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All night central heating?

Burra Maluca
Mother Tree

Joined: Apr 03, 2010
Posts: 5011
Location: Portugal Zone 9 Mediterranean Climate
    
189
Someone on another forum asked if it was more efficient in extremely cold weather to keep central heating on 'tick over' all night or to heat the house from cold in the morning.  I have a feeling that 'tick over all night' is going to be more efficient, but does anyone have any sold information I can pass on?


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Joined: Dec 15, 2010
Posts: 105
Burra Maluca wrote:
Someone on another forum asked if it was more efficient in extremely cold weather to keep central heating on 'tick over' all night or to heat the house from cold in the morning.  I have a feeling that 'tick over all night' is going to be more efficient, but does anyone have any sold information I can pass on?


It is as long as they do not lower it too much. 5 to 7 degrees F usually nets money in your pocket including the warm up the next morning.


Professor of Thermal and Electrical Engineering, Welding/metallurgy: Licenses: PE license, Mechanical license Variety of other "certifications" from industry groups such as Refrigeration Service Engineers Society http://www.rses.org/, ASHRE http://www.ashrae.org/ Ect.
paul wheaton
steward

Joined: Apr 01, 2005
Posts: 15416
Location: missoula, montana (zone 4)
    ∞
This my ten cent graph of what is in my head.

The red represents house temp over a 24 hour period.  Midnight to midnight.  Warm things up in the morning and in the evening. 

The blue represents energy used to get that house temp.

The peaks in the second graph represent the same temp in the first graph. 

When you turn the thermostat down, there is zero energy used for a while.  Then there is a much smaller amount of energy used to maintain the lower temp. 

Then, when you turn the thermostat up, a lot of energy is used to get the whole house back up to the higher temp. 

In the end, there is energy savings, but it isn't as much as you might hope. 

Supposing for a moment that it takes 100 units of energy to  maintain the higher temp all day, and it takes 50 units of energy to maintain the lower tempt all day, you might think that turning the thermostat down to the lower temp for 18 hours a day (3/4 of the day) would bring you down to 60 to 65 units of energy a day.  But those spikes in energy use to get the temps back up use a lot of energy units.  So your total energy use will probably end up around 90 units of energy per day.  So you saved energy - just not as much as you you might think/hope.

(all this depends on dozens of factors, so this is all a lot of averaging and generalizing and a heavy dose of utter fiction - but this is what is in my head)

This is why I think there are way bigger savings to be had by keeping the temp low all the time.





[Thumbnail for night-heat.png]


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Joined: Dec 15, 2010
Posts: 105
Well said Paul,

If a person is home very little but at the same time each day, the set back can save you some bucks wile providing comfort while you are there.

Set your stat to the lowest "I am totally happy" temp you can, if you have periods of over 5 hours, set the lower set point about 5 degrees below that and you will save energy. If you go lower than that, while you will save energy in heating the air, allowing the walls, furniture and such cool down too much will use all your savings to warm the space back up.

You might see a lot of claims, I would estimate the savings between 2 and 10 dollars a month so in most folks cases, the automatic thermostat will pay for itself in about 2 to 5 years.

The same goal can be done by setting it yourself, just do not take it to extremes.

A vast majority of folks would indeed be better off to turn it as low as they can enjoy and then sit with a comfy blanket or snuggle with a friend instead of sitting on opposite ends of the sofa!
Jami McBride
volunteer

Joined: Aug 29, 2009
Posts: 1782
    
  11
I agree - low all the time for central heating and then add spot specific heating to warm up 'areas' during their use in the day time.  Such things as room heaters, heating pads, and such.
                                


