Gas Boiler Efficiency
- Thread starter Hysteresis
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Search back over our posts and tell us when we don't help diyers on here 
You really need to lighten up and get a sense of humour. Usually in between the banter you will get an answer, but with your attitude I doubt it, even from Tony
You really need to lighten up and get a sense of humour. Usually in between the banter you will get an answer, but with your attitude I doubt it, even from Tony
N
namsag
Sir Sir those big boys have took my ball and won`t give it back to me. Stop being a big Jessie and take the rough with the smooth... And the Doctor answered your question within an hour of you asking so stop wingeing.
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D
Doctor Drivel
Agile said:
He quoted a ratio on CH and DHW consumption. That ratio will be roughly the same come inefficient or v efficient boiler. Other factors apply, like engineering the system to be more efficient. An inefficient system cannot be magically made super efficient by putting in new boiler - unless it is a one-box solution boiler such as an ACV HeatMaster or Atmos Multi, etc.
Hys, I am sorry that you have unfortunately and rather unfairly slightly upset some of the guys here but I will try to help you ( rather more than the Drivel above ).
Your boiler is a very unfortunate choice because it does not modulate and is almost certainly significantly oversized for your property. A typical 3-bed semi needs about 10kW-12kW. Much less than the 24 kW or so your boiler will give if its set to the full rated power. I dont think your boiler is meant to be range rated to a lower output !
Its basic efficiency is about 80% but when heating just water the cylinder is only able to absorb a small fraction of the heat from the boiler and this reduces as the cylinder warms up. This causes the boiler to cycle on/off and that greatly reduces the efficiency of the boiler to perhaps 50% or less.
However, gas is about 25% of the cost of electricity so the comparisom is more difficult and the amount of hot water usage affects the assessment as well.
I expect that if you turn the boiler stat down to about 70 C then it would be cheaper to use the gas when heating the cylinder up from cold. But reheating when only a small amount of HW has been used is likely to be more efficient with the immersion. Its the cycling which causes the worst case for you. While the boiler is full on its quite efficient.
These questions are not really very important. The main problem with your situation is your boiler is oversized and not modulating.
If you had a modern boiler like a Worcester 15Ri, which would probably be adequate for CH anyway, then it will modulate down to a level where it will stay on all the time and just give the heat output absorbed by the cylinder all at an efficiency of about 93% !!!
Does that help?
Tony
Your boiler is a very unfortunate choice because it does not modulate and is almost certainly significantly oversized for your property. A typical 3-bed semi needs about 10kW-12kW. Much less than the 24 kW or so your boiler will give if its set to the full rated power. I dont think your boiler is meant to be range rated to a lower output !
Its basic efficiency is about 80% but when heating just water the cylinder is only able to absorb a small fraction of the heat from the boiler and this reduces as the cylinder warms up. This causes the boiler to cycle on/off and that greatly reduces the efficiency of the boiler to perhaps 50% or less.
However, gas is about 25% of the cost of electricity so the comparisom is more difficult and the amount of hot water usage affects the assessment as well.
I expect that if you turn the boiler stat down to about 70 C then it would be cheaper to use the gas when heating the cylinder up from cold. But reheating when only a small amount of HW has been used is likely to be more efficient with the immersion. Its the cycling which causes the worst case for you. While the boiler is full on its quite efficient.
These questions are not really very important. The main problem with your situation is your boiler is oversized and not modulating.
If you had a modern boiler like a Worcester 15Ri, which would probably be adequate for CH anyway, then it will modulate down to a level where it will stay on all the time and just give the heat output absorbed by the cylinder all at an efficiency of about 93% !!!
Does that help?
Tony
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Hi Tony,
Thanks so much for your time, help and advice.
My own ignorance of domestic CH systems is aptly demonstrated here in that I was unaware of the existence of a Modulating Boiler for domestic systems. My experience with Boiler systems is large Industrial Boiler installations where rather complex and expensive dedicated control systems are used in which very accurate measurements of Fuel and Air are measured and used in PID Feedback computer control systems and of course the application is very much geared to very large Boiler systems. The domestic On/Off control of domestic systems is very inefficient and as such it is surprising a modulating boiler was not fitted to my house when it was built only 7 years ago, as clearly they were available at that time. Armed with your invaluable advice, my next house will undoubtably have the boiler you have suggested.
The On/Off control is inefficient but I think a boiler replacement is at this stage out of the question, due to the capital outlay.
The over sizing of my Boiler is the fault of the Building contractor who designed and built the house. I think my situation is made somewhat worse in that it is a 4 bedroomed detached house and there is only myself and my wife living here (The kids have long since flown the nest). The net result is that even in the Winter months three bedrooms are only marginally heated under the control of Thermostatic Valves. So as you suggest the boiler is oversized anyway and made even worse by the system not being fully loaded even in the depths of winter.
I think using your advice I would be maybe marginally better off using Electric, as our HW usage is not as great as a four person family would use.
The difference would be marginal I think. Would you agree?
The advice on Modulating Boilers is greatly appreciated and I am sure there will be quite a few Householder Numpties such as myself reading your advice that will benefit also.
The immature responses my genuine query generated are a reflection of some of the contributors who seem to take the view that it is a site for the type of discussion one would have in the pub were taking the mickey is the object of the conversation. My faith in the site has been restored by your reply. I was just about ready to stop using the site which would have been a bad move for me as Advice such as that which you have given is invaluable to the people such as myself who genuinely look to the professional who know their subject in great depth.
Thanks again for your time and invaluable advice.
Thanks so much for your time, help and advice.
