Flow temp vs power rating

[John Smith Esq.]

Hi all,

I have my greenstar 25i combi set to 9.1KW and 53C flow temp. With the outside temperatures falling I want to know what would have the biggest effect on warmth indoors:

- increasing the rating to say 10.5kw
- increasing the flow temperature by 1 or 2 degrees
- increasing the amount of time the heating is on

However, I want to change the one that will increase warmth in the most efficient and economical way. I assume the last option will be effective but most costly. Which would win out of the first two?

There isn't much I can do to improve other factors like insulation.

Thanks

 

[Johntheo5]

Hi all,

I have my greenstar 25i combi set to 9.1KW and 53C flow temp. With the outside temperatures falling I want to know what would have the biggest effect on warmth indoors:

- increasing the rating to say 10.5kw
- increasing the flow temperature by 1 or 2 degrees
- increasing the amount of time the heating is on

However, I want to change the one that will increase warmth in the most efficient and economical way. I assume the last option will be effective but most costly. Which would win out of the first two?

There isn't much I can do to improve other factors like insulation.

Thanks

Increasing the rating will have no effect except that its present rating is stopping boiler flow temperature from reaching its set point so forget about that as a economy measure, it should be set to the max rating of your radiators, maybe something like 15kw or so, the boiler will use the exact amount of fuel necessary to satisfy the flow temperature SP set by you, no more and no less.

Adjusting the flow temperature is the most convenient and easiest way of getting the optimum performance.

For every 1 DegC rise or fall in the OAT (outside air temperature) then the Boiler flow temperature should be decreased or increased by around 2 DegC which will result in ~ 4% increase/decrease in the power required or if you want to increase the room temperature (with no change in OAT) then use the same method, if, say you wish to increase the room temperature by 2 DegC then increase the boiler flow temp by 4C which will result in ~ a 8% increase in power demand.
Slight correction, for every 1 DegC increase/decrease in required room temp, increase/decrease the boiler flowtemp by 3 DegC, the extra power will still be the same + or - 4%.

 

[John Smith Esq.]

Increasing the rating will have no effect except that its present rating is stopping boiler flow temperature from reaching its set point so forget about that as a economy measure, it should be set to the max rating of your radiators, maybe something like 15kw or so, the boiler will use the exact amount of fuel necessary to satisfy the flow temperature SP set by you, no more and no less.

Adjusting the flow temperature is the most convenient and easiest way of getting the optimum performance.

For every 1 DegC rise or fall in the OAT (outside air temperature) then the Boiler flow temperature should be decreased or increased by around 2 DegC which will result in ~ 4% increase/decrease in the power required or if you want to increase the room temperature (with no change in OAT) then use the same method, if, say you wish to increase the room temperature by 2 DegC then increase the boiler flow temp by 4C which will result in ~ a 8% increase in power demand.
Slight correction, for every 1 DegC increase/decrease in required room temp, increase/decrease the boiler flowtemp by 3 DegC, the extra power will still be the same + or - 4%.

Thanks for this, very helpful and interesting.

Just to say, the boiler does reach the set flow temperature with the rating set to 9.1KW. Perhaps slower than might otherwise be the case. Presumably it saves electricity if not gas to have the rating lower?

I have increased the rating to 12KW. I have 9 radiators in this three bed bungalow, 7 of those are doubles, the other two are a single and a towel one in bathroom. Some of the pipes on the attic do have to travel a way through to reach two of the further away radiators. I gather 12KW is a bit more aligned with the situation, and still only half what the boiler is capable of.

I've also increased the flow temp to 54 for now. I'm finding the house does get up to 20C within the three 2hr blocks I have it running for each day but will have to stop being so tight if needs required more heat. Also, I followed your advice and increased the anti fast temperature to -14. It does seem to result in less stop-start operation by the boiler - plus I assume the average flow temp is less overall since it isn't constantly overshooting the set flow temp. So less gas used and more condensing.

On a separate note, after I cleaned out the magnetic filter the other day and lost about 4L of water (which I obviously replaced) would you now add more inhibitor? The trouble is, I don't know what inhibitor was put in last year when two radiators were replaced. Some people say brands don't matter, others say they shouldn't be mixed. I was going to get Fernox Express and add it through the filter. If it is necessary to drain the system, would I get away with just doing half to at least reduce the existing chemicals by that amount, or do I have to drain the lot? I'd be doing this through the filter using a bucket. I realise several trips to the drain would be necessary.