There are very large domestic combi boilers in the marketplace. For example, Alpha make a 38kW combi, which is among the highest outputs at 15.9 litres per minute of DHW (Domestic Hot Water) on the market. However, we always recommend discussing your actual hot water requirements with an expert Gas Safe registered installer or a boiler manufacturer. This is because many people over-estimate their needs and risk ending up with a far more expensive boiler than they need.

However, as a general guide, boiler size relates to the kW output rating which tells you how much power a boiler can provide to your heating and hot water system. If you then work out your household demands based on the criteria below you will get a good idea of how much power you will need. You may also find that bigger boiler ie. a high power combi boiler is not always better or necessary.

  • Number of radiators
  • Number of bathrooms
  • Number of people
  • Gas and water supply sizes

This will give you a good starting point and help you to avoid getting a boiler that is too powerful which would lead to performance issues and wasted energy. Sometimes the most compact combi boiler can be just right for a larger home.

For households that genuinely have above-average hot water demands and require hot water for long periods or high flow rates even when demand is high, Alpha offer an excellent extra solution. Offering a ‘best-of-both worlds’ scenario, FlowSmart from Alpha delivers the energy-saving qualities of a combi and the same performance you would get if you were to buy a conventional boiler. Using approximately 25% less gas than a system boiler and more than matching the hot water performance, FlowSmart enables large households to enjoy the energy efficiency benefits of the combination boiler.