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

Sea_Shell

Ultrasonic said:

richardc1983 said:

Ultrasonic said:

This may have been posted earlier in this thread but another post today made me find the following recent advice from Octopus advising setting combi-boiler heating flow temperature to 55°C:

https://octopus.energy/blog/winter-workout-gas-saving-tips/

Other advice is in line with what I actually do re. not unnecessarily heating rooms not being used, or the house at times it's not needed.

That’s the recommended maximum it should be set to for the boiler to give you the efficiency it was rated at. The lower you can put it the better. So try lower and find the point at which your home remains comfortable. Condensing starts at 55c. 

I had understood that getting the return temperature below 55°C was beneficial in terms of condensing occurring, which is why I've dropped the flow temperature setting on my boiler. I think it's important not to overplay the very modest differences this makes though. Going by that graph dropping the flow temperature from my previous 70°C to 55°C is only likely to increase efficiency by about 5 percentage points (from about 87% to 92%). If I were to drop the temperature further to get the return temperature to 40°C or so efficiency would only increase one or two more percentage points.

As far as I'm concerned, MUCH bigger savings are to me made by people reducing how much they use their heating, through reducing peak temperatures (aim to not be cold rather than to actively feel warm), and not wasting heat on rooms or at times when it's not needed. (I know you take a different approach to the latter but I do believe you could reduce you energy use if you did more of this - at least overnight.)

I agree.  And not just on energy.   Unless you've already cut your household spending to the bone in ALL areas, then you can probably make more significant savings elsewhere.

1 less takeaway a week, will no doubt save a lot more in ££ than turning the return flow of your boiler down!

richardc1983

I love how dismissive you are Sea_shell, there are people running their boilers really inefficiently at max output. This is a money saving page and it’s a bit more than a price of a takeaway. For us it’s about £25 a month in gas by running at the cooler flow temps. For some people that is probably the choice between a weekly food shop at a budget place or having the heating on, some folk don’t have the luxury of takeaways. 

QrizB

richardc1983 said:

For us it’s about £25 a month in gas by running at the cooler flow temps.

Hold on a minute. You stated:

My gas usage was 1264kwh for the month of February.

That's roughly £50-worth of gas. For you to have saved £25 by running lower flow temps, your boiler efficiency must've improved from 65% to 97%. But the chart you posted shows ~85% efficiency even with a 100C return temp, and 95% with a 35C return temp.

Reducing from 100C to 35C will give an efficiency improvement of 10%, so a saving of around £5/month.

richardc1983

That also includes running at 18/19c constant and not high bursts of heat (e.g 23c) on timed periods and using night set back. I find it amazing how you are tearing apart everything I say. This is down to individuals to trial and see what it does for them. Our previous months were higher and quite a bit higher than £5 a month saving. I've said all along it's about more than just turning the flow temp down. 

Ultrasonic

richardc1983 said:

I love how dismissive you are Sea_shell, there are people running their boilers really inefficiently at max output. This is a money saving page and it’s a bit more than a price of a takeaway. For us it’s about £25 a month in gas by running at the cooler flow temps. For some people that is probably the choice between a weekly food shop at a budget place or having the heating on, some folk don’t have the luxury of takeaways. 

Is the comment in bold referring to the cost saving you're claiming from running your boiler at a lower flow temperature? For the ~5% increase in efficiency I may get in my case I'd need to have a monthly bill of £500 just for gas usage to make a saving of £25. There isn't scope for much more than a 5% increase, and like @QrizB I don't believe you're saving this much purely down to boiler efficiency improvements.

Yes improving boiler efficiency is absolutely worth people doing but I think it's important to be realistic about how significant the potential differences are.

QrizB

richardc1983 said:

... I've said all along it's about more than just turning the flow temp down. 

Then perhaps your statement:

richardc1983 said:

For us it’s about £25 a month in gas by running at the cooler flow temps.

... was poorly-phrased?

This thread is about myth-busting, and you can't bust myths with anecdotes; it needs reliable data. Data that can't withstand challenge isn't reliable.

