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Wow, this is a complex one. Back in the UK, I designed and installed my own central heating system in my first house. I borrowed a book from the library (we're talking pre-internet here) and calculated the surface areas and R values for each external surface in each room. From that, and allowing for some losses (draughts and leaks) I was able to calculate the radiator size I needed for each room.
So, each house is different, surface area, construction materials, how well is it sealed ...
Then, of course, you have weather conditions. Energy loss is based on the above and the temperature difference. The warmer inside and the colder outside means more energy loss. Wind has a big impact (hence the concept of wind chill); still air will convect warm air around your house away, but wind "snatches" it away. Wind outside your house also represents a pressure difference, so sucking air out where there are leaks or pushing cold air in.
As an eco-freek, I have a very well insulated house (even though it's over 50 years old) which is heated with a ground source heat pump (geothermal system), so it doesn't take a lot of energy to heat, even though I'm in Canada (we've had temperatures below -20c and wind chills that just hurt this week!) I've met people with houses so well insulated (probably straw bale) that a hair dryer could heat the whole house in winter!
One last note when it comes to this stuff: People and animals are all sources of heat. Even a couch potato throws out a few kilowatts and someone who is active, a lot more. A large dog is quite the heat source.
Isn't physics interesting?!!!
Life is like a s**t sandwich; the more bread you have, the less s**t you eat.
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I've met a few folks with super-efficient homes, pretty much always custom-built. Plenty of them use passive solar heating. One in particular not only doesn't need any other energy for heating(in fact their problem even in a harsh winter is too much heat).
The "hair dryer" comment was about two different individuals who have retro-fitted normal houses.
Although we're almost certainly further south than you (not many people realise that southern Ontario is about level with northern Spain and further south than San Francisco!), our climate is very hot in summer and very cold in winter. Typical late January/early February daily maximum temperatures are about -6 to -8, but it can get much colder. Monday or Tuesday morning driving to work, it was -23. At those temperatures your snot freezes in your nose and your nose hairs become stiff!
Life is like a s**t sandwich; the more bread you have, the less s**t you eat.
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House or apartment ?
In my condo (10 y.o construction), I do not heat that much; my neighbors do not like cold, so I take advantage of it.
At my girlfriend apartment, an older apartment, she has to heat extensively in winter (and she do not like cold) with 3 sides of the apartment exposed.
One thing, I have large bay windows in the living room; and in Winter, I prefer keeping the curtains closed as an extra insulation.
I'd rather be phishing!
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I just leave the indoor thermostat around the 21 mark, but would certainly expect to have it on when 10 degrees outside.
I guess insulation is good to stop heat loss through the floor and walls and things, but how are you supposed to keep the air fresh? Never understood that. Bearing in mind we all breathe out water vapour the whole time without fresh air from outside it's going to get stuffy.
For that reason I sometimes opt for the extremely ungreen and expensive version of heating on with windows open.
Regards,
Rob Philpott.
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Heat recovery ventilators!
I have one (installed myself) which includes a whole-house hepa-filter. I cut the "to house" line into the return duct of our forced air HVAC system and a hole on the back wall for the "to outside" line.
It works by having a contraflow heat exchanger, so in winter warm air from the house exchanges heat with cold air from outside. In summer, the cool (air conditioned) house air pre-conditions the warm, moist air from outside. The heat exchanger also collects and sends condensation to a drain, although winter air in Canada is normally very dry anyway (unless you're in Vancouver!)
Life is like a s**t sandwich; the more bread you have, the less s**t you eat.
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I live in a converted barn - very thick walls of Yorkshire Stone. No cavity insulation at all. It's lovely and toasty - the Aga helps (horrible in summer, we have to switch the Aga off)
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I turned mine on this year when it snowed for 12 hours straight on 12/31. Things got a little chilly, since my place has only R-7 rated walls. Until that cold snap, I'd been running a pair of oil filled radiators on medium setting, which kept the place at around 65°F. The snow didn't stick much, but it hasn't snowed in Bullhead City in 40+ years.
Will Rogers never met me.
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Munchies_Matt wrote: ...when do you need to turn the heating on?
When the inside temperature falls below 65 F.
"One man's wage rise is another man's price increase." - Harold Wilson
"Fireproof doesn't mean the fire will never come. It means when the fire comes that you will be able to withstand it." - Michael Simmons
"You can easily judge the character of a man by how he treats those who can do nothing for him." - James D. Miles
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We have most of the home thermostats set at 64 F. 
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Munchies_Matt wrote: when do you need to turn the heating on?
When my wife says it's time.
Only half joking there since I tend to just put on a sweatshirt when the temp drops and can work when the house drops to 13 or so. (sorry...used to Fahrenheit.) That's the day-time temp we have set on our thermostat.
That said, I think there is a cumulative effect so that oustside temp isn't only factor. If it's been warm for several days it takes a couple of days for the inside temp to drop low enough that heat comes on during the day. (It's +2c here now and that's as warm as it's been for a few weeks so the gas meter has been spinning faster than I like)
There may be another difference. My experience is that many homes in the UK (London, Scotland) and Europe (France) are "cozier". In the US we tend to like expanses of space (e.g. the room I am in has a 20 foot...er 6meter ceiling), which is less energy efficient.
cat fud heer
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Munchies_Matt wrote: when do you need to turn the heating on?
When the base temp outside is -12 degrees F 
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This is something I have been dealing with in my house since I moved in 5 years ago. I don't even want to know how much it cost the previous owners, as most of the house did not have any insulation, the heat supply duct work was in shambles, and it seemed the doors / windows had been fitted by someone half drunk.
I am obsessive about finding heat loss in the house (yea on the really cold nights I walk around with a laser thermometer looking for cold spots).
All stuff you don't notice in the middle of Summer (the time of year I bought the house). Though I will say finding, fixing and improving the house has been great fun!
Common sense is admitting there is cause and effect and that you can exert some control over what you understand.
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Munchies_Matt wrote: their economy would have just tanked.
No, because they would still have demanded that taxpayers in England bail them out.
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They would have had to to go to the IMF, they wouldn't even have had EU membership signed off yet. It would have been a disaster.
What both the US and UK govs should do is buy the oil off their producers at say 60$ a barrel, and stock pile it. After Suadia gives up playing its games and the proce goes back to 75$ it can be sold for a profit.
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Munchies_Matt wrote: They would have had to to go to the IMF
I doubt it. Even with a "yes" vote we would have had to support them for a good many years while they attempted to get control of their affairs.
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When you say "we" ... are you an expatriate Briton or an Anglophile Frenchman?
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Munchies_Matt wrote: After Suadia gives up playing its games and the proce goes back to 75$
What makes you think that it would go up again? And where did the number 75 come from?
I've heard 75, 80 and 100, but those are not fair prices; they are limits.
Bastard Programmer from Hell 
If you can't read my code, try converting it here[^]
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