A Condensing Boiler Sizing Guide

A condensing boiler was designed to be more efficient than a conventional boiler. It achieves this by reducing the temperature of the flue gasses where latent heat is released rather than escaping with the flue gases. In order to accomplish this, a condensing boiler will use either an extra large heat exchanger or a second heat exchanger.  This will collect the heat from the flue gases. Basically, it uses what would be wasted and recycles that into heat. The end result is that less heat is lost than a conventional boiler and it runs more efficiently. The boiler can run on natural gas, LPG and on oil. Are best suited for large properties or where there is a higher load level. Sizing the condensation boiler to your home is quite important, a condensing boiler sizing guide can help you in the right direction as to which boiler to choose. It is very common that a replacement boiler will be sized correctly. An over-sized boiler is more expensive to purchase and will result in higher costs to operate because it is not running efficiently in a smaller space. It will also cause more unnecessary emissions into the atmosphere.

Whole House Boiler Sizing

Keep in mind that this is just a rough guide. If you are beginning your research into a new boiler, this will give you guidance. You should calculate as accurately as you can the size of the home (measuring outside footprint, the height of your rooms, the stories of your home, and the number of windows), as the whole house sizing method takes into consider the individual characteristics of your home. All of these factors listed will come into play when calculating the heat loss and the proper boiler size.

Analyzing 4 Home Sizes

Here is an analysis of four different home sizes and see the difference in the boiler size required. We will keep most of the variables constant and only change one dimension of the home. We will assume the following factors: the house has only one floor, it is a single family home with four walls that are not attached to any other building, the windows are of average number for the size and are double glazed, the roof it pitched and the climate is seasonally cool, with a change of seasons.

  1. The house has measurements (in meters) of 10 x 4 with a 4 meter high ceiling.
    The boiler required would need a 19.1kw output
  2. The house has measurements (in meters) of 15 x 4 with a 4 meter high ceiling. 
    The boiler required would need a 25.8kw output
  3. The house has measurements (in meters) of 20 x 4 with a 4 meter high ceiling. 
    The boiler required would need a 32.6kw output
  4. The house has measurements (in meters) of 25 x 4 with a 4 meter high ceiling. 
    The boiler required would need a 39.3kw output

Obviously, as expected, the larger the house, the higher output would be required. You can see that there is almost a pattern in the results as the home size increases.

Check with your installer for up-to-date information on the condensing boilers available and match them to your home’s conditions to achieve the best efficiency.