Boiler Size for 18 Radiators & 210L Unvented Cylinder

If you take you need 1.5 kw for some big radiators and atleast 1 kw per radiator then even without the tank the boiler would be struggling to cope

Most rads will use roughly a kilowatt of energy. If you have 18 rads and an 18kw boiler it sounds like the boiler is undersized. Obviously could be other issues but mathematically it doesn’t really add up.

undersized boiler for your heating system , you will probably need to increase your expansion capacity for a system of that size.

Hello there, It is not necessary to have the radiators piping hot in order to heat a house, because even if they are not piping hot but giving a bit of extra time the property would become hot. If the radiators were piping hot that would be a signal of that your radiators do not have enough time to transmit into the property the amount of heat that the boiler is providing, which would mean that possibly your boiler would be working not very efficiently, therefore wasting gas. The important matter would not be the number of radiators you have, but what type of property you have and how well insulated it is, type of loft, type of windows, drafting etc, how cold is the area where the property is etc. There are 18 radiators but that doesn’t mean that the heat losses of the property are 18 x 1kw or 2kw ?. Perhaps you have extended the house and also making it better insulated throughout the house ?. Generally speaking an 18kW boiler if it is programmed to work in that uneficient way it would be able to heat 18 radiators of average property and keep all them piping hot. However, you would save gas if the central heating is working for longer period of time throughout the day and the radiators do not become piping hot. There are many free websites that would help you to calculate the heat losses of your property, like this one below, then with the result you would have a good indication if your boiler is too small for the property. http://www.geyser.co.uk/heat-requirement-calculator-i-36.html#