Ultrasonic

Cross-posted above - I do wish this forum had pop-ups when new messages are posted whilst I'm typing like many others do!

richardc1983

QrizB said:

richardc1983 said:

... I've said all along it's about more than just turning the flow temp down. 

Then perhaps your statement:

richardc1983 said:

For us it’s about £25 a month in gas by running at the cooler flow temps.

... was poorly-phrased?

I could have worded better but in my earlier posts I've referred to cooler flow temps and cooler overall running temps for comfort on the thermostat. 

It's also important to note the efficiency of the cooler flow temps is about the efficiency level from the energy recovered from the flu temperature. Turning down your flow temp also uses less gas overall even if your boiler wasnt condensing you would save by turning it down. 

The graph specifically refers to condensing mode efficiency of the boiler. Look at it separately with lower flow temp comes less gas usage, how much you'll save depends on your setup and how you use it. 

JohnSwift10

I decided to turn my boiler radiator temperature from 60 C to 50 C and it took 1 and a half hours longer to get up to the temperature of my thermostat this morning.

My heating comes on at 07:45 and the boiler gets switched off when the room temperature reaches 21 deg C.

This normally takes until about 09:00 then the boiler switches on and off to maintain this temperature until 23:30.

Today that took until 10:30.

So have I saved any gas having my boiler continuously on for 1 and a half hours longer?

Same if I go out at night for 3 hours and switch the heating off at 18:00 and on when I come in at 21:00.
Although no gas is being used between these times the total gas used from 21:00 to 23:30 is about the same as what is used from 18:00 to 23:30 if the heating is still switched on.

It may save gas if the heating is switched off for a day but in my experience switching it of for 2 or 3 hours during the day saves nothing.
At present my heating is on for 15 hours 45 minutes a day and my gas usage is on average between 42 and 55 kWh a day.

The most used in one day was 70 kWh and the least 45 kWh since the start of the year.

All this info is from my smart meter readings.

I have also, since I bought this house 31 years ago, a 3 bed semi, reduced my gas usage from a high one year of 24,000 kWh to last year which was 14,100 kWh by increasing insulation and replacing my inefficient gas warm air heating with a combi and radiators. 

richardc1983

JohnSwift10 said:

I decided to turn my boiler radiator temperature from 60 C to 50 C and it took 1 and a half hours longer to get up to the temperature of my thermostat this morning.

My heating comes on at 07:45 and the boiler gets switched off when the room temperature reaches 21 deg C.

This normally takes until about 09:00 then the boiler switches on and off to maintain this temperature until 23:30.

Today that took until 10:30.

So have I saved any gas having my boiler continuously on for 1 and a half hours longer?

Same if I go out at night for 3 hours and switch the heating off at 18:00 and on when I come in at 21:00.
Although no gas is being used between these times the total gas used from 21:00 to 23:30 is about the same as what is used from 18:00 to 23:30 if the heating is still switched on.

It may save gas if the heating is switched off for a day but in my experience switching it of for 2 or 3 hours during the day saves nothing.
At present my heating is on for 15 hours 45 minutes a day and my gas usage is on average between 42 and 55 kWh a day.

The most used in one day was 70 kWh and the least 45 kWh since the start of the year.

All this info is from my smart meter readings.

I have also, since I bought this house 31 years ago, a 3 bed semi, reduced my gas usage from a high one year of 24,000 kWh to last year which was 14,100 kWh by increasing insulation and replacing my inefficient gas warm air heating with a combi and radiators. 

Sounds like you have already made substantial changes and savings so may not work any better for you. It's suggested that when you lower your flow temp you also lower your normal comfort setting and use night setback so there is less of a swing between temps. This means the system is quicker to recover. E.g for us we would have comfort at 22/23c if running at say 60/70c and then it would just be OFF overnight and house would drop to say 16c. Now we run at 18c over night or when it would normally be OFF and then comfort temp is say 19-19.5c. 

EVery house is different sounds good what you've already managed to save. Again there is no harm in experimenting and trying.