What output requirements do I need from my new
boiler?
Most boiler manufacturers provide technical information about
their new boilers but this can be quite difficult to understand. Here are some of the more common abbreviations and their
meanings.
DHW 12.1
Domestic Hot Water output at 35oC is 12.1 litres a minute. Although most manufacturers use the industry standard measurement of 35 celcius some also advertise at
30 celcius giving a distorted view to the consumer.
The output of a boiler may vary between as low as 8 litres
to over 15 litres per minute and is generally reflected in the price. A typical 3 bedroom semi-detatched house with an
average demand for hot water may need a boiler with around 11 litres of dhw a minute.
CH output Central
heating output tends to be measured since decimalisation in kilowatts however lots of people still use BTU's (British
Thermal Units). 1 kilowatt = 3413 btu's
Combination boilers require more kilowatts than traditional heat
only or system boilers which have a separate cylinder for the dhw. A typical combination boiler (a boiler that meets the
needs of the central heating and the hotwater, without the need for a separate cylinder) required for a standard
3 bedroom semi-detached house may be as little as 24 kilowatts if the right environmental controls are used e.g
Thermostatic radiator valves. The amount can be halved to 12 kwh for a conventional boiler.
One way of estimating your CH heating output requirement
is to add together the btu's of your combined radiators along with a small amount of btu's for heat loss through
your pipes. This will give you a general rule of thumb
requirement for your house.
External factors can effect requirement through
heat loss e.g lack of insulation, double glazing, brick type etc.
