I'm a newbi to this forum and would like your advice. I'm planning a new Combi central heating system. I have worked out the heat requirement for the house (A 1890's 3 bedroom end terraced house). The heat requirement is 34,000BTU or 10 KW. I have been told that I do not have to add any extra BTUs for water heating in a Combi system. If this is correct the boiler appears rather small. Have I got something wrong?