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FOR HOUNSFIELD BOILERS

A non-condensing boiler is similar to condensing boilers except they do not have a stainless steel secondary heat exchanger.

A modern non-condensing boiler running on oil will be around 4% less efficient than an equivalent condensing boiler model.

When installing non-condensing boilers, a Building Regulations exemption is required, please refer to our installation guide documents.

Combination boilers, commonly called combi boilers, are similar to conventional boilers 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°C rise above mains temperature is around the norm. To fill a bath (112ltrs) will take about ten minutes, provided no other taps are opened.

What are the problems with oil combi boilers?

High life-time costs…unlike a gas combi, water is stored in the boiler at circa 80°C, 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! This is why Hounsfield Boilers do not manufacture combi boilers.

So, what’s the solution?

Keep it simple! A wall mounted or external oil-fired boiler with a small 70ltr 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 @ 3 bar vs 10-13 litres for a combi boiler. An immersion heater for back-up if you run out of fuel and industry standard components provide for low life-time maintenance costs.

Read more Are Oil-fired Combi boilers a compromise

System boilers are designed to reduce installation time, they contain all the heating system components within the boiler casing, a circulating pump, pressure relief valve, and expansion vessel.

The expansion vessel is often undersized, simply to fit into the boiler casing rather than suit system water capacity.

Residual heat in the mass of an “oil fired system” boiler will cause components to fail, making system boilers expensive to maintain. This is why Hounsfield Boilers do not manufacture system boilers.