What Size Boiler For My House?

Choosing the right size combi boiler for your home can be bewildering, and whilst it is advisable to consult a Heating Engineer or Gas Safe Plumber to give you advice on your selection it is useful to have an idea of what you will need for budgeting. We have given a rough guide below to help you plan.

What size boiler for my house?

Combi boilers are available in three size ranges here at Mr Central Heating; 24 to 27kw, 28 to 34kw and 35 to 42kw.

  • As a rough estimate most flats, apartments and smaller houses, with up to 10, average size radiators and 1 bathroom* will require a 24 to 27kw Combi Boiler.
  • For a medium to large 3-4 bed house with up to 15 average size radiators, 1 bathroom and an ensuite* a 28-34kw Combi Boiler would be installed.
  • A 35kw and a 42kw Combi boiler would be for a large house with anything up to 20 average size radiators and 2 bathrooms*.

For properties where a higher demand of hot water is needed the higher the kw of the boiler, the better the flow rate of hot water will be.

*However combi boilers do not cope well with 2 showers running at the same time in the same property. Where this is a requirement a system boiler with an unvented cylinder should be considered.

What is a Combi boiler?

A combi boiler (or to give it it's full name a combination boiler) is the name given to a boiler that provides heat for central heating and heats water instantaneously on the opening of a hot tap.

With a combi there are no tanks in the loft and no storage cylinder. The water is fed from the mains so the water pressure is generally greater. The diagram below is an illustration of how a combination boiler looks within a house.

combi boiler layout


This information is not going to be accurate for every property as room sizes can vary wildly from property to property, but will give you a good idea when consulting with a heating engineer over your needs.

8 thoughts on “What Size Boiler For My House?”

  • I am about to start building a Pssive Spec house and need advise as to what size boiler I need.
    Tel 07970 911778

  • Currently my water gets cold real fast when i am taking a shower. What is a good size boiler for a 1 and 1/2 bedroom medium house

  • Hi, I need advice on what boiler wattage I require for a ground floor 4 bedroom flat? It is a council block and it has 3 floors above me. 1 bathroom with electric shower

  • What power gas boiler would I need for a 4bedroom house

  • for 3 bedroom House and 2 bathroom ,1 first fl and 1 to loft,1 kitchin with 10 radiators what size boiler I need!thank you!Daniel,

  • I have 3 bathroom with 3 showers. What bolier is best? Dont have space for a system bolier with tank?

  • We are about to build a 5 bedroomed, 4 bathroom and cloakroom house, approximately 4,333 sq ft
    What type of boiler would be recommended, the ground floor will have gas supplied underfloor heating. 1st and 2nd floor radiators.

    • Hello Angela,

      As your house it quite large, you would be better asking a plumber to come around and asses. You can use our installer database to help find a local plumber


      Thanks Mr Central Heating

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