Home page F.A.Q. E-MAIL TOC
A Gas central heating boiler (Heat Generator) is like the engine of a car, this provides the heat that the property needs to warm itself up.
The size of the boiler should be matched to the size of the property. If the boiler is oversized, then the fuel bills will be excessive. If the boiler is undersized, it may not generate enough heat in winter. The ideal size for a boiler is one that just copes adequately on the coldest day of the year. Most boilers are oversized by at least 30%. This is due to the way systems used to be calculated with a card calculator. These always over calculated “to be on the safe side”. Today the emphasis is on energy conservation, and the fact that heat loss calculations can be done very accurately on a PC, Means there is no need to oversize. This allows smaller radiators and so less water in the system, which it turn means a smaller boiler and reduced costs for both installation and fuel bills.
The boiler doesn't directly govern the amount of radiators fitted to the system. It is the power of the pump and circulation of the water through adequately sized pipes that determines the number of radiators you can have. But the total output of all the radiators, pipes and cylinders determines the size of the boiler.
Flueing & Ventilation All gas-burning appliances need air to burn and need to be able to get rid of the burnt gas, i.e. out via a flue. Most modern boilers are called room sealed (Balance Flue) which means all the air for combustion of the gas is taken from outside, through a duct and the fumes from the burnt gas are taken through a second duct, back outside (usually the flue duct is inside the air duct). Alternatively, it is possible to get boilers that are open flue. (Not Recommended) These take air for combustion through an air grill fitted in the room where the boiler is located. The fumes then go up the flue, which terminates above the roof. If for any reason the flue gets damaged or the ventilation grill gets blocked, or even a fault develops within the boiler itself, poisonous fumes could enter the living space. So open flue boilers should never be considered when fitting or replacing a central heating boiler, although new boilers do have extra safety devices.
All new boilers now are fanned flue and room sealed , which is the best and safest option. Some boilers use a fan in conjunction with an open flue. and as from 1st April 2005 al new boilers install must be over 90% efficient unless there are exceptional circumstances
Most boilers also need extra air to keep them cool, especially if fitted in a small compartment, however some modern boilers do not need any extra cooling air. The size and position of ventilation depends on the heat input of the boiler, the type of flue and where the air is coming from.
There are a lot of regulations for safety of the flue and ventilation, so if you are in any doubt consult a "Gas Safe Registered" registered installer to check this. All gas appliances should be checked for safety once a year, any faults or potential faults should be picked up then.