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Central Heating

Boiler replacement

Which Worcester combi boiler would be best for 4 bed semi with ten rads? The Greenstar 42CDi or 25si

1 Answer from a MyBuilder Heating Engineer

Best Answer

Hi Terez,
When selecting a boiler, you could benefit the choice by applying a little bit of calculation. Boilers are sized by the kw heat output. The two boilers output are broadly referenced as 25 & 42 kw respectively. These outputs are nominal. Take a modern double panel 1200mm radiator, this could have an output of 2kw. Based purely on these two facts, one could assume that 10 radiators @ 2kw each, could be fully delivered by a 20kw output boiler. Personally I over-rate boilers to allow for the boiler reduction in efficient over its life cycle (SEDBUK avg 90%). This being said, if you moved your central heating system and radiators into an extremely large house, 20kw heating would probably not offer sufficient heat overall. One man's four-bed house is another man's castle. Please factor in your hotwater usage, the flow rate of the CDI is greater than the SI and this is impacted further by Bath / Shower requirements. Sorry that I can't suggest Boiler A over Boiler B, but the selection invariably will require you to determine heating demand, which can't be determined on just property type and radiator quantity. Best of luck.

2015-06-12T09:30:02+01:00

Answered 12th Jun 2015

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