Combination Boiler Explained

Oil Fired Combination Boiler – Combi Boilers

Combination boiler are commonly called combi boilers, and are similar to a conventional boiler with a second heating circuit which instantaneously produces hot water. Often overlooked is the fact that the operating / engineering differences between gas and oil fired combi boilers is significantly different.

Oil fired combi’s, unlike gas, do not have modulating burners to cope with additional heating demand when a hot tap is opened. This problem is addressed in two ways: – an integral water store making them physically big. – a larger boiler output than is actually required to satisfy central heating demand; you might end up with a 30kW boiler where a 20kW conventional boiler would suffice and also be more efficient. When the heat store is exhausted, hot water flow of 10-13ltrs / minute @ 35^oC rise above mains temperature is around the norm. To fill a bath (112ltrs) will take about ten minutes, provided no other taps are opened.

High life-time costs…unlike a gas combi, water is stored in the boiler at circa 80^oC, components subjected to this constant residual temperature will fail. Oil fired combi boilers are complex, have bespoke components; they will be more expensive to maintain than a conventional system. Good business for boiler manufacturers, not necessarily the best option for the homeowner!

So what’s the solution? Keep it simple! In so many cases a conventional boiler with a pressurised domestic hot water cylinder such as a Megaflow is a far better option. The benefits: – loads of hot water at mains pressure – up to 72 litres per minute – back up immersion heater – industry standard components