Help keep me and MrLyzzyBee warm AND solvent this winter

October 19, 2008 10:23 AM

Gas Central Heating. Is it cheaper/ more economical to run the central heating on for a) a long time at a lower heat temperature or b) a shorter time at a higher heat temperature? I can't seem to get this out of Googling as all the words are so common. Note: I know it's good to have a thermostat. We will look into that - our current thermostat just turns the heating off whatever we set it to. So I just need an answer to the a) or b) bit above at the moment. Thank you! Help keep me and MrLyzzyBee both warm and solvent this winter!
posted by LyzzyBee to home & garden (13 comments total)

Setting your thermostat to a higher temperature won't make your furnace work any harder/burn more fuel, it will just have to run longer to achieve that higher temperature. It does take more energy to bring the house up to a given temp than it does to to maintain that temp, so I would set the thermostat at your comfortable minimum and raise it when necessary. I'd get that thermostat fixed/replaced asap though, as being able to automatically lower the temp when you're asleep/away can put a real dent in your heating bills.
posted by bizwank at 10:35 AM on October 19, 2008

Seconding replacing the thermostat. It's not terribly difficult, and almost all new digital ones come with instructions, complete with wire color codes. If the one you pick up doesn't have instructions, Google it and you'll find plenty.

Totally worth it.
posted by InsanePenguin at 10:39 AM on October 19, 2008

The temperature of the air coming out of your heater does not change, and a thermostat simply tells the heater to turn on at a certain room temperature, which is measured at the thermostat. So setting the thermostat to a higher temperature (say 72 rather than 68) just means it will run until the measured room temperature is 72 instead of 68, which means it runs longer and costs more.

It is more economical to run the heater as little as possible within your comfort range, which means setting your target temperature at the lowest comfortable number. The reason programmable thermostats save you money is, as previously mentioned, you can program them to set that target temperature lower when you're not home (or in bed), so the heater runs less. It is totally worth it, because remembering to manually set it down and up and down again is hard to keep up with.
posted by Lyn Never at 10:50 AM on October 19, 2008

THanks for the comments so far. So we have a dial on the front of the boiler that we can turn up or down and that's the manual thermostat, presumably. And if we have it turned down, the house won't be so warm and we'll keep the costs down.

Is that right?

BUT - is it better to have it on longer at that low temperature, or for a shorter time at a higher temperature.

We cannot mess with the automatic thermostat on the wall as a) it was installed by the previous owner and he did things like leave the back doors not screwed into the wall and b) in the UK we are not allowd to do ANY electrical work ourselves without a qualified electrician.

So - I know it's good to have the thing as low as possible, any comments about length of time having it on? We already have it pretty damn low, just to a point where we don't actually have to wear outerwear indoors...
posted by LyzzyBee at 10:56 AM on October 19, 2008

in the UK we are not allowd to do ANY electrical work ourselves without a qualified electrician

Not strictly true. You can do whatever the hell you like, but if you do significant amounts of electrical work or particularly complex jobs as DIY (and IMO replacing a thermostat wouldn't fall into that category) then you have to have it inspected by your local authority building inspectors.

Otherwise, you couldn't change a lightbulb or a plug without calling in an electrician.
posted by PeterMcDermott at 11:05 AM on October 19, 2008

OK, that makes sense though I will still ask someone more skilled than us to help with that! But thanks for the clarification. I thought that would come under the work one does have to have checked.
posted by LyzzyBee at 11:09 AM on October 19, 2008

BUT - is it better to have it on longer at that low temperature, or for a shorter time at a higher temperature.

It makes no difference, the boiler is either on or off. The longer it's on, the more fuel it will burn, the more you will pay. The temperature setting is just to tell it when to turn off.
posted by bizwank at 11:22 AM on October 19, 2008

THanks for the comments so far. So we have a dial on the front of the boiler that we can turn up or down and that's the manual thermostat, presumably. And if we have it turned down, the house won't be so warm and we'll keep the costs down.

Is that right?

BUT - is it better to have it on longer at that low temperature, or for a shorter time at a higher temperature.

As others have said, turning up the dial won't make your furnace any hotter. Your questions seems to assume that you will achieve the same room temperature but that their are two paths to that a) longer and lower, or b) shorter and higher. There is one path, that is turn on the furnace until the temperature is reached. The furnace is an on/off device (unless you have a fancy circulating hot water system in which the water temperature is set based upon the outside temperature but that is not done through your thermostat in the room but through a separate one with an outdoor sensor.) When you turn on your heat the thermostat senses whether the room temperature is below the setting - if it is the thermostat turns on the furnace until the room temperature is at the set point and then turns off the furnace. Turning up the thermostat just changes the set point. Up will use more gas, down less. Even if you have to hire an electrician to put in a programmable thermostat it will likely pay for itself within a year or so in reduced heating bills. The temperature loss to the outside (which is essentially what your furnace is matching) is proportional to the temperature difference between your inside temperature and your outside temperature.
posted by caddis at 12:31 PM on October 19, 2008

++caddis.

lower setpoint temp will result in lower costs... the temperature differential is what you are maintaining. (extrapolate to 0 temperature differential and you'll see the cost is 0.) As you raise the interior temperature, the fixed thermal resistance inside-to-outside stays the same, meaning you are losing heat at a greater rate. it has to be made up.

it's the most salient answer in the thread. (this question has a 1000 permutations on mefi!)
posted by FauxScot at 1:04 PM on October 19, 2008

OK, I think I have worked out that I was thinking a bit illogically here. Thanks everyone for the comments. I will continue to keep it on low for the time being and sort out the automatic thermostat after that.
posted by LyzzyBee at 1:36 PM on October 19, 2008

LyzzyBee's mention of a boiler makes me think that this is marginally more complicated than the standard Newton's-law-of-cooling situation caddis etal. are describing. Am I right in assuming that your heat has a central gas furnace (on/off) which heats a more or less sealed water/steam system (settable temperature) which then heats the house through a set of radiators? And you actually have two thermostats— one (which works) which controls the temperature of the water, and one (which doesn't work) which controls whether the hot water gets circulated through the radiators in order to maintain the temperature in the living space?
posted by hattifattener at 4:13 PM on October 19, 2008

I can't tell you exactly how to apply this principle to your boiler, but our new super-duper high-efficiency energy-saving (forced-air) furnace has two stages and this is supposed to be more efficient. It runs at a lower intensity (60% of full-blast, I think) for 10 minutes and if the thermostat hasn't turned it off in that time (which is rare) it will then go to full blast.
posted by winston at 7:06 PM on October 19, 2008

If you have a standard UK heating arrangement, it isn't strictly true that the temperature will always be constant, because there will be temperature controls on the radiators too, which don't work like a thermostat at all.
posted by Acheman at 4:50 AM on October 20, 2008