too Kman except I might differ on the cold not trying to get in. When you are talking about infiltration (which for many INSULATED houses will be the major heat loss) Cold air has a lot of (effective) pressure on your house. I remember trying to help an older person save on heat, She had a porch that was closed in many years ago and was connected to her house when they removed a wall. Those windows allowed a LOT of heat loss. She was out of money to heat it by mid winter. As a temporary help, we covered those windows in cheap polythene across the whole bank of them as one piece, Sealed it with duct tape on the perimeter. In a very short while it ballooned out and was very firm,.. Next very cold day it burst away from the tape. We really couldn't keep it on. I had to spend a good part one day with some permanent and some "seal and Peel" temporary stuff it tighten enough to slow down the burst factor.

About Global warming,..most models show that as most of the globe gets warmer , most of N.America gets colder, so I wouldn't count on a balmy SD right away,...besides you guys are tough, if you weren't you'd had frozen to death years ago.....

Raybob
01-11-2009, 08:16 AM
another heat-loss item -> outside doors ...I've noticed that numerous in & out uses along w/open door talkers increases heat loss. A unheated but insulated back porch/coat-room w/3 doors between the main house and usually unheated garage or outside door sure seems to help. (think youngin's) :)

Hot Runr Guy
01-11-2009, 08:28 AM
another heat-loss item -> outside doors ...I've noticed that numerous in & out uses along w/open door talkers increases heat loss. A unheated but insulated back porch/coat-room w/2 doors between the main house and usually unheated garage or outside door sure seems to help. (think youngin's) :)
Yeah, what he said. It amazes me to this day that more homes aren't designed with an "airlock" or entry vestibule, so that the interior door never really see's a direct blast from outside. Of course, maybe most families are like mine, we use our attached garage as our primary entrance/exit. If it wasn't for those pesky people trying to save my sorry butt, I could lose the front door key.
HRG

retire55
01-11-2009, 10:03 AM
Here's a web reference that provides the formula to calculate the rate of heat transfer for any variables -
see http://hyperphysics.phy-astr.gsu.edu/Hbase/thermo/heatloss.html#c1

Using this formula, the rate of heat transfer (rate of house cooling down) with an inside temperature of 70 degrees F and an outside temperature of 28 degrees F is 707 BTU per hour. If ones drops the inside temperature to 65 degree F, the rate of heat transfer declines to 623 BTU per hour. In these calculations, I used 320 sq feet of area and a thermal resistance (R-Factor) of 19 (same numbers as in the web reference).

yarcraft91
01-11-2009, 11:04 AM
I ran numbers through a different calculation, but the conclusion is about the same. Heating the home at 72 degrees vs. 68 in my geographic region (roughly 7200 heating degree days/yr) increases the annual heating bill roughly 10%. I burned roughly $850 worth of natural gas in the furnace during the past heating season with the house at 68. I could have avoided my spouse's complaints about being cold last winter for $85.

I don't think I'll tell her.

Raybob
01-11-2009, 11:24 AM
I've heard for many years that "Each degree above 70 F can increase your heating costs by as much as 3-5% per degree" -so I just did a quick google search: . . http://www.reliant.com/en_US/Page/Shop/Public/esc_topics_achv_heat_home_shp.jsp

yarcraft91
01-11-2009, 11:41 AM
I've heard for many years that "Each degree above 70 F can increase your heating costs by as much as 3-5% per degree" -so I just did a quick google search: . . http://www.reliant.com/en_US/Page/Shop/Public/esc_topics_achv_heat_home_shp.jsp

I've heard the same rule of thumb, but "as much as" means most people can expect less (sorta like gas mileage, huh?).

The warmer the climate, the higher the % increased cost from raising inside temperature, but it's a larger percentage of a smaller number. When the outside temperature is -40 (springtime in Fargo?), the percentage difference in cost between keeping the house at 68 vs. 72 is small- less than 4%, but it's 4% of a big heating bill.

Apple Guy
01-11-2009, 11:43 AM
Like Yarcraft91, I have refused to be cold all winter for a $100 hit. I will work overtime 4 extra hours and enjoy a warmer temp.

EXCEPT there has been a riff in my world. The wife is going into pre menopause so she is turning down the Tstat this year to my chagrin. And guess what also comes with menopause??? HELLP !!!!!!!!!!!!!!!

yarcraft91
01-11-2009, 11:48 AM
Like Yarcraft91, I have alwaysed refused to be cold all winter for a $100 hit. I will work overtime 4 extra hours and enjoy a warmer temp.

EXCEPT there has been a riff in my world. The wife is going into pre menopause so she is turning down the Tstat this year to my chagrin. And guess what also comes with menopause??? HELLP !!!!!!!!!!!!!!!

Been there, done that, good luck! This, too, shall pass and she'll turn that t-stat back up. As for the rest- you're on your own, pal.

