The condensing combi is virtually the boiler of choice in the domestic arena, making the hot water storage cylinder virtually obsolete. However, Ravenheat believes the cylinder could be on its way back - and the hot water is free. Paul Braithwaite tales to Louis Pickersgill, managing director.
LOUIS Pickersgill, managing director of Ravenheat, believes the cylinder - used in conjunction with the company's latest heat exchanger and a condensing boiler - will save up to 90% of the cost of domestic hot water during the winter.

He says his company has managed to harness the flue gases from a condensing boiler, put them through a heat exchanger, and gravity feed a storage cylinder above the boiler with free hot water.

He and his team at Ravenheat invented the system. They began by looking at attaching a solar panel to the boiler to cut heating costs further.

But it was the small amount of solar gain during the winter which moved the team to look at other ways of generating cheaper heat.
They quickly realised that one source of heat and pollution that had not been addressed by designers was that which escapes to the atmosphere through the flue.

Pickersgill insists that, with the boiler running, these flue gases can exceed 60˚C - and until now they have gone straight up the chimney.

Reclaiming heat

Ravenheat's Energycatcher is a small heat exchanger unit with a 0.75m2 surface area, which requires no electrical connections and
sits on top of the boiler.

At the Ravenheat Leeds offices, an Energycatcher unit had been built on to the Ravenheat CSI 120 and connected to a 60l cylinder.

The boiler's flue gases, instead of going straight out through the wall, are fed into the Energycatcher where they flow over a heat exchanger.

This otherwise wasted heat is transferred to the water in the heat exchanger and is then moved under convection into a storage cylinder above.

Pickersgill says the cylinder can be of any size according to the needs of the household. When the central heating has run for an hour, a large cylinder will be fully heated and give a good supply of hot water. And, of course, this hot water is free.

Suppose the householder runs the central heating system in the morning so that the house is warmed when the family get up. All the time the boiler is running the waste heat in the flue is being transferred to the water in the heat exchanger, which then passes to the storage cylinder. This water can reach between 40ºC and 50ºC.

When the hot tap is run, the water can run directly from the storage tank, via a blender valve, to the tap. This hot water is supplied free of charge. Alternatively, it can be cycled through the boiler, where the higher than normal inlet temperature is sensed and only sufficient heat applied so as to bring the water up to the normal, pre-selected outlet temperature.

This means less gas is used to supply this piping hot water. Either way, the householder saves money.


Indeed, Ravenheat estimates that, during a year, a typical gas bill will be cut by at least 5% - about £110 a year for a three bedroom detached house - against a Band A condensing boiler.

He adds the cost of domestic hot water is reduced by up to 90%.
This means overall that, by introducing the Energycatcher, a SEDBUK A boiler is converted into A+ which is the equivalent to the difference between Sedbuk D and A.

Additional benefits

The hot water flows from the tap sooner than normal, so less cold water is wasted waiting for the water to run hot, giving further savings.

As for the installer, the Energycatcher is simple to fit, uses no electricity, has no running costs and requires no maintenance, says Pickersgill.

The Energycatcher can be used with any condensing boiler but the installer must check with the manufacturer before adding the unit because of the heat of the water going into the boiler.

Although the heat exchanger works in this case with the water heating up and rising into the cylinder which is above the unit, a small pump can also be used in a flat or bungalow where there is not enough room above the boiler.

The Energycatcher can also be used in conjunction with a solar thermal installation to save even more money.

Pickersgill says that, while solar produces a boost to water temperatures when the sun shines, Energycatcher comes into its own whenever the boiler is used to heat the home or provide domestic hot water.

Energycatcher is, however, far less costly to install. Payback on the cost of a unit and a cylinder is between two and three years. And the added environmental bonus is that the exchange of heat means the used exhaust gases become too cold to vapourise and discharge in the form of ambient water.

Pickersgill also explains that the units with a bigger cylinder (or cylinders) could be used in commercial and industrial areas where condensing boilers are cascaded together to provide heat and hot water for buildings.

www.ravenheat.co.uk