My gas usage is still the same

david1946

I had turned down the temperature of the water flowing round the radiators from 67 deg C to 60 deg C and notice that for the first 15 minutes my heating is on in the morning  07:45 - 08:00 ( I have a smart meter and I get the details from data.n3rgy.com) I am using approx 0.6kW less gas (0.509 M3 - 0.458 M3) the heating is on for longer before it reaches the room thermostat set temperature.

During the day when the boiler comes on to maintain the temperature it takes slightly longer to reach the set temperature and at the end of the day the total usage is still the same as when the water temperature was higher.

In conclusion the only way to use less gas is to have the thermostat set lower and not the temperature of the water flowing round the radiators.

So I have turned the water temperature back to its previous setting and have the house reaching its set temperature quicker.

QrizB

Turning the flow temperature down from 67C to 60C will only save a tiny amount.

The chart everyone uses looks like this (this one is in Fahrenheit, I will convert for you):

67C is 153F; on that chart it gives a boiler efficiency of slightly over 86%.

60C is 140F; on that chart, efficiency is a bit more over 86%.

You really need to get your flow temp below 130F / 55C before you get into the "fuel savings" section of the chart. 120F / 50C will see your efficiency rise to around 88%, 100F / 40C gets you to about 94%.

[Deleted User]

QrizB said:

Turning the flow temperature down from 67C to 60C will only save a tiny amount.

The chart everyone uses looks like this (this one is in Fahrenheit, I will convert for you):

67C is 153F; on that chart it gives a boiler efficiency of slightly over 86%.

60C is 140F; on that chart, efficiency is a bit more over 86%.

You really need to get your flow temp below 130F / 55C before you get into the "fuel savings" section of the chart. 120F / 50C will see your efficiency rise to around 88%, 100F / 40C gets you to about 94%.

I've followed the advice given (probably by yourself and one or two others in this forum) re turning down the flow temperature.  Now set at 50C.and has been for the best part of a week.  Certainly the comfort feels different (as per the OP) to what it was when it was set at 60/65 but I think I am overall I using less although the temperature has been realtively mild in the NE recently.  We shall see what the long term numbers (and comfort) feel like.  Thermostat set at 18C in the morning and a little higher at 18.5C in the evening.  Not shivering too much brrr.

jamei305

Surely that chart is showing the inlet temperature, not the output temperature which is what the setting on the boiler will control. The inlet temp will be the temperature after the heated water has cycled around the radiators and gone back to the boiler, so will depend on the total output of the radiators and several other factors.

BUFF

Yes, it is the return temp.




Assuming a typical 20C differential between flow & return then 75C flow gets you 55C return which (depending upon a few other variables like air pressure) is likely to be just into the condensing zone & on that image ~87% efficiency.
If you drop the flow to 65C, so return of 45C, then your efficiency jumps to ~ 92%
If you drop the flow further to 60C, so return of 40C, then your efficiency increases to ~ 94%.
The difference between a flow temp of 65C & 60C is only ~2% which could easily mean that the difference in energy consumption on an individual day due to the change could be easily overshadowed by a difference in the weather conditions or perhaps even meter tolerances, changes in calorific value of the gas etc. 

Running lower temps also tends to be better for the system.

[Deleted User]

Quote: Assuming a typical 20C differential between flow & return then 75C flow gets you 55C return Unquote

And therein lies the challenge. Over the years, a large number of condensing boilers have been added to existing systems designed for a higher boiler flow temperature and a 10C return differential. I doubt that many homeowners have considered the need for bigger radiators or have made any attempts to re-balance their systems. There have been a number of studies which have concluded that most homes have boilers that rarely condense.

QrizB

Dolor said:

There have been a number of studies which have concluded that most homes have boilers that rarely condense.

There's a window near my boiler and I can see the difference in the nature of the flue between condensing and non-condensing.

If the flow temperature is low enough, on a cold day the flue gases are visible but the steam is light and wispy; if I turn the temperature up the flue looks more like a hard-pressed steam loco.

Google image search isn't being very helpful. If we get a suitable day I'll try to take some photos.

BUFF

Dolor said:

I doubt that many homeowners have considered the need for bigger radiators or have made any attempts to re-balance their systems. There have been a number of studies which have concluded that most homes have boilers that rarely condense.

In an ideal world a heating installer would have talked through this with their customer beforehand.
Balancing the system should be part of a boiler install. I do agree that many condensing boilers in the past have been installed as replacements without their flow/return temps being set correctly.

(Mine is currently running at 53C flow but with the programmer set to allow for the increased time for internal temps to increase/recover. If ambient temps drop down to freezing I put flow temp up) 

markin

Most would not just give up after a short test, try a lower temp and get more data, what was the inside temp and was the outside temp and wind consistent?

You really should measure the return temp also so you know what you're working with.