Hollis uled
01-11-2009, 12:07 PM
Yar and Imac,..I found a great equalizer to that problem is to wear a CHEAP (note cheap,expensive TOO warm) fleece PULLOVER top. (zippered ones don't seem to fit the same.) I Get mine at Wallmarts Joblots, Odd Lots etc. costs -10-15 bucks.

They are so light that I forget that I have them on. Much better than a sweater or sweat shirt IMO. I am amazed that the RANGE of comfort is better too. I can run out to the unheated workshop for a while, or jump in the car and go downtown, get out, walk down the street for a while (in all but really cold days) and go into a warm shop etc, and still feel pretty comfortable in that whole range of temps. I own enough jackets,coats sweaters etc. that would compare to Emelda Marcos shoes, but generally I wear a pullover fleece top in cool to slightly cold weather, a zip up one over top of same if cold and a nylon windbreaker over any or all if its windy. I can go out in sub zero and at least my top is nice and warm.

But a cheap pullover fleece in the house is my standard winter clothing now . ( I must have 10 of em) One in the car for if I get stuck somewhere in an emergency and I find I'm dressed too light. I even have used that in the summer for a late night /early morning chill. Generally don't need it but at times I was glad it was packed in a ziplock with the air squeezed out.

Apple Guy
01-11-2009, 12:25 PM
Good advice, I have had to wear more clothing of late because of the wife's finger. I have found what you have said to be true. You can stand more of a temp swing.

AllenW
01-11-2009, 03:35 PM
Thanks for bringing up the multi stage furnaces, I work with them so I should have caught that..ooops

Al

Texeye
01-11-2009, 06:32 PM
In the end, it is all about insulation.The object is to keep the air you have heated up, in your living space as long as possible. Most people would be far better off by spending their hard earned money on insulation. Not only is it normally cheaper than a high efficient heater, in the long run it will save more money.I would say most homes over ten years or older do not have adequate insulation. One easy check is your attic. If you can see the joists you probably need more insulation.

Here is a good place to check if you have enough insulation in your house.http://www.ornl.gov/~roofs/Zip/ZipHome.html

SteveJ
01-11-2009, 07:02 PM
In the end, it is all about insulation.The object is to keep the air you have heated up, in your living space as long as possible. Most people would be far better off by spending their hard earned money on insulation. Not only is it normally cheaper than a high efficient heater, in the long run it will save more money.I would say most homes over ten years or older do not have adequate insulation. One easy check is your attic. If you can see the joists you probably need more insulation.

Here is a good place to check if you have enough insulation in your house.http://www.ornl.gov/~roofs/Zip/ZipHome.html

The comment on most homes over ten years old not having adequate insulation probably depends on the part of the country you are in. I purchased a new home in 1985 with 6" walls, R48 in the ceiling and call casement windows with LowE glass. It was cheap to heat/cool then and would still be 23+ years later. In the 14 years I owned it I never had a gas bill over $95. We then moved from Minnesota to Atlanta and ran into high gas bills. Part was the price for natural gas and the rest was the way homes were built.

Modog
01-12-2009, 05:46 PM
#1: The outside temp is 0 degrees, and the thermostat is set at 60 degrees.

#2: The outside temp is 10 degrees, and the thermostat is set at 70 degrees.

Which scenario would consume more fuel to maintain inside temp? (Assuming all other factors are constant, ie. wind, sunshine, etc.)
Or would they be the same?

yarcraft91
01-12-2009, 05:50 PM
#1: The outside temp is 0 degrees, and the thermostat is set at 60 degrees.

#2: The outside temp is 10 degrees, and the thermostat is set at 70 degrees.

Which scenario would consume more fuel to maintain inside temp? (Assuming all other factors are constant, ie. wind, sunshine, etc.)
Or would they be the same?

The difference would be so small it would be hard to measure. In the absence of other heat sources (people, cooking, lights, etc.) the difference would approach zero.

ecj
01-12-2009, 06:37 PM
I mac guy, what furnace do you have. I have not seen a residential furnace that does not fire every burner. 2 stage furnace is usually hi and low fire gas valve but all burners are still firing just at a different btu rating. The newer high end residential furnaces now have a modulating gas valve which have more steps to the gas valve then a 2 stage furnace but still fire all burners. Maybe you have a furnace that I have not seen before. Was just curious.

Apple Guy
01-12-2009, 07:09 PM
ecj, You are right, it doesn't drop a burner. My mistake. The minute I read your post I know I posted bad info. Sorry. A friend of mine got the next size up furnace like mine and it has on more burner. I had that on my mind at the time and went with the wrong info. Sorry. I still run in 2 stage mode to open the secondary valve on the gas valve.

This is the furnace I have.

http://www.americanstandardair.com/HomeOwner/Products/Furnaces/Freedom95CR.aspx

.