Boiler Guides

What size boiler do you need?

Making sure you have the right size boiler is essential when you’re buying a new model. If it's too small it might not meet your needs; too big and it will be over-costly, inefficient, more expensive to run, and be even more damaging to the environment.

There are a number of different factors that affect the size of the boiler that you’ll need to consider and it can be a complicated process. So if you don’t want the hassle of working it all out for yourself, get a boiler quote and let an Association of Gas Safety Managers (AGSM - formally known as Corgi) registered engineer do all the hard work for you.

• House type
• House size
• External wall area
• Window heat loss
• Floors and roofs
• Water usage
• Get a boiler quote

House type

If they’re not properly insulated, detached, semi-detached and end-of-terrace houses lose more heat that many other homes as they have more external wall space and don’t benefit from the heat of surrounding properties.

House size

The size of your home, and the number of rooms, will affect the size and the type of boiler that you’ll need. Larger houses - and those with bigger rooms and higher ceilings - obviously cost more to heat and need larger boilers. However, by calculating each room size properly, you’ll be able to eliminate the risk of getting a boiler that’s too large.

External wall area

Heat is lost through the external walls of your home, so the more external wall space you have, the more will be lost - as much as 33% of your home’s heat if you have cavity walls.

It will help to have cavity wall insulation though, and you can save yourself at least £90 a year by having this done. Make sure you check out our guide to energy efficiency for other energy saving measures.

Window heat loss

As with your external walls, heat is also lost via your windows, and any that aren’t double glazed will cost you between £80 and £100 a year through wasted energy, according to the Energy Saving Trust.

Floors and roofs

Again, without proper insulation, floors and roofs - especially roofs - will lose heat, and this lost energy will affect the size of the boiler you need. Calculate the size of your floors and roof area, and make sure that you factor in any insulation.

Water usage

One of the major issues that will affect your boiler size is the amount of hot water you use. If you have a big family that likes to take long baths while another person has a shower and one does the washing up, then you need a boiler that will be able to cope with all that.

However, if you live by yourself and take quick showers, you’ll be able to get a far smaller, cheaper model.

Get a boiler quote

There is a lot to be considered when buying a new boiler, so why not simply get a registered AGSM engineer to give you a boiler quote - they’ll do all the hard work and you can rest assured that you’ll have the right size boiler to meet all your household needs.