Boiler Size Help and information on all topics relating to your central heating, air conditioning and ventilation issues.

[PaulC 13]

Hi All

I'm a newbi to this forum, and need some advice. I'm planning to fit a combi central heating system, but have become a bit confused. I have calculated the heat requirement for each room and have come up with a figure of 34000 BTU which converts to just over 10 KW hr. I have been told that as it is a combi system I don't have to anything for hot water, but a 10 KW boiler is not very big. What am I doing wrong?

Thanks
Paul

[plumbbob]

Calculating boiler size for combi boilers is different to conventional calculations. In fact it is opposite.

Instant water heating requires a massive capacity boiler usually far in excess of any heating requirement. To calculate boiler size nowadays, consider your hot water requirements. How many showers does your house have? What are the flow rates? The size must be sufficient to satisfy this need.

Efficiency is maintained when only the heating is being called for by the modern boilers ability to be "fully modulating" ie, boiler output is automatically altered according to demand.