Boiler size is determined by kilowatt (kW) output. A higher kW rating means the boiler can meet greater demands for heating and hot water. Here’s a quick guide to combi boiler sizing:

• 2-Bedroom House: 26 kW for one bath, 29 kW for two.
• 3-Bedroom House: 29 kW for one bath, 35 kW for two.
• 4-5 Bedroom House: 35 kW for homes with multiple bathrooms.