Boiler Replacement - Selecting a Boiler
Our first “Gas Boiler Replacement” article dealt with why you might consider changing your boiler. Here we cover some points you might consider if you have decided that "yes, it's time for a new boiler"

We recommend that the most important thing to do is consult a Gas Safe registered heating engineer. The following information will give you a bit of background information for your discussion.

Condensing Boilers
  • Virtually all boilers on the market these days are condensing boilers.
  • In a condensing boiler heat that would normally be lost through the flue is actually used to heat the water passing through the boiler.
  • This increases the efficiency of condensing boilers compared to non condensing boilers.
  • Boilers with an energy efficiency rating of A convert around 90% of the fuel (Gas) to useable heat, whereas with older boilers this could be only 70%.
Combination Boilers 
  • There are two types of condensing boiler.
  • A combination boiler gives you instant hot water without the need for hot water to be stored in a cylinder.
  • A regular condensing boiler requires a cylinder to retain heated water ready for use when needed
  • Not all homes are compatible with combination boilers for example combi boilers cannot cope with two showers running at the same time.
  • A qualified heating engineer will inform you which type of boiler, regular or combination, is most suitable for your home.
Size / Power rating

When it comes to installing a boiler you want to make sure that the Power Rating (or size) of the boiler is just right. An undersized or oversized boiler will not run efficiently and so will consume more fuel and if it is working under strain it will be more likely to break down.

A heating engineer will carry out calculations that take into account potential heat loss in the property, the number of rooms (Bedrooms, bathrooms), number of people in the property, number of radiators and so on. 

However, as a rough guide most flats and smaller houses, with up to 10 radiators will require a 24-25kw boiler. A 28-30kw would be installed for a medium to large 3-4 bed house with up to 15 radiators, and a 33-35kw and a 40kw would be for a large house with anything up to 20 radiators. 

Boiler Manufacture

There are numerous boiler manufacturers each with different boiler models.

In our experience heating engineers will often favour the boiler of one particular manufacturer. 

The reason for this may be because they have had more specific training on that make or in their experience their preferred brand is less likely to go wrong. It could be that one brand is easier to install than another or that engineer is just more familiar with a particular brand than another. A Gas Safe engineer will be able to install a gas boiler of any brand but it’s worth listening to why they recommend one brand over another. You may find that they have a deal with the manufacturer to give an extended warranty on boilers they install.

Of course the budget you have comes into it. The same size boiler from one manufacturer may cost almost double that of another manufacturer. Although there are, of course, exceptions it’s fair to say that, in general, higher priced boilers are more reliable. So, although a lower price boiler may save you money in the short term you may spend more on maintenance, repairs and fuel in the future, as well as having to replace the boiler sooner.
More information?
This is the second of three articles designed, to some degree, to demystify the subject of replacing or installing a gas boiler. 

The articles are broken into three topics

To arrange for a thoroughly vetted, continually appraised Gas Safe engineer to provide you with a no obligation quote for a new boiler call 0131 315 0000, complete our Request-A-Visit form or email us on