Gas boilers normally extract the air they require for combustion either from inside the heated area or straight from the outside. Extracting air directly from outside, characteristically via a plastic pipe that moves through an outside wall, is more effective and secure.

This system is generally referred to as sealed combustion, since the gas is burned in a chamber that is blocked to engaged areas. This arrangement almost removes any hazard in the event of combustion gases seeping out into engaged areas.

The efficiency of gas boilers can be greatly increased by incorporating motorized dampers that block the flue pipe outlet when the boiler is not in use. This helps in preventing the loss of heated room air between boiler cycles. Another way to increase the efficiency of gas boilers is by using electric ignition. This does away with the necessity for a standing pilot light.

Gas boiler efficiency can also be enhanced by fan-assisted combustion systems, which do not call for a very big natural draft chimney and can be relieved through a minor flue pipe straight through a wall. Gas boilers, in reality, operate best at full load. When their intensity is lessened, they can drop by as much 20 percentage points in efficiency.

If building requirements are diverse, as is common in commercial buildings, multiple boilers are considered to be highly suitable. Generally, small gas boilers that function effectively are considered a better option than the most suitable of the bigger gas boilers. As has been observed, a number of small boilers can function more competently than a single big system. The reason is that each gas boiler can function frequently close to its full load, which is the most important yardstick for a gas boiler to function in an effective manner.