Joined: Jan 13, 2011
Posts: 12
I'll throw one out, a flat line in the dead of winter (one temp that is comfortable) works very well, only because of demand. Keep things warm when you need them that way, it's a comfort thing ONLY. And when you consider heating and cooling all your furnishings when it's frigid, don't they hold/emit heat? If your O.K. with being chilly after kneeling in the snow all day, you are a better man than I.
Whatever,,,,what about a timer on your hot water? I'll bet you don't need that as much. Key is how are you getting it, a timer (in the majority of cases) will work (fuel usage wise) to save the most.
Heat can vary spring and fall, you can jump the heat up and down and still be comfortable (depending on you) but cold times are what they are, cold.
S'up to you what works.
Len Ovens
pollinator

Joined: Aug 26, 2010
Posts: 1302
Location: Vancouver Island
    
  16
shaneaaron wrote:
I'll throw one out, a flat line in the dead of winter (one temp that is comfortable) works very well, only because of demand. Keep things warm when you need them that way, it's a comfort thing ONLY. And when you consider heating and cooling all your furnishings when it's frigid, don't they hold/emit heat? If your O.K. with being chilly after kneeling in the snow all day, you are a better man than I.

We have timerstats one to a room. For bed rooms 8am till 7pm there is no one in them and we let the temp drop. In the evening the temp goes to a warmer but still cool sleeping temp, then in the morning it goes up to "comfortable to get out of bed" for a bit... this helps us to wake up too. I work outside and find the the house temp can be quite cool and still feel very warm when I first get in, but when I sit down a bit, I need it warmer. With timerstats you have to set the times earlier than you need so the room has a chance to get to the temp you desire before you need it and of course the heat can shut off a bit before you are finished with it too.

Note: It doesn't get as cold here as some places, our average minimum is around freezing with 10 below that being unusual, but happens once in a while.... really cold is -14C (1949) but that was a long time ago. Anyway, even though the cold setting on our timerstats is set to 12C, the coldest it ever seems to get inside is 15C, except downstairs at 12C, but no heat besides computers and misc electronics... and the earth it sits in. Our high setting is 19 or 20C (normal in most homes is 22C think 72F) and our sleep setting is 18 or 19C at the years coldest and as low as 17C in the shoulder months (Oct,Nov,Mar,Apr) then it gets set to vacation for the summer (12C... means off).


Whatever,,,,what about a timer on your hot water? I'll bet you don't need that as much. Key is how are you getting it, a timer (in the majority of cases) will work (fuel usage wise) to save the most.


We do that too. What we don't do but really works well, is to schedule hot water use to minimize the amount of time the water heater needs to be on. Ours is electric and so could be super insulated which might save just as much as turning it off at night.... gas heaters have to have air flow to feed the fire and exhaust to take fumes away... so with the tube up the center taking heat out all the time, extra insulation on the out side doesn't do near as much. IMO the insulation it comes with doesn't do that much because of the core heat losses.
bob smith


Joined: Nov 30, 2011
Posts: 1
The reason lowering the thermostat at night saves money is because you are lowering the temperature differential. As you lower the temperature differential, you lower the energy transfer rate. In other words, the hotter the house is the winter, the FASTER it will lose that heat to the outside. It doesn't cost you more to heat the house back up in the morning, unless you have some old inefficient 2 stage heat pump. but it still should be less energy than keeping the house warmer during the night.

Just remember, the bigger the difference in temps, the FASTER the energy transfer.
paul wheaton
steward

Joined: Apr 01, 2005
Posts: 15416
Location: missoula, montana (zone 4)
    ∞
Your point about the differential is spot on.

And .... I stand by my point that it takes much more energy to warm a home 15 degrees than 2 degrees.

The strategy of setting the thermostat to 70 for an hour in the morning and for four hours in the evening , seems like it would cut 70% off of the heat bill. I think it will cut only 10% to 15% off of the heat bill. So there are savings, but I think the "heat the person, not the whole house" strategy has a far greater reward.

Brad Davies
volunteer

Joined: Sep 22, 2011
Posts: 212
Location: Clarkston, MI
    
    8
paul wheaton wrote:Your point about the differential is spot on.

And .... I stand by my point that it takes much more energy to warm a home 15 degrees than 2 degrees.

The strategy of setting the thermostat to 70 for an hour in the morning and for four hours in the evening , seems like it would cut 70% off of the heat bill. I think it will cut only 10% to 15% off of the heat bill. So there are savings, but I think the "heat the person, not the whole house" strategy has a far greater reward.



