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

orrery

Mickey666 said:

I've installed a zoned system with TRVs and don't have a wall thermostat anywhere.

That may be OK with intelligent, linked TRVs that control the boiler. With standard TRVs you risk the boiler short-cycling and not behaving as a condensing boiler and therefore not operating efficiently.

There will always be a temperature above which you don't want any part of the heating to run and that would be the temperature you'd set the main stat to, leaving the TRVs to regulate each area individually. In addition, any reasonably  intelligent wall stat will switch into proportional mode as it approaches the set-point temperature - i.e. it will turn on for a set proportion of time, reducing as it approaches the target. The technique improves control and minimised overshoot, and ensures the boiler isn't left to run for long periods without being pushed back into condensing mode.

Cardew

Lynne_sears said:

Proof is in the energy Bill . I am upset that Martins logic says turn it off.

It is not 'Martin's' logic' it is basic physics.

This thread is 111 pages long and similar posts like yours keep appearing.

If you get cheaper bills by leaving your heating on 24/7 at any temperature you see fit  - well done. It is understandable that some people keep the heating on 24/7 because they have ventilation problems and otherwise black mould appears. etc etc etc.

MSE newsletter is read thousands/millions of people and yet again perfectly sound advice is in the latest version:

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

This is a hotly debated one. According to experts at the Energy Saving Trust, the idea it's cheaper to leave the heating on low all day is a myth. They're clear that having the heating on only when you need it is, in the long run, the best way to save energy, and therefore money. (A timer's best as your thermostat turns your heating on and off to keep your home at the temperature you set.)

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 (how much will depend on how good your insulation is). The Energy Saving Trust says if you're keeping the heating on all day you're losing energy all day, so it's better to heat your home only when you need it.

So why get upset when Martin(or his staff) publish sound advice for all readers - even if that doesn't apparently agree with your theory and the laws of thermodynamics? Do you not think that if you keep your house at, say, 19C and it is say, 5C outside, that heat is not leaking from your house?

For those who argue (against the law of physics) that it takes more energy to bring the house back up to temperature than keep it at a constant temperature ask yourself the question posed many times in this thread:

If you were leaving your house for two years would you keep the house heated at a constant temperature - because it is cheaper than switching the heating off and having to heat the house when you return?

If leaving it for one year - same question?

A month? A week? A day? 12 hours? 6 hours? at what point does the law of physics not apply?

 

richardc1983

The thing that doesn’t seem to be mentioned here is that less heat leaks out keeping it at 19c than heating to 22c then shutting it off between timings. I keep mine at 19c then up to 20c in the evenings for comfort this for me in my 1930s 2 bed house is cheaper than running it a higher comfort temp as if i turned it off between periods the house would drop to about 17c then if I expected to feel warm at 20c set temp the house would still feel cold so 22c is needed to make the house feel warm enough. This uses more gas as the thermostat runs the boiler harder and because everything is cold it takes longer to come up to temperature.

A modulating boiler will work harder the larger the difference in room temp and set temp, plus the lower your flow temp keeps the boiler even more efficient. 19c  24\7 keeps the flow temp at approx 30c turning off fully then setting to come at 22c it will spend an hour at 75c then the rest of the 6 hours at about 52c whilst modulated down it’s using more gas than when I boost to 20c when it will tick over at about 34c. Rads feel cool but the house is warm, we have not noticed increased gas usage but the house is comfortable all the time, 

Cardew

richardc1983 said:

The thing that doesn’t seem to be mentioned here is that less heat leaks out keeping it at 19c than heating to 22c then shutting it off between timings.

At the risk of another argument, that is a meaningless statement unless you include timings, and heat loss properties of the building

Rather than having it set to a constant 19c; you will lose less heat if you have it set to 19c and switch off heating for a period of time. That period can be 1 minute, 1 hour, 1 day, 1 month, 1 year and it doesn't matter about the heat loss properties of the building.

I admire your detailed knowledge of gas consumption rates, at all different boiler water temperatures for your boiler, during all periods, and for all levels of modulation.

Apparently these figures don’t vary for changes in outside temperatures and it doesn’t seem to matter if the boiler is in condensing mode or not. (I assume you have a condensing boiler)

You have a 1930s 2 bed house; would your method work for all the thousands of readers of the newsletter with different style/size of property, and those who, apparently misguidedly, believe the Energy Saving Trust and countless other technical publications who give the advice shown in the Newsletter.

richardc1983

Cardew said:

richardc1983 said:

The thing that doesn’t seem to be mentioned here is that less heat leaks out keeping it at 19c than heating to 22c then shutting it off between timings.

At the risk of another argument, that is a meaningless statement unless you include timings, and heat loss properties of the building

Rather than having it set to a constant 19c; you will lose less heat if you have it set to 19c and switch off heating for a period of time. That period can be 1 minute, 1 hour, 1 day, 1 month, 1 year and it doesn't matter about the heat loss properties of the building.

I'm referring specically to thos who turn off fully and then run at a higher comfort temp to those that run 24/7 at a lower temp. 

2010

Obvious thing to do is take a meter reading, set the thermometer to required temp and run it non stop for 28 days, then take a reading.
The following 28 days switch it on and off as needed and take another reading, then compare the two.

roddydogs

Please stop resurrecting this hoary old thread.

coffeehound

orrery said:
In addition, any reasonably  intelligent wall stat will switch into proportional mode as it approaches the set-point temperature - i.e. it will turn on for a set proportion of time, reducing as it approaches the target. The technique improves control and minimised overshoot, and ensures the boiler isn't left to run for long periods without being pushed back into condensing mode.

Genuine question:  does frequently switching the boiler on and off really increase efficiency?  Since it has to go through multiple re-lights, wouldn't that be a low-efficiency phase?  Also when it is shut off, and the pump stops, isn't there going to be heat lost from the HX that doesn't make it into the water.  Continuously running at a relatively low temperature with the boiler relighting infrequently to top up the water circuit temperature 'feels like' it should be more efficient overall as all the heat from the burn goes into the water, and no cycles are interrupted.  I'd be interested to know the details on these situations.

Talldave

Modern boilers have pump overrun, which keeps water circulating for some time after the burner has been switched off.

matelodave

2010 said:

Obvious thing to do is take a meter reading, set the thermometer to required temp and run it non stop for 28 days, then take a reading.
The following 28 days switch it on and off as needed and take another reading, then compare the two.

you also need to take lots of daytime and nighttime temperature readings to correlate consumption with temperatures