Does anyone really know if it is preferable in terms of efficiency, fuel used (and possibly cost) during cold weather to
1) Keep heating on constantly and allow thermostats to cycle on/off
2) Switch on only when needed and allow house to cool when not needed and warm up from the colder temperature
Maybe havent expressed it that well, but I'm sure you'll understand the question. Is it better to feed in small amounts of energy to keep it at a constant-ish temperature, or only use when needed with associated warming up period?
We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember mjbarnard saying something like:
I find the latter. I have my CH come on every couple of hours for half an hour and let the boiler cycle within that half hour. I find this a good solution for really cold evenings and freezing overnights. There is always somebody up and about here in the night, so there has to be heating for them. It's quite economical doing it this way.
The way I see it is that the higher the average temperature you maintain the higher the fuel bill. Since leaving the heating off for a time obviously reduces the average temperature the fuel bill will be lower but the saving may not be as great as might be thought as wwhat will actually govern the saving is the reduction in heat lost as the house cools towards ambient which might not be very much at all before it is decided to warm the house back up again.
You could look at the problem graphically. Plot inside and outside temperature together on a graph and the area between the two lines is a measure of the heat input required. The potential saving is the area between the constant temperature line and the line you would have if you turned the heating off for a period.
This question usually comes up at this time of year :-) The only real answer is that you'll have to experiment. IME, (2) is cheaper, but the saving isn't as much as you'd hope because there's a long warm-up time once it gets really cold. If you _really_ want to cut costs, forget heating the whole house and just have a fan or radiant heater on where you're sitting, but the viability of this depends on how many of you there are, how much you move around and whether you can stand arctic excursions to the loo and kitchen, not to mention a cold bedroom.
This question usually comes up at this time of year :-) The only real answer is that you'll have to experiment. IME, (2) is cheaper, but the saving isn't as much as you'd hope because there's a long warm-up time once it gets really cold. If you _really_ want to cut costs, forget heating the whole house and just have a fan or radiant heater on where you're sitting, but the viability of this depends on how many of you there are, how much you move around and whether you can stand arctic excursions to the loo and kitchen, not to mention a cold bedroom.
Chris
you could also invest in some really good thermal underwear, then one can turn the room stat down a couple of degree's and save a lot of money that way.
The answer will depend on how of the time the house is occupied.
i.e. you'll get different answers for someone cooped-up at home, who just nips out to the shops once every couple of days, compared to someone who works away from home all week and are only comes back at weekends ...
I understand there may not be a simple answer to this.
I was imagining a "typical" scenario - where when heated the house should be reasonably uniformly warm at whatever desired temperature in all relevant areas. Secondly a reasonably typical scenario where house needs to be heated early in the morning before leaving for work/ school, and from late afternoon to 10 or 11 at night.
Yep, but as has been said elsewhere, it might not save you as much as you think. Given that you have to bring the house back up to temp again when the heating comes on. Not that this isn't worth doing.
ISTR last year when this came up someone did a bit of back of the envelop calc to show that it might easily not save very much (of course rate of heat loss will be a big factor here.)
At the moment we are round much of the day, so it's just on during the day (though at a bit cooler temp than the evening) At night the stat is set for about 14C IIRC. For oen thing wife doesn't liek to much heating in the bedroom at night. But if the weather is cold enought he heating will kick in to stop it getting too cold, so it doesn't take too long to get up to temp in the morning.
The OP was looking for a "strategy" but didn't define what the goal(s) of that "strategy" are.
Cheapness, yes only heat when required but depending on the house this might not be very comfortable. If you have modern, well insulated, box that will warm up in 15 minutes or less then switching off when not required isn't much of comfort problem. On the other hand if you have a place with high thermal mass taking an hour or longer to warm up you leave the heating on.
The simple timer on/off control and basic single set point thermostat is a bit crude unless you constant tweak the thermosat and on/off button. Much better is a programmable thermosat, that can effectievly do everything automagically and you only need to manually adjust things when the normal routine changes.
Basic physics dictates that the rate of heat loss will be proportional to the heat difference between inside and out. Over time it will be proportional to the average difference. Therefore having a higher average indoor temp (e.g. heated for longer) will lose more heat.
So in cost terms you can argue that letting it cool when not needed will be cheaper. However the difficulty with this approach is that in buildings with a high thermal mass, this at best reduces comfort, and at worst means that you can't actually get the place to the desired temperature at all since it takes too long to recover from the cool periods.
You haven't thought that through. Having to have backup is closer to the reverse.
So what part of the remainder of that sentence did you not understand before you edited it out?
"the fuel bill will be lower but the saving may not be as great as might be thought as wwhat will actually govern the saving is the reduction in heat lost as the house cools towards ambient which might not be very much at all before it is decided to warm the house back up again"
So you don't think that overshoot contributes to average temperature?
Have you seen the way some competitors in mpg contests choose to drive?
I read this yesterday at about 7.30am as the temperature in my living room crept up past 17C and resolved to massage the early morning temperature sequence a bit. (Was set to 13C overnight with increases at
4.30, 5.30 and 6.30). Duly done but this morning the temperature has just crept past 17C at 9.00am.
Outside the temperature has been between -5C and -6C since 2.00am. Yesterday over the same period (and indeed for considerably longer) it was averaging a positively balmy -1C. Now considering shifting to the frost stat setting for the duration of the cold spell with the set temperature 19C. The upstairs stat can stay on its variable cycle as that should not have much trouble raising the bedroom a few degrees if downstairs is permanently hot.
Hmm, having written the above I decided to look at the graph for inside temperature and was surprised to find that even on a bitterly cold night like last night the downstairs temperature had only decayed to about 14C before the first increase kicked in at 4.30am. Perhaps all that is required is a rethink of the overnight temperatures. Upstairs already has a minimum of 16C.
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