01-02-2012, 06:51 PM
A few points that might help Ed:
At best, your Glow Worm boiler will be 55-65% efficient, made worse by the fact that it has a permanent pilot, which is rather like having a 24/7 gas leak, except that the gas is alight in the boiler! It is so innefficient that it would have instantly qualified for the £400 government grant when it was in being.
Your boiler being a '65-80' means that it was 'range rated' which - by varying the gas burner pressure - could have the heat output varied from 65,000 BTUs to 80,000 BTUs. Nowadays, boiler heat outputs are quoted in KW/H. A KW/H is equal to 3,412 BTUs, so for example, a 25KW/H boiler will equate to 25 x 3,412 = 85,300 BTUs.
A condensing boiler will have a rated efficiency of 90%+, in Band A of the SEDBUK rating. You can check the effeciency ratings of a whole range of current production boilers at the SEDBUK site. (SEDBUK is th national standard for all domestic heating boilers in the UK, whatever the fuel source, and is an acronym for 'Seasonal Efficency Of Domestic Boilers in the UK'. (Current boilers are all very similar in efficiency).
You ask about fuel savings. The SEDBUK site has an annual fuel saving cost calculator where you can input your present gas consumption figures and see what savings you would make with a condensing boiler.
There's lots more information at the SEBUK site, which is here:
http://www.sedbuk.com/
It's almost impossible to make meaningful assessments of fuel savings from one year to the next - you can only compare an inefficent boiler with the consumption of a fuel-effecient boiler to genenrate the same amount of heat. The amount that your boiler actually consumes over a heating season from one year to the next is highly sensitive to outside temperatures, which is calculated historically on what's known as 'degree days'.
The temperature at which you set your room thermostat, and the number of hours per day your programmer is set to also has an enormous bearing on consumption. My house has double glazing, cavity wall insulation, and 300mm of roof insulation. Let's assume that with the heating off, my house has an indoor temerature of 10 C. If I set the room thermostat to 20C, that's a temperature rise of 10C. But 20C far to chilly for my old bones, so I have it set at 23C - nice and toasty! But that increases the consumption by 15%, so if saving money was a high priority, I'd put a pullover on and turn the room thermostat down, but comfort ranks higher than cost with me, so 23C it is!
As to how you go about replacing your boiler with a condensing one, assuming that you wish to comply with non-statutory and statutory guidance and requirements, there is a 'Guide to Condensing Boiler Assesment Procedure' which sets out the criteria for the siting of boilers, flues, and so on.
Though there are non-condensing boilers on the market, they're not simply a matter of personal choice, (whether down to financial or practial considerations). To comply with codes of practice - as any reputable installer would do - a non-condensing 'high efficiency' boiler (deemed to have an efficeincy of >72%) should only be installed where it impracticable to fit a condensing boiler, which is only going to be in exceptional circumstances. The Guide sets out the critieria in which a non-condensing boiler will satisfy the requirments of a Building Control Officer. (Not relevant in your case Ed as you've decided on a condensing boiler anyway).
You mention that you believe that the boiler will be a balanced flue one, and that's correct. All boilers nowadays must be balanced flue (except fire/back boilers, which are frowned upon except as replacements). From what you say, your present boiler is a conventional open flued boiler which takes its combustion air from within the room in which it is sited, and discharges the products of combustion up a flue (lined chimney?).
Older balanced flue boilers had to be sited on an outside wall as the flue box bolted onto the back of the boiler. A modern balanced flue condensing boiler flue is fan-assisted, and has two concentric flue pies - the outer one drawing in the combustion air - the inner one discharging the products of combustion ('fumes') which consist of water vapour and carbon dioxide. Condesing boilers have a lot of flexibilty in their flueing arrangments, in that you can have quite long horizontal and vertical runs, and 90 degree bends (a 90 degree bend being equivalent to 1.3M length of flue when calculating the flue length).
