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So, is it better to keep CH on constantly with thermostat low?

(19 Posts)
WitchesTit Mon 05-Nov-12 10:55:50

We moved house in the summer to an old house with old style boiler and hot water tank. Now it's colder we've just started to have the heating on. (It got down to 12 last night ds's room).

We've been talking to some friends who have same who say its more economical to keep the central heating switched on, and use the thermostat to keep the house at an ambient temperature rather than what we are doing at the moment, keeping the central heating switched off all the time (the separate hot water thingy is on for 30 minutes morning and evening) but turned on for a bit when we can't stand the cold anymore.

I have to say I'd love it to be a nice 16 or 17 degrees all day as I'm at home being pregnant and with a 2yo ds and i don't want him to be freezing at nighttime.
But DP says it must cost more to keep the heating on and he can't see the point of it.

Which do you think is economically better and would the difference be big enough to excuse suffering enduring cold temps through the winter?

crazypaving Mon 05-Nov-12 11:06:34

I've heard the same so will watch with interest to see what the consensus is

PigletJohn Mon 05-Nov-12 15:15:11

leaving the boiler on low will make it more comfortable.

However for economy, heat loss is directly proportional to temperature difference x time.

So if the inside of the house is 10 degrees warmer than the outide for 10 hours, it will lose twice as much heat as if it is 10 degrees warmer for five hours.

And if it is 20 degrees warmer than outside it will lose twice as much heat, in the same number of hours, that it loses if it is 10 degrees warmer.

Note that I said "20 degrees warmer than outside" which is not the same as "heated to 20 degrees." It is the temperature difference between inside and out that causes the heat loss.

For comfort, I would suggest turning the thermostat down to, say, 15C while you are in bed or out of the house. Unless the nights are very cold, a well insulated house will not lose enough heat for the boiler to come on much, if at all. You can get a programmable room stat which allows you to set different temperatures for different times of day and different days of the week, this tends to be more comfortable and more economical than constantly fiddling with the temperature.

Modern condensing boilers run more economically ticking over at 60C than if they are hotter and keep turning off and on.

PeggyCarter Mon 05-Nov-12 15:18:37

Message withdrawn at poster's request.

FuckityFuckFuck Mon 05-Nov-12 15:22:19

I've been told that as well, so I'm giving it a go at the minute. something to do with less energy needed to keep the temp constant instead of having to heat up a freezing cold house to the right temp once/twice a day

We shall see

WitchesTit Mon 05-Nov-12 15:30:24

Ah PigletJohn I knew I could count on you! The maths bit of your response is a bit confuddling to me but my pregnant brain is working slowly through it.

PigletJohn Mon 05-Nov-12 15:40:57


the rate of heat loss will vary depending on the size of the home and how well insulated, but the Second law of thermodynamics still applies

PigletJohn Mon 05-Nov-12 15:43:38


For simplicity, you might find it easier to think of it like this


OhYoubadbadKitten Mon 05-Nov-12 15:44:33

Agree with pigletjohn on this one smile

Pigletjohn, can you recommend a good programmable thermostat? At the moment our on/off times is controlled by the boiler and its a bit of a pain.

PigletJohn Mon 05-Nov-12 16:04:27

I am currently using a Danfoss one, but I have already bought an ACL Drayton which is considered to be better, but some people complain they are too complicated as they try to learn how fast your house heats up and predict what to do.

The Honeywell CM range are said to be very good as well. I would avoid a wireless one as it gives two more levels of potential failure.

this should be pretty good. Read the reviews.

WitchesTit Mon 05-Nov-12 16:08:21

I think my brian just exploded

fussychica Mon 05-Nov-12 16:13:12

We have done this for years and find it far more comfortable and no more expensive.

OhYoubadbadKitten Mon 05-Nov-12 18:36:15

Thanks smile I had a look at that one but it doesn't seem to do the full 7 days. this one seems to do a good job though I think?

NotMostPeople Mon 05-Nov-12 18:41:50

We just had this conversation at the weekend. Dh was quite horrified that I wasn't putting the heating on during the day as it was 'just me' at home, he said there's no way he would do the same if he was the SAHP. We've set all our rooms to 20 degrees since Saturday and I've been keeping an eye on the boiler. It's actually on very little as once the temperature is reached it just tops it up every now and then when it drops and then switches off again once 20 has been reached.

If in doubt read your meter, keep the heating on for two days and take a second reading. Then do the same again with turning it off and on so you can compare the usage.

MrsMiniversCharlady Mon 05-Nov-12 18:57:59

Poor Brian sad

Iggly Mon 05-Nov-12 19:00:04

We have ours set to come on when it drops below 19C which at the moment it rarely does. And stick another layer on.

Being too cold isn't good for vulnerable people (ill/elderly/young children).

WillowinGloves Mon 05-Nov-12 19:04:46

My mum experimented with this a couple of years back - she had always done the 'turn it off/put it on' routine but tried instead to keep it on but turn the thermostat up and down. She's in an old end-of-terrace house which can't have cavity wall insulation but has loft insulation. She compared usages over the two winters and found no difference and says she never needs heating on too high with this system to stay warm.

PigletJohn Mon 05-Nov-12 19:05:17


looks like the equivalent would be the Honeywell CM907, should be a similar price but is not on ScrewyouFix. I agree being able to set days with different patterns is useful. I find 18C is OK during the day, for some reason I feel colder at night.

Horstmann is usually a first-class company for timers so I expect theirs is good.

Remember that with a programmable stat, you turn the boiler CH timer (if there is one) to 24hrs on, and the stat will turn it down (effectively off) when not required. Usually 12C is the anti-frost setting.

OhYoubadbadKitten Mon 05-Nov-12 19:49:51

Good to hear they have a good rep smile thank you.

Remember for those of you experimenting with seeing whether you do better to have it on all the time or on/off to pick two days (incl nights) with similar outdoor temps, else it will be a bit of a rubbish experiment!

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