Boiler is the key component of a heating or hot-water system. Boiler type defines the effectiveness of the whole system, that is why its selection is not a matter to trifle with.

So, which kinds of boilers exist and what do they differ in from each other?


There are following boilers according to their compatible fuels:

1. Gas boilers are among most popular for residential premises. These are fed by natural or liquefied gas and can be components of heating and/or hot-water systems. The latter characteristic is the criterion to divide them into single- and double-loop boilers, respectively.

The boilers can be classified by the exhaust gas emission method as follows:

  • Forced draught boilers do not use indoor air and therefore do not need continuous ventilation.
  • Natural draught boilers emit the exhaust gases though uninterrupted inflow of fresh air from the ambient, which makes them inappropriate for living premises.

Gas boilers can be classified by energy recycling as follows:

  • Condensing boilers use both gas combustion energy and condensation energy
  • Convection boilers use only fuel combustion energy

2. Solid fuel boilers use various types of solid fuel for operation and can be accordingly classified as:

  • Coal boilers
  • Wood boilers
  • Pellet boilers that consume solid combustible pellets from wood, soy, agricultural wastes, etc.
  • Combined boilers

Solid fuel boilers implement various combustion processes, namely:

  • Conventional or traditional boilers produce energy through combustion, need constant monitoring of the fuel quantity, draught, fresh air inflow, etc.
  • Pyrolysis boilers generate heat from the solid fuel combustion product – pyrolysis gas. These are efficient and effective, but require special fuel
  • Long-burning/top-fired boilers are particular for gradual fuel burning from the top to the bottom

3. Liquid fuel boilers consume fuel oil or diesel and are not used for residential buildings.

4. Electric boilers use electric power and implement the following operation principles:

  • Boilers with tubular electric heaters (TEH) to heat the medium
  • Electrode boilers contain electrodes to produce electrical discharge into the water which gets hot through electrical resistance
  • Induction boilers include induction coils and closed loops. Electricity warms up the core which transfers the heat to the water

5. Combined boilers can consume various fuels.

Installation methods

  • Wall-mounted boilers
  • Floor standing boilers

Ignition methods

  • Electric/automatic ignition boilers can automatically start in the pre-set time and resume work after a power failure
  • Manual ignition boilers


Also, all boilers differ by power.

A heating and/or water-heating boiler shall be selected according to the actual operation conditions, available fuel and other particulars.