Listed building near Farnborough Village, Kent

The brief was to replace an old Potterton boiler in the basement with a new unit, and make the system more efficient.  Spread over 3 floors and a cellar, this building is Grade 2 listed, and therefore represents a challenge when alterations to building services are required.

The house is bigger than it looks

We looked into replacing the boiler in the cellar with a modern condensing unit, and relining the chimney.  However, there were adjacent chimney pots that were in use, and also there were plans for the cellar which meant that our customer would prefer the boiler to be resited to an otherwise unused store room half way up the cellar stairs.

Our design used a new Worcester-Bosch Greenstar 40CDi boiler, with a flue system that was directed sideways through an old toilet and then vertically through a void to a pitched roof terminal.  The local conservation officer gave full approval to this solution.

New boiler position, glanced through window in off cellar stairs room. Lots of boilers on here, trying to make it more interesting….

Our roofing specialist inserted the new boiler flue into the aged roof of an extension to the original building

The existing heating solution used a number of pumped circuits for heating and hot water, so we linked these into a distribution header in the cellar.  This enabled us to use a device called a Low Loss Header, more common in light commercial applications.

New header (preinsulated) to enable new boiler to interface to old heating and hot water circuits

The Header enables the boiler to always have the correct amount of water passing through it, irrespective of the load attached.  It also has other benefits no so widely published;  it enables more efficient air separation because it involves a large mass of water, so the velocity slows – allowing air bubbles to separate and rise into a separator vent.  It also lowers the thermal shock on the boiler, giving less on/off periods and allows the heating pumps to run more efficiently because they are not restricted by the resistance of the boiler heat exchanger.

The header allowed us to link up to all the old pipework and multiple pumps with very few changes. NB: The timer is left over from the old system and is temporary whilst Evohome is fitted.

I expect you are bored now, but there have been a number of products launched in the last 10 years claiming all manner of savings and benefits to domestic heating systems, all derivatives of a low loss header.  In other words, there has been a lot of smoke and mirrors trying to repackage an old idea as something new.  This header was made by Bosch, but in the past we have used other makes or designed our own, depending on the application.

Back to the Gallery, and we used the new Colour Honeywell Evohome to split the house into 12 separately temperature (and time) controlled areas of heating.  All this is controlled from the Honeywell touchscreen, and also any iPhone, iPad, or ‘Android’ based device.

12 zone heating (and hot water) from one simple device. Listed buildings owners need not live in the dark ages

The existing hot water system was retained, and linked to the Evohome touchscreen.  If our customer decides they would like an unvented hot water (ie: mains pressure) system, this can easily be added later.

None of the existing radiator pipework or flooring outside the cellar needed to be altered, but now the heating can be controlled as accurately (probably more so) than a Grand Designs ecohome.

There were a large number of radiators in this job; all needed a radio controlled valve. Programming underway – each is wireless and will be assigned to one of the 12 zones.


Some of the radiators were 30yrs old; the owner had only just moved in and the decorator hadn’t got this far. This shows one of the Evohome actuators attached to a radiator.

I’ll leave you with a thought.  This house, like most older properties, takes over 80% of the annual gas bills to heat the rooms, and under 20% to heat the hot water all year round.    Since only 15-20% of your gas bill is used to heat your bath/shower water,why is everyone trying to sell solar panels, heat pumps, thermodynamic panels to do this?  Why aren’t they looking at the 80% problem?  Evohome looks the 80% straight in the eye.