I haven't looked at individual makers' technical data, but to my mind, a vertical concentric fan assited flue length of 9M sounds a bit bizarre. All that your existing flue has to do is to work as a chimney, but a condensing boiler fan would have to draw the combustion air down 9 metres of concentric flue pipe, and shove the products of combustion back up another 9 Metres into the atmosphere. Are you quite sure that there's no other way of running a horizontal flue from the top of the boiler to an outside wall, provided that the flue terminal positions complies with the criteria set out is the assesment guide? (A 'horizontal' flue should actually have a slight slope towads the boiler for any condensate that forms in the flue to drain back into the boiler).
As to reliabilty, in the early days of condensing boilers (which have been around for 20 years or so), some got a bad reputation for heat exchanger failure, but modern ones have stainless steel heat exchangers, which in part, helps bump up the cost.
Most problems these days - particualrly last winter - have been down to poor installation of condensate drains, often with blatant disregard for makers' instructions, with long runs of exposed condensate drains prone to freezing. You've said that the condensate drain isn't an issue in your case Ed. An indication of reliaiblty can be assumed from Worcester Bosch who give a two-year warranty and Baxi, five years. Worcester Bosch have a good record of relibilty, and excellent service back-up and installer training facilities. Our Worcester Bosch 'Greenstar Ri' (25kW) has been in for two years now, and has never skipped a beat.
Finally, on the 'solar coil' you intend to fit in the cylinder, presumably there is some thermostatic arrangement whereby if the water temerature in the cylinder is higher than that from the solar panel, a thermostatic valve closes the circulation off from the panel, otherwise it would send lukewarm water down to the cylinder, and hot water out of the cylinder back to the panel to heat up the atmosphere - a sort of 'district heating scheme'!
Hope these lengthy notes are of use for reference Ed. (Safety Warning: May induce drowsiness - don't read whilst operating machinery!).
David
At best, your Glow Worm boiler will be 55-65% efficient, made worse by the fact that it has a permanent pilot, which is rather like having a 24/7 gas leak, except that the gas is alight in the boiler! It is so innefficient that it would have instantly qualified for the £400 government grant when it was in being.
Your boiler being a '65-80' means that it was 'range rated' which - by varying the gas burner pressure - could have the heat output varied from 65,000 BTUs to 80,000 BTUs. Nowadays, boiler heat outputs are quoted in KW/H. A KW/H is equal to 3,412 BTUs, so for example, a 25KW/H boiler will equate to 25 x 3,412 = 85,300 BTUs.
A condensing boiler will have a rated efficiency of 90%+, in Band A of the SEDBUK rating. You can check the effeciency ratings of a whole range of current production boilers at the SEDBUK site. (SEDBUK is th national standard for all domestic heating boilers in the UK, whatever the fuel source, and is an acronym for 'Seasonal Efficency Of Domestic Boilers in the UK'. (Current boilers are all very similar in efficiency).
You ask about fuel savings. The SEDBUK site has an annual fuel saving cost calculator where you can input your present gas consumption figures and see what savings you would make with a condensing boiler.
There's lots more information at the SEBUK site, which is here:
http://www.sedbuk.com/
It's almost impossible to make meaningful assessments of fuel savings from one year to the next - you can only compare an inefficent boiler with the consumption of a fuel-effecient boiler to genenrate the same amount of heat. The amount that your boiler actually consumes over a heating season from one year to the next is highly sensitive to outside temperatures, which is calculated historically on what's known as 'degree days'.
The temperature at which you set your room thermostat, and the number of hours per day your programmer is set to also has an enormous bearing on consumption. My house has double glazing, cavity wall insulation, and 300mm of roof insulation. Let's assume that with the heating off, my house has an indoor temerature of 10 C. If I set the room thermostat to 20C, that's a temperature rise of 10C. But 20C far to chilly for my old bones, so I have it set at 23C - nice and toasty! But that increases the consumption by 15%, so if saving money was a high priority, I'd put a pullover on and turn the room thermostat down, but comfort ranks higher than cost with me, so 23C it is!