I agree with both of these points based on my experience in my house. I've been in my house for 2 winters, going on the third.

The first winter I was manually adjusting the thermostat, down to 55ish at night up to 63-65 when someone was home bills were approx $80, $115, $130 for Nov, Dec, Jan. Near the end of Jan I installed a wood burning fireplace insert with a blower and used that to play the game "don't let the furnace kick on" My next gas bill was $80 for Feb, $40 for march. Feb is just about as cold as Jan here, March similar to Nov.

The second winter I was promised a "whole bunch of wood to keep you warm." When my friend finally came through on this the wood he dropped off was a bunch of water logged pine. Needless to say it was no good for keeping me warm. I was however given a programable thermostat at about the same time. I figured I wouldn't see much difference since I had been doing it manually but as it turned out it saved me ~$50/month. Temp is set at 55 at night, warms up to 60 for 2 hours in the morning when everyone is waking up, goes back down to 55 while we are at work. Then warms up to 63 right before I get home from work. Sometimes I would turn it up to 66 if I was getting complaints from certain girlfriends, but now they know that when it's winter you shouldn't be wearing a T-shirt and complaining about the cold.

So wood burning stove saved ~$50/month
Programable thermostat saved ~$50/month

This year I have a decent stock pile of wood and still have the thermostat set the same way. I'll keep track of my results but so far so good, turned the furnace on for the first time last week. It only seems to run when I am at work because when I wake up the house temp is still above the min threshold of 55.


SE, MI, Zone 5b "Opportunity is missed by most people because it is dressed in overalls and looks like work."
~Thomas Edison
Jami McBride
volunteer

Joined: Aug 29, 2009
Posts: 1782
    
  11
I cut my electric bill by $100 a month just by doing two things:
1. burning one fire when the sun went down each night, lasted about 3 hours, usually done by 8:30-9pm.
2. and replacing my very old fridge (because it died) with a new energy saver model.

I couldn't believe the instant savings.

The fire was in a standard fireplace (no efficiency there) but was just feet away from the thermostat keeping the central heating off for hours.
We would then retire to our cool bedrooms for the night. Saving $100 during the winter months was really a blessing. I'm a believer in room heating over central heating.
                        


Joined: Apr 25, 2010
Posts: 64
good thread, I've played around with these things too and my findings/ feeling on it is... I keep the oil heating on 24/7 with the thermostat set at 18C this is through the day and night during late autumn. I find this does not really be warm enough by Dec and find that I have to raise the temp to 19C at night, I might still get away with 18C during the day, but in the early evening say 6pm - 10pm it will set at 20C .... Surprisingly when it gets really cold outside these temps don't seem to be warm enough indoors, its almost as though the set temps loose at least 2C ! I've heard an explaination which made sense at the time.

So when it gets cold and strong winds blow I find the temp needs to be raised by 1 - 2C ... however, I also have a woodburning stove and when its lit in the hard winter it keeps the thermostat from coming on most of the time, and yet the oil is there to keep things above freezing through the night. There might well be a small saving by letting the house cool right down, however I feel its better to have a steady heat on keeping the damp air at bay, plus the added comfort should you be home.
Last winter, many folks in my area were caught out with freezing temps day and night and came home from work or awakened to frozen water pipes, another reason to keep the heat on 24/7. Just my long 2p worth.

Cheers
Fred Morgan
steward

Joined: Sep 29, 2009
Posts: 972
Location: Northern Zone, Costa Rica - 200 to 300 meters Tropical Humid Rainforest
    
  12
So, why would anyone want to make their home warmer?

(being a smart alec here in the tropics... sorry : )


Sustainable Plantations and Agroforestry in Costa Rica
                      


Joined: Dec 02, 2011
Posts: 6
Location: New Hampshire
Last winter I put in programmable thermostats. I also put in some redneck insulation in the living room and put bubble wrap on my daughter's bedroom window. The thermostats are great- when I get up the house is warm and the heat is already back off. My (always cold) wife loved the insulation at her desk immediately. My daughter didn't like the bubble wrap because it made her room too hot.

