Boiler type and Positioning

What type of boiler is the most suitable and where should it be fitted

Having Calculated the boiler size, there remains the questions of What type of boiler should be chosen and where should it be located.

Boiler type

There are various types of domestic boilers available and the type best suited to any application must depend on the particular circumstances involved. The choices available are as follows:-

Room sealed or open flue

Gas boilers are available in either room sealed or open flue form. Normally a room sealed boiler is preferable, but in extreme cases, there may not be a position for a room sealed terminal. With the open flue type, the flue system is "open" to the room at the boiler and the air for combustion is taken from within the room. Additional air is also entrained from the room into the draught diverter to dilute and cool the products of combustion coming from the room. In a room sealed boiler, the flue is sealed from the room, and all air for combustion is taken from the terminal position outside the property. It should be noted, that open flued boilers are becoming more difficult to obtain, as modern designs of boiler can accommodate almost all domestic circumstances.

Natural or forced draught

Free standing or wall mounted

Combi or traditional

Condensing or non condensing

This is a more or less obsolete consideration, since as from April 2005 in England and Wales and from April 2006 in Scotland, all replacement boilers must be condensing boilers. When a hydrocarbon fuel is burned, the gasses produced as a result of complete combustion are Carbon Dioxide, Water (steam) and nitrogen. In a traditional Boiler, the water (steam) in the combustion products does not present a problem, as it is so hot it is still in gaseous form (steam). Therefore no allowance is made in the boiler design to cope with water in the combustion chamber. A condensing boiler, however, is so efficient and the exhaust gasses so cool, that the steam starts to turn to liquid water(condenses), thereby releasing the latent heat of condensation, thus giving the boiler efficiency a further boost. Because of the requirement now to deal with this water formation, Condensing boilers have to be constructed of materials resistant to corrosion, since as you would expect, the water is contaminated by other things in the flue gasses and is mildly acidic. The boilers also have a drain and are often plumbed into the homes drainage system. You can easily tell if a particular house has a condensing boiler, as there will often be a huge plume of steam coming out of the terminal. Traditional boilers also plume, but to a very much lesser extent. and this pluming occurs outside, once the gasses are expelled.

Boiler position

There are several important factors to be considered when deciding where to site a boiler. Proper fluing arrangements to dispose of the products of combustion are crucial to the safety of gas and oil appliances. The manufacturers installation instructions and british standards 5440 must be studied and followed.

In general, room sealed flue systems are to be preferred. If A Balanced Flue appliance is chosen, then the boiler must be positioned on an outside wall, so the flue can be taken directly through the wall. Nowadays, however, the varied flue configurations possible with modern fan assisted flues mean that this restraint is no longer valid, invariably, a boiler with a fan assisted flue system can be positioned almost anywhere within the property.

There are also various restraints on the position of room sealed flue terminals with respect to building features, eg. Distance from openable windows, ventilators, doors corners etc. Some guidance on the siting of terminals are given in Figure 5.

It should be noted, that the type of boiler selected and it's siting are not wholly independent considerations, since a decision on one may affect the other. Even though room sealed boilers draw their air for combustion form outside, they may still require ventilation for cooling purposes if sited in a cupboard or compartment.

Open flued boilers have so many restrictions on siting, and ventilation requirements. If You have one to replace, then for safety considerations, it should be replaced with a room sealed model.

Other considerations when siting a boiler include.