My own ignorance of domestic CH systems is aptly demonstrated here in that I was unaware of the existence of a Modulating Boiler for domestic systems. My experience with Boiler systems is large Industrial Boiler installations where rather complex and expensive dedicated control systems are used in which very accurate measurements of Fuel and Air are measured and used in PID Feedback computer control systems and of course the application is very much geared to very large Boiler systems. The domestic On/Off control of domestic systems is very inefficient and as such it is surprising a modulating boiler was not fitted to my house when it was built only 7 years ago, as clearly they were available at that time. Armed with your invaluable advice, my next house will undoubtably have the boiler you have suggested.
The On/Off control is inefficient but I think a boiler replacement is at this stage out of the question, due to the capital outlay.
The over sizing of my Boiler is the fault of the Building contractor who designed and built the house. I think my situation is made somewhat worse in that it is a 4 bedroomed detached house and there is only myself and my wife living here (The kids have long since flown the nest). The net result is that even in the Winter months three bedrooms are only marginally heated under the control of Thermostatic Valves. So as you suggest the boiler is oversized anyway and made even worse by the system not being fully loaded even in the depths of winter.
I think using your advice I would be maybe marginally better off using Electric, as our HW usage is not as great as a four person family would use.
The difference would be marginal I think. Would you agree?
The advice on Modulating Boilers is greatly appreciated and I am sure there will be quite a few Householder Numpties such as myself reading your advice that will benefit also.
The immature responses my genuine query generated are a reflection of some of the contributors who seem to take the view that it is a site for the type of discussion one would have in the pub were taking the mickey is the object of the conversation. My faith in the site has been restored by your reply. I was just about ready to stop using the site which would have been a bad move for me as Advice such as that which you have given is invaluable to the people such as myself who genuinely look to the professional who know their subject in great depth.
Thanks again for your time and invaluable advice.
What ever. If we on here didn't feel dedicated to our work, we wouldn't bother to sit on here to help the miserable likes of you.
Christ sakes, we could all be dead tomorrow
It would be a really fun evening out with you and Tony I bet
Christ sakes, we could all be dead tomorrow
It would be a really fun evening out with you and Tony I bet
If as you say hysteresis you are geared up for commercial boilers
Then I cannot for the life of me not understand why you haven't fitted weather compensation etc.
There's a million little gadgets attached to commercial boilers that you can adapt to a domestic installation at very little DIY cost.
Then I cannot for the life of me not understand why you haven't fitted weather compensation etc.
There's a million little gadgets attached to commercial boilers that you can adapt to a domestic installation at very little DIY cost.
D
Doctor Drivel
Agile said:
No, that doesn't help much at all.
I cut from my post:
Other factors apply, like engineering the system to be more efficient. An inefficient system cannot be magically made super efficient by putting in new boiler - unless it is a one-box solution boiler such as an ACV HeatMaster or Atmos Multi, etc.
He could fit one of the above one box solutions or fit a heat bank, which will accept a non-modulating boiler no problem - and it will not cycle.
http://www.heatweb.com for heat bank explanation.
Fitting a modulating boiler to a cylinder with a small coil is futile. He would need a cylinder and a new boiler. Best he goes on-box solution or heat bank cylinder and keep the existing boiler.
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Do It All
I said Industrial not Commercial - Industrial as in very large steam generating plant for the Oil Industry.
I said Industrial not Commercial - Industrial as in very large steam generating plant for the Oil Industry.
if my caculations are right you have the ultimate 100
this is a non condensing band D boiler which is only 79.5% efficient. (test house figure) yours will probably be about 10% worse (69.5) due to poor system etc.
it makes no difference what you are heating as it is a heat only boiler and as such relies on a valve to direct water away from it to either rads, cylinder or both the boiler output is the same at all times. the only difference is amount of time it will fire for this depends on temperature of water in boiler / system pipework, temperature of water in cylinder, target temperatures of cylinder thermostat, room thermostat or both
the electric option is most expensive option to heat water without a doubt
this is a non condensing band D boiler which is only 79.5% efficient. (test house figure) yours will probably be about 10% worse (69.5) due to poor system etc.
it makes no difference what you are heating as it is a heat only boiler and as such relies on a valve to direct water away from it to either rads, cylinder or both the boiler output is the same at all times. the only difference is amount of time it will fire for this depends on temperature of water in boiler / system pipework, temperature of water in cylinder, target temperatures of cylinder thermostat, room thermostat or both
the electric option is most expensive option to heat water without a doubt
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Hi Kevindgas,
You are right the boiler is an Ultimate 100-FF and is installed on a fully pumped system using diverter valves for CW and HW. The product label is very difficult to read due to its location but using a mirror I can see that the heat input is rated at 29.87KW and the output 23.45KW giving a rated efficiency of 78.5%. I assume this rating is measured at full water flow rate through the boiler.
Having read with great interest yours and Agile's reply, my thoughts are to be dismissed as even with an inefficient use of the gas boiler, it will be still better than using electric immersion heaters.
I thank you both very much for you time and advice which I am sure will be of interest to other users of this fantastic site made all the more useful to us Numpties having access to you professionals. Thanks again
You are right the boiler is an Ultimate 100-FF and is installed on a fully pumped system using diverter valves for CW and HW. The product label is very difficult to read due to its location but using a mirror I can see that the heat input is rated at 29.87KW and the output 23.45KW giving a rated efficiency of 78.5%. I assume this rating is measured at full water flow rate through the boiler.
Having read with great interest yours and Agile's reply, my thoughts are to be dismissed as even with an inefficient use of the gas boiler, it will be still better than using electric immersion heaters.
I thank you both very much for you time and advice which I am sure will be of interest to other users of this fantastic site made all the more useful to us Numpties having access to you professionals. Thanks again
your welcome
i will let you into the secret i got the information from the little blue book of boilers! a really useful book. 20plus years in the trade also helps!
i will let you into the secret i got the information from the little blue book of boilers! a really useful book. 20plus years in the trade also helps!
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