If you have a heating system currently doing the job, the easiest boiler sizing indication is the nameplate which will state it’s BTU or kW rating. If you don’t have this, a quick rule of thumb to start you on the way is to calculate the following: Total Square Footage you want to heat ÷ 100 = Kw rating of your boiler. For eg. 10,000 square feet ÷ 100 = 100kW rating for your boiler.
Of course there are many more factors to consider before you make a final decision. To learn more, read our Sizing Guide.