For the past 20 years my home has been heated more than adequately with a 15kw boiler. I approached Glow Green for a quote. I told them this. Twice on the phone and once by email. They insisted I needed a 24kw boiler. I have some knowledge of heating systems having worked in this area for over 20 years. An oversized boiler leads to excessive gas usage, cycling, and unnecessary green house gas emissions. The salesman (with all of his 2 years "experience") even tried to tell me I was wrong and that my old boiler hadn't been heating my house. Avoid this company, they don't know what they are doing and are using the "bigger is better" excuse.