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Boiler Sizing Guide

Planning to install a new boiler? Check out our sizing guide for the right unit that will fit your needs! Call 020 8882 2266 for professional installations in the London area.

This guide will help you choose the correct sized boiler for your property. It is designed to be used by heating engineers and homeowners.

The purpose of this guide is for heating engineers and homeowners to be able to correctly size which boiler heat output is required.

You will need to set aside 30-60 minutes of your time to complete the measurements and calculations required.

City Gas Services reserve all rights to this guide. We will give no responsibility for any person following this guide and selecting an output based on the calculations in this guide.

How to use the worksheet:

Complete sections 1-7 by filling in the blank areas. Follow the instructions carefully.

If the property you are measuring is an irregular shape, you will need to divide into sections and complete separate worksheets for each section.

Important: Where the calculations ask for a table value/factor, use the table on page 4 and choose the relevant value/factors.

Replacement boilers are often sized incorrectly. The aim of this guide is to reduce the unnecessary emissions from oversized boilers and the loss of efficiency caused by boilers cycling.

Not only are oversized boilers more expensive to buy in the first instance, they are also more expensive to maintain and have higher running costs.



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At London Boilers we offer the highest standard in boiler installation, repairs and servicing. We are a plumbing specialist company and we offer our services in North London and Central London.

Have a look at the areas we cover or get in touch with us.

London Boilers
70 Aldermans Hill London, Greater London N13 4PP
Phone: 020 8882 2266
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