This year I've already got the sliding door panels up and I've bubble wrapped the whole upstairs- if our room with the thermostat has matching extra insulation, her room won't get overheated. I'm still playing with ideas (and looking for time) for making a solar air heater to feed through a south facing window.

Now that I've finally started reading more here instead of just thinking "yeah, I really ought to get over to check out Permies," I read Paul's 87% article and watched the beginning of the video. Today the kids' Christmas presesnts for Mommy came in the mail: a pet bed warmer, swing arm lamp and IR bulb. Now maybe I can set the ground floor cooler in the evenings.
kent smith


Joined: Sep 05, 2010
Posts: 211
Location: Pennsylvania
Just a question and idea. Where do you figure in the thermal mass of the house and its contents? I don't have numbers, but it seems like the mass of the house works better here if it is maintained rather that the hours it takes to reheat the mass.
kent


Kent
                      


Joined: Dec 02, 2011
Posts: 6
Location: New Hampshire
I'm heating air for a short time. I get up at 5:30 and I'm out the door at 6:30. We're gone till 5:00 and then the kids, lights, TV and cooking add to the heating. After 8:00 the kids are under blankets and we're usually down by 11:00. Outside of those times I just don't want the pipes to freeze.

Now in my next house, the one with the solar radiant heating and a masonry stove, I'll worry about thermal mass.
Don McLean


Joined: Dec 30, 2011
Posts: 6
Location: UK
Not sure that's resolved - would be really nice to!

A quick search I did seems to support it IS better to turn heating off when you don't want it, & on when you do, (AND HIGHLY recommends very programmable heating programmers, many time periods at different temperatures etc). Because, as others have pointed out here, the higher the temperature inside, the greater the heat loss to the outside.
For example:
http://www.grist.org/article/advanced-degrees
Dear Umbra,
Many of my friends are environmentally minded and do lots of things to try to have a smaller carbon footprint. Yet when I tell people I turn my heat down when I leave the house even for an hour or two, and that I turn it down to 50 at night, they say, "I thought it takes more energy to reheat the house than to keep it at a constant temperature." Please clarify. If it is better to turn the heat down, then there is a LOT of room for education on this topic, as even many people in the environmental community are confused.

ANSWER
Let's say a typical, nice heat setting is 68 Fahrenheit while at home, 58 at night or while away. (Your 50 is probably lower than most people will try, but bravo to you.) The heater will save fuel as it falls to 58, and expend about the same amount of fuel as it rises back to 68. Therefore, these two transitional phases cancel each other out. And while the heater is set at 58, for as long as it is set at 58, it is merrily saving fuel (aka energy, money, and the planet). Because as we all know, it takes more heat to keep a house at 68 than at 58. Overall, then, fuel is saved.
To bulk up this answer a little bit and remind us all that insulation and sealing the house are important aspects of keeping ourselves, but not the planet, warm, let's discuss air-movement dynamics briefly. Remember, air lives a life of heat equality. Hot air wants to rush out and share the heat with nearby cold air until all air is the same temperature. This happens, as fervid readers may recall, through the processes of convection, radiation, and conduction. The stack effect is an example of convection: Hot air in a building not only rises, but is of higher pressure. As it rises, it pushes against any cracks in the ceiling or roof, escapes, and leaves a low-pressure area at the bottom of the house. The cold air rushes in to the low-pressure area, and must in turn be heated.
Our heaters are fighting an incessant battle on our behalf, warming all the new air. If we are not there to be warmed, or are sleeping under a cozy duvet, we can turn down the thermostat. Programmable thermostats are very helpful and quite cheap.
I repeat: Reheating uses less energy than keeping it hot while you're gone. No organization -- reputable or disreputable -- disagrees with this advice. To quote the EERE, "This misconception has been dispelled by years of research and numerous studies."

