Central Heating

[Jasandjules]

My OH was told by a heating engineer that leaving your central heating on 24/7 was more efficient because it doesn't have to heat up water from cold each time. I think this is rubbish and it must be cheaper to only run the CH half the day rather than all the time.

Who is right?

[Simpo Two]

Jasandjules said:

My OH was told by a heating engineer that leaving your central heating on 24/7 was more efficient because it doesn't have to heat up water from cold each time.

So heating a house for 24 hours uses less energy than heating it for 12?

Extrapolate that and I can heat it all year for nothing...

[miniman]

Simpo Two said:

Jasandjules said:

My OH was told by a heating engineer that leaving your central heating on 24/7 was more efficient because it doesn't have to heat up water from cold each time.

So heating a house for 24 hours uses less energy than heating it for 12?

Extrapolate that and I can heat it all year for nothing...

Well it seems at least plausible that is cheaper to keep heating a house every hour or so from 19deg to 20deg than to heat it from maybe 10deg to 20deg twice a day... what we need here is

[jaybkay]

Jasandjules said:

My OH was told by a heating engineer that leaving your central heating on 24/7 was more efficient because it doesn't have to heat up water from cold each time. I think this is rubbish and it must be cheaper to only run the CH half the day rather than all the time.

Who is right?

I would suggest another heating engineer, this one is an idiot.

You heat your house because it's cold - the larger the temperature difference between inside and outside the more heat will be lost (no matter how good the insulation).

Hence a warmer house house will lose more heat than a cooler house - and keeping it warm costs more money than heating it when required.

The only heating system that is slightly unusual is inslab water heating with an air sourced heat pump. The heat pump is more efficient during the day (as it's warmer) and the energy is stored in the slab - hence these should be operated during the day in winter even if the house is warm enough.
All other heating systems - use them when it's cold.

[Jasandjules]

miniman said:

Well it seems at least plausible that is cheaper to keep heating a house every hour or so from 19deg to 20deg than to heat it from maybe 10deg to 20deg twice a day...

Yes, IIRC from my A Levels the specific heat capacity of water is something like 4200 j/kg/k sooo to heat 1kg of water 1 degree = 4200j BUT if it is already warm then it won't take as much to heat it!?!?

It's not heating the house that bothers me, the actual thermostat is only set around 19c and the house is always warm (too hot for me really, but the OH complains it is cold!), I just don't like having a boiler on all night long when the thermostat gets set to 15c or so. Saying that, I don't like it on all day either!

[Deva Link]

It must also depend on how well insulated the house is and how over-rated the boiler is.

In very cold weather our boiler runs pretty well all the time. So turning it off for 6.5 hours at night obviously saves gas.