Boiler size confusion
Discussion
Hi everybody,
I asked this question on diynot and didn't get a definitive answer and seemed to wind people up by not being descriptive enough. I will try a little harder here. I have just moved into a new house which has two combi boilers, one per floor (it's a large house). I have added up the heating capacity and it is 30 kW although since we have only just moved in, we don't know whether it will be cold in the winter. The house was built in 2002 so the insulation standards are pretty good although it has an above average amount of glass.
I would like to replace the combis (which are leaking and reaching the end of their lives in my opinion) with a 300 litre unvented tank and system boiler. There are four bathrooms and I am hoping that the tank will mean that multiple bathrooms can be used at any one time and the boiler fitters that have visited so far are not worried about the flow or pressure. My worry is the size of the system boiler. The first person recommended 80 kW (and then reduced this to 60 kW) with a twin coil unvented tank but he generally fits commercial boilers and argued that I will want a big boiler to provide heating and low reheat times on the tank. The next two that have visited have recommended the Vaillant ecotec 37 kW boiler stating that this more than covers the heating demand whilst providing sufficient heat for the hot water tank, which will be reheated in preference to the heating anyway. I agree with this argument but I don't know if there is something I am missing.
This is clearly a big difference! I am not sure which is right. It might be that the second and third installers know 37 kW is on the small side but don't want to fit a non-domestic boiler, or that the first installer only knows commercial systems and is over-specifying the boiler.
Can anybody give their view on what might be right please? We would like to design to the maximum occupancy of the house rather than what we need today (two combis would be fine for today!) but I don't want to massively overspend for no reason. I have also seen that Intergas do a 40 kW system boiler which feels better sized but I know very little about this brand.
Thanks for your advice in advance.
I asked this question on diynot and didn't get a definitive answer and seemed to wind people up by not being descriptive enough. I will try a little harder here. I have just moved into a new house which has two combi boilers, one per floor (it's a large house). I have added up the heating capacity and it is 30 kW although since we have only just moved in, we don't know whether it will be cold in the winter. The house was built in 2002 so the insulation standards are pretty good although it has an above average amount of glass.
I would like to replace the combis (which are leaking and reaching the end of their lives in my opinion) with a 300 litre unvented tank and system boiler. There are four bathrooms and I am hoping that the tank will mean that multiple bathrooms can be used at any one time and the boiler fitters that have visited so far are not worried about the flow or pressure. My worry is the size of the system boiler. The first person recommended 80 kW (and then reduced this to 60 kW) with a twin coil unvented tank but he generally fits commercial boilers and argued that I will want a big boiler to provide heating and low reheat times on the tank. The next two that have visited have recommended the Vaillant ecotec 37 kW boiler stating that this more than covers the heating demand whilst providing sufficient heat for the hot water tank, which will be reheated in preference to the heating anyway. I agree with this argument but I don't know if there is something I am missing.
This is clearly a big difference! I am not sure which is right. It might be that the second and third installers know 37 kW is on the small side but don't want to fit a non-domestic boiler, or that the first installer only knows commercial systems and is over-specifying the boiler.
Can anybody give their view on what might be right please? We would like to design to the maximum occupancy of the house rather than what we need today (two combis would be fine for today!) but I don't want to massively overspend for no reason. I have also seen that Intergas do a 40 kW system boiler which feels better sized but I know very little about this brand.
Thanks for your advice in advance.
http://www.ukplumbersforums.co.uk/forums/central-h...
some knowledgeable installers will help you in here
some knowledgeable installers will help you in here
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