One link quoted supporting this view in one the replies might have clinched it
“If you want to really nerd out over this here is most recent, over-instrumented research:
http://www.homeenergy.org/article_full.php?id=566&art ...”
but frustratingly, won't work for me!

ALSO: extracts from the EERE advice:
http://www.energysavers.gov/your_home/space_heating_cooling/index.cfm/mytopic=12720
“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. In fact, as soon as your house drops below its normal temperature, it will lose energy to the surrounding environment more slowly. The lower the interior temperature, the slower the heat loss. So the longer your house remains at the lower temperature, the more energy you save, because your house has lost less energy than it would have at the higher temperature. The same concept applies to raising your thermostat setting in the summer; a higher interior temperature will slow the flow of heat into your house, saving energy on air conditioning.”

[Unfortunately I am then lost, when EERE advise states:
Limitations For Homes With Heat Pumps, Electric Resistance Heating, Steam Heat, And Radiant Floor Heating
Programmable thermostats are generally not recommended for heat pumps. In its cooling mode, a heat pump operates like an air conditioner, so turning up the thermostat (either manually or with a programmable thermostat) will save energy and money. But when a heat pump is in its heating mode, setting back its thermostat can cause the unit to operate inefficiently, thereby cancelling out any savings achieved by lowering the temperature setting. Maintaining a moderate setting is the most cost-effective practice. Recently, however, some companies have begun selling specially designed programmable thermostats for heat pumps, which make setting back the thermostat cost effective. These thermostats typically use special algorithms to minimize the use of backup electric resistance heat systems.]

ALSO: advice from the UK Government's Energy Savings Trust:
http://www.energysavingtrust.org.uk/In-your-home/Heating-and-hot-water/Thermostats-and-controls
“Programmer or time control
This will automatically switch your heating off when you’re not at home, or when you can do without it, such as when you’re in bed.
Programmers allow you to set ‘on’ and ‘off’ time periods. Most models will let you set the central heating and domestic hot water to go on and off at different times. There may also be manual overrides. Check that the timer on the programmer is correct before you set your programmes. You may also need to adjust it when the clocks change.
Choose a cold evening and time how long it takes for your house to warm up from cold to a comfortable temperature – this is the warm-up time. Then turn the heating off completely and time how long it takes for the house to start to get uncomfortably cold – this is the cool-down time.
You can now set your timers including the warm up and cool down time. So, for example, you can make sure that the heating goes on with a warm-up time before you wake up and turns off before you leave the house. If you insulate your home, it will warm up more quickly and cool down more slowly, so you’ll save money on heating.”

Please note however:
the EST advise says allow for the warm-up and cool down times.
Clearly, if your house / heating system is such that the warm-up period is longer than a period you leave then return to your house, then you can't turn the heating off (and expect the house to return to a comfortable temperature when you want it to). You'd need to turn the thermostat down to whatever the heating system can recover from, when you leave.
If this is the case, then we are dealing with “extreme” cold and / or relatively poor house construction (or possibly high heat expectation).

I think Paul's point:
“And .... I stand by my point that it takes much more energy to warm a home 15 degrees than 2 degrees.”
is certainly true, but the logic wrong, since you've been paying (using energy) to keep your home that extra 13 degrees warmer.

HOWEVER:
(I am a home energy advisor in the UK, so have this discussion quite often) I do meet some people who claim they have tested this and found that they use less energy keeping their house on a mid-temp “tick over” while they are out, then boosting it up when they are in, rather than letting the house go “cold” (I am assuming not freezing).
I can only accept what they say, though it does not fit with what I can justify to myself, nor what “official” guidance seems to be, both in the UK and US.

Other considerations:
Paul is no doubt aware of Ianto Evans' thermal benches / beds and the like – heating furniture (rather than the surrounding air) seems a more sensible way to go, ESPECIALLY when burning wood, because the most efficient burn is a very hot burn, so the deal there is to store and moderate the heat (which massive furniture allows).
Mass furniture is unlikely to be acceptable in most modern (i.e. light-weight homes, where I suspect load-bearing capacity is a limiting factor)

Obviously we don't want our homes to freeze (burst water pipes). Modern heating programmers should include a frost setting, which will prevent indoor freezing - clearly sensible.

