Energy myth-busting: Is it cheaper to have heating on all day?

Cardew

However well meaning, IMO this thread is in danger of spreading the wrong message to the majority of readers seeking advice on keeping energy costs as low as possible.

This statement is correct!

Should I leave the heating on low all day even when I'm out, or turn it up only when I need it?

According to leading energy experts at the Energy Saving Trust, as well as British Gas, the idea that it's cheaper to leave the heating on low all day is a myth. They're clear that you'll save energy, and therefore money, by only having the heating on when it's required. (Using a timer's best, because your thermostat is designed to turn your heating on and off to keep your home at the temperature you set it.)
The key thing to understand here is that it's all about the total amount of energy required to heat your home.
It's a given that a certain amount of energy is constantly leaking out of your home (though exactly how much will depend on how good your insulation is). So the Energy Saving Trust says if you're keeping the heating on all day you're losing energy all day - and therefore it's better to heat your home only when you need it.

The longer your heating is off, the more money you save!

Whenever this statement is made we get posts advancing scenarios where it doesn't apply to a particular set of circumstances in a particular property.

All of these cases appear to be based on assumptions that savings in keeping a boiler in condensing mode are so great that they outweigh any other consideration. Yet they can't quantify those savings or indeed know exactly when a boiler is in condensing mode.

I have a new boiler with all the gizmos, including weather compensation, yet nowhere in the instructions, and talking to the design engineers at the factory, does it recommend keeping the heating on 24/7.

The basis for the advocates of heating constantly appears to be the assumption that heating a cold house means the boiler will not be in 'condensing mode'. Not true as far as I am concerned! A boiler modulates its output.

Blackbeard_of_Perranporth

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I let my 24/7 thermostatic time switch dictate when my heating is on high or low. Current consumption on Gas is 11,200 kWh per year, down 1,500 kWh this year as we had wall insulation added last December!


I know what it costs, no condensate in my house and BoPsie keeps her tootsie warm!

[Deleted User]

Cardew wrote: »

However well meaning, IMO this thread is in danger of spreading the wrong message to the majority of readers seeking advice on keeping energy costs as low as possible.

This statement is correct!

The longer your heating is off, the more money you save!

Yes, but the point is that it's not proportional. The reason is that the temperature rise and fall times are not symmetrical:



When the heating switches off, the temperature falls only slowly because there is a large amount of heat stored in the fabric of the building, but when the heating switches back on, the rooms quickly warm up because the boiler can deliver heat faster than the building loses it.

This asymmetry means that the mean temperature is not proportional to the duty cycle of the timer.

With the heating switched off for 29% of the day (00:30 - 7:30) I measure a gas saving of about 8%. Calculating the savings, I get about 10% which is still nowhere near 29%.

The problem gets complicated further because a cooler mean temperature with the heating timed may induce the occupants to turn the stat up higher, further reducing the savings.

I run my heating timed, but leaving it on is not as expensive as it might appear at first sight.

System

Google: ON/OFF thermostats; TPI thermostats and Opentherm thermostats. If moneysaving is the aim, then the only way to objectively monitor your CH system is to use a usage meter such as Loop; Smappee or NorthQ.

Cardew

jack_pott wrote: »

Y

I run my heating timed, but leaving it on is not as expensive as it might appear at first sight.

Agreed.

Your scenario(understandably) is referring to a 24 hour cycle with heating only off at night - for 29% of the 24 hour day - and the saving is a not inconsiderable 8%(over that 29% period) by your calculations.

However many people are out working during the day and a typical weekday scenario might be heating on from 06:30 to 08:00 and 16:00 to 23:00, thus heating off for 69% of the 24 hour day.

Obviously the savings will depend on the property. However given the thrust of some posts on this thread, people could be forgiven for thinking that leaving the heating on 24/7 would be cheaper - and it ain't!

molerat

Energy myth-busting: Is it cheaper to have heating on all day?

Do I really care ? The heating is on when I feel I need it to be on, usually 24/7 from late Nov - early March at a cost of less than £1 per day extra. Compare that to the price of 20 cigs or a pint in the local !

lstar337

Cardew wrote: »

I have a new boiler with all the gizmos, including weather compensation, yet nowhere in the instructions, and talking to the design engineers at the factory, does it recommend keeping the heating on 24/7.

Nobody mentions the wear either.

My boiler is on 2 hours a day (via timer), though maybe not the whole two hours if the house is already warm. But how long is a boiler running if the heating is on 24/7? In a poorly insulated house it could be on a lot of those 24 hours.

Who's boiler is going to wear out sooner?

Any what about the electrical usage? Yeah the pump isn't drawing tons of current, but it is drawing some.

The 24/7 heating argument fails in so many areas, and simple gas costs aren't even the whole story!

lstar337

molerat wrote: »

Energy myth-busting: Is it cheaper to have heating on all day?

Do I really care ? The heating is on when I feel I need it to be on, usually 24/7 from late Nov - early March at a cost of less than £1 per day extra. Compare that to the price of 20 cigs or a pint in the local !

It must take a long time going into each topic you don't care about to let us all know. I just ignore the topics I'm not interested in, it's so much easier.

victor2

A majority of people will probably go along with the common-sense approach that the heating will cost you more if it is on than if it is off.
Sure, if you want, and can afford, to maintain a certain level of comfort, you can run the heating for longer hours. Or if you are prepared to invest a significant amount of time, effort and money, you can make your heating system efficient for your particular circumstances, so that it can have a very small financial impact for running longer hours.
Nobody will tell you they went on holiday, leaving their house empty for a week and left the heating on at 20 degrees for the duration, so that they came back to a warm house, and it cost them no more than switching the heating off for a week.
Still, this discussion has been going on for over 5 years and is approaching 1000 posts. Anybody care to summarise it?

lstar337

victor2 wrote: »

Anybody care to summarise it?

Sure.

The longer your heating is on, the more it will cost. :money:

I think that about sums it up.