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Oct 4, 2017
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Spilsby
Member Type
DIY or Homeowner
Hi I’m looking to buy a new Combi oil boiler but don’t know what size to go for my old boiler was a Worcester heatslave 12/14 which was running originally 12 rads and one bathroom when I moved in. I then added a rad I believe it was to small to begin with as it was always breaking down it now has packed in completely in addition I’m currently having an extension built which new lounge with the two of the largest rads I can find and two small doubles in the utility and shower the downstairs shower room the shower will be electric so the only hot water demand would be the kitchen sink utility sink and the very occasional bath I would be looking at an external boiler to save space
 
You need to calculate the property heat loss properly, guides can be found online. Too small a boiler wont generate enough power to satisfy the load/loads and too big presents it's own problems as well, ie, uses more fuel and too high return temperatures resulting in not condensing etc. If you're having a extension built then your builder or plumber will be able to help
 

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