And yes (of course):
it is far better to only heat those areas of the house where you are (i.e. not “spare / guest bedrooms...”),
and, more extreme, but I think entirely logical, Paul's personal heating (rather than space heating), e.g. as simple as a blanket on a couch, as per your great “how I saved 87%..." article

Most of us in Europe have got used to very cheap heating, mainly from natural gas which is now getting less cheap, so I think the days of central heating (i.e., in my opinion heating under-used areas of a house) are numbered. In my childhood (I'm approaching 50), my family, who I wouldn't describe as poor, had just one heated room (in addition to the kitchen, which was warm while cooking was happening). I htink this was normal.
So in winter, we were mostly in the (one) heated room. I didn't spend too much time in my bedroom in deep winter, which could get ice on (the inside of) the windows.
Bodies are likely to radiate around 100watts / person, so a few people in one room begins to make a significant heating impact.
paul wheaton
steward

Joined: Apr 01, 2005
Posts: 15416
Location: missoula, montana (zone 4)
    ∞
And so it would seem that I need to explain this yet again: by turning the heat down at night or while at work, you DO save money. Just not nearly as much as you think you might.

So, 1 hour in the morning and 4 hours in the evening is five hours out of 24. About 20%. That means the heat will be set to a lower temperature about 80% of the time.

So people might think that they are going to save about 70% or, under the right conditions, the full 80%.

I think the savings are typically going to be more like 10% to 20%. And, of course, it depends on a LOT of factors.

If we are talking about a house that is poorly insulated and the outside temperature is 62 degrees, and the thermostat gets lowered to 60 at night and runs at 70 while people are in the house .... then I do think people will save a lot of money doing this.



Don McLean


Joined: Dec 30, 2011
Posts: 6
Location: UK
OK, thanks for clarifying Paul.
Christopher de Vidal


Joined: Nov 17, 2010
Posts: 100
Confirmation that you can in fact save money. The topic is cooling but the principle is the same.
http://michaelbluejay.com/electricity/myths.html
Kevin EarthSoul


Joined: Jan 17, 2014
Posts: 92
    
    3
paul wheaton wrote:Your point about the differential is spot on.

And .... I stand by my point that it takes much more energy to warm a home 15 degrees than 2 degrees.

The strategy of setting the thermostat to 70 for an hour in the morning and for four hours in the evening , seems like it would cut 70% off of the heat bill. I think it will cut only 10% to 15% off of the heat bill. So there are savings, but I think the "heat the person, not the whole house" strategy has a far greater reward.



One interesting way to "heat the person, not the house" is to be naked when using radiant heating, including passive-solar heated thermal mass or a masonry stove. Radiant heat is line-of-sight, whatever is exposed to the radiant body is heated. Radiant heat works efficiently by heating the bodies in the room, without significantly elevating air temperatures. Your air temperature could be 60 degrees, but perfectly comfortable, because a radiant body is putting out infrared rays to warm your skin directly.

The down-side, of course, is that 60 degree air is cooling your skin with convective and evaporative cooling. You can reduce this by limiting air-flow. It's a trade-off. The best of both worlds, is a warm bench (like some rocket stove designs), or using a thermal mass like a heated brick or water-bottle, bundled with you under some covers. Once your body's core temperature is up, skin cooling isn't as chilling.


Kevin EarthSoul (real, legal name)
Omaha, NE
allen lumley
pollinator

Joined: Mar 16, 2012
Posts: 3042
Location: Northern New York Zone4-5 the OUTER 'RONDACs percip 36''
    
  48
Kevin EarthSoul :I agree with everything you said and only want to add that there is an inverse Square rule in radiant heat in that if you are toasty warm
at 4 ft away from your Radiant heat source , you will be warmish at 8' and unable to feel the heat at 16', at that range if you are not sitting on the end of
your Thermal Mass you will be cold ! For the Craft ! Big AL !


Success has a Thousand Fathers , Failure is an Orphan

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