Oil boiler size for large house

[john Reid]

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

 

[SimonG]

Do a full house heat loss calculation.

 

[john Reid]

Do a full house heat loss calculation.

How would I go about doing that?

 

[SJB060685]

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

 

[SimonG]

How would I go about doing that?

It's part of what you would be paying your installer for. But there are sites on the web to help if you fancy a crack yourself. Just have a google for heat loss calculations.