As to how you go about replacing your boiler with a condensing one, assuming that you wish to comply with non-statutory and statutory guidance and requirements, there is a 'Guide to Condensing Boiler Assesment Procedure' which sets out the criteria for the siting of boilers, flues, and so on.
Though there are non-condensing boilers on the market, they're not simply a matter of personal choice, (whether down to financial or practial considerations). To comply with codes of practice - as any reputable installer would do - a non-condensing 'high efficiency' boiler (deemed to have an efficeincy of >72%) should only be installed where it impracticable to fit a condensing boiler, which is only going to be in exceptional circumstances. The Guide sets out the critieria in which a non-condensing boiler will satisfy the requirments of a Building Control Officer. (Not relevant in your case Ed as you've decided on a condensing boiler anyway).
You mention that you believe that the boiler will be a balanced flue one, and that's correct. All boilers nowadays must be balanced flue (except fire/back boilers, which are frowned upon except as replacements). From what you say, your present boiler is a conventional open flued boiler which takes its combustion air from within the room in which it is sited, and discharges the products of combustion up a flue (lined chimney?).
Older balanced flue boilers had to be sited on an outside wall as the flue box bolted onto the back of the boiler. A modern balanced flue condensing boiler flue is fan-assisted, and has two concentric flue pies - the outer one drawing in the combustion air - the inner one discharging the products of combustion ('fumes') which consist of water vapour and carbon dioxide. Condesing boilers have a lot of flexibilty in their flueing arrangments, in that you can have quite long horizontal and vertical runs, and 90 degree bends (a 90 degree bend being equivalent to 1.3M length of flue when calculating the flue length).
I haven't looked at individual makers' technical data, but to my mind, a vertical concentric fan assited flue length of 9M sounds a bit bizarre. All that your existing flue has to do is to work as a chimney, but a condensing boiler fan would have to draw the combustion air down 9 metres of concentric flue pipe, and shove the products of combustion back up another 9 Metres into the atmosphere. Are you quite sure that there's no other way of running a horizontal flue from the top of the boiler to an outside wall, provided that the flue terminal positions complies with the criteria set out is the assesment guide? (A 'horizontal' flue should actually have a slight slope towads the boiler for any condensate that forms in the flue to drain back into the boiler).
As to reliabilty, in the early days of condensing boilers (which have been around for 20 years or so), some got a bad reputation for heat exchanger failure, but modern ones have stainless steel heat exchangers, which in part, helps bump up the cost.
Most problems these days - particualrly last winter - have been down to poor installation of condensate drains, often with blatant disregard for makers' instructions, with long runs of exposed condensate drains prone to freezing. You've said that the condensate drain isn't an issue in your case Ed. An indication of reliaiblty can be assumed from Worcester Bosch who give a two-year warranty and Baxi, five years. Worcester Bosch have a good record of relibilty, and excellent service back-up and installer training facilities. Our Worcester Bosch 'Greenstar Ri' (25kW) has been in for two years now, and has never skipped a beat.
Finally, on the 'solar coil' you intend to fit in the cylinder, presumably there is some thermostatic arrangement whereby if the water temerature in the cylinder is higher than that from the solar panel, a thermostatic valve closes the circulation off from the panel, otherwise it would send lukewarm water down to the cylinder, and hot water out of the cylinder back to the panel to heat up the atmosphere - a sort of 'district heating scheme'!
Hope these lengthy notes are of use for reference Ed. (Safety Warning: May induce drowsiness - don't read whilst operating machinery!).
David
Regards, David.
BVWS Member.
G-QRP Club Member 1339.
'I'm in my own little world, but I'm happy, and they know me here'
BVWS Member.
G-QRP Club Member 1339.
'I'm in my own little world, but I'm happy, and they know me here'
