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3 Acorns Eco-audits

Email: contact@3acorns.co.uk

Phone: + 44 (0)20 7703 8748

Inspiration  Information  Implementation

Mobile: + 44 (0)7947 884 299

3 Acorns Retro Eco-House

The world famous house is open to the public for free every year as part of London's architectural Open House Weekend. At other times of the year, visits for groups or individuals can be arranged - contact us for fee details.

For press visits to the Retro-eco House see our press contacts page.

Such visits can include a talk and Q&A with the owner and founder of 3 Acorns Eco-audits Donnachadh McCarthy FRSA

Donnachadh firmly believes that environmentalists should practice what they preach. He has therefore converted his 1840’s Victorian terrace home into a retro-eco home. It has solar electric panels, solar hot water panels, a rain-harvesting system, wood–burner, wind-turbine and catalytic converter gas fire.

While it is essential to a low carbon home to use the home efficiently and ensure all the basics such as insulation and energy efficient appliances are in place, certain technologies can help.

Since 2003 the house has been a net exporter of electricity but in 2006/7 Donnachadh achieve his dream of a not only a carbon neutral home but it actually become climate positive i.e. it is carbon negative exporting more green electricity to the national grid than it imports fossil fuels (gas)

It has now been carbon-negative for three years.

The environmental statistics for   06/07,  07/08 and   08/09 can be found on our Eco-Performance Page.

*(Average UK household carbon footprint = 6 tonnes (6,000 Kg))

Water Consumption

  28 litres of mains-water per day.

  (London average mains water consumption = 160 litres per day)


Non-recycled Waste Production

  Donnachadh ended up in 2006/7 being a net importer of waste!

  Domestic non-recycled waste: half a wheelie bin for entire year

  Building waste: 3 wheelie bins for year

  Imported Waste Wood for wood burner: 48 wheelie bins for year

  Net Waste IMPORTED !! : 44.5 wheelie bins

Eco-technologies used in the 3 Acorns Retro-Eco House:

Solar Electric Panels

   The house was the first private home in London to export solar electricity from the roof to London Electricity in 1997.


   The 1.2 kW rated system was installed by Sundog Renewables. In 2006/7, the house exported about 20% more electricity to the national grid than it imported.

    Following EDF energy’s energetic lobbying of the UK government to promote a catastrophic new generation of nuclear power stations, he is switching to exporting his green electricity to Good Energy’s micro-generators scheme.  Link to Good Energy's Homepage

   The display on the right shows how much electricity the roof is producing, how much is being imported or exported and how much the house is consuming. In 1997 the system cost about £12,000.  Solar electric systems today cost about the same but produce twice as much electricity.

Solar Hot Water Panels and System

   The solar hot water system was installed 2 years ago and supplies about 70% of the household's hot water needs. The vacuum tube heat exchanger system was installed by Southern Solar.

    In summer the system produces far more hot water than is needed and the temperature has to be regulated to prevent it from becoming too hot!

   The system cost about £4,200 but a £400 grant from the LowCarbonBuilding Programme and £500 from the local council brought the cost down.

Catalytic Converter Flueless Gas Fire

Unlike open coal-effect gas fires which are less than 20% efficient and traditional radiant gas-fires which are about 65% efficient, flueless gas fires are extraordinarily 100% efficient.

Using an embedded catalytic converter, all of the gas is converted to heat, with water being the only by product. This means that they are only useful in houses which have central heating in the background or have a regularly used wood stove, as these dry out the resulting condensation.

In my house, whilst very rarely used since the installation of the wood burner, it acts as a very handy back-up system in case I am ill and cannot use the wood burner or if in the house for a quick half hour before going out again and I need a burst of heat.

They cost about £500 and I got mine from Burley’s.

Rainwater Collection Systems

The toilet in the bathroom and a designated tap are supplied by a simple gravity fed rain-harvester system, which sits on the flat roof immediately above the bathroom. It has supplied over 70% of the WC water needs since it was installed 9 years ago. The main legal requirement for such systems is that the rainwater cannot mix accidentally with mains-water and so special valves are required if you want the system to be backed up with the mains.

The garden water needs are supplied from a tank that collects rain water from the lower roof run-off.  It is now quite old but still does the job, with its own tap.


Three Acorns Retro-Eco House was the first house in London to gain planning permission for a grid-attached building mounted domestic wind-turbine. It was installed in November 2005 but has not been a success to date.

It produced a recorded 16kWh last year, which is about £1.60 off the electricity bill. There have been no noise complaints from neighbours, which is great, but there is currently a vibration problem internally in the house.

StealthGen, the providers, continue to experiment with the product and the jury is out as to whether such small urban wind-turbines will make a worthwhile contribution in the future, even if some pessimists rule them out completely. It cost £2,800 installed.


Last, but by no means least, 3 Acorns Retro-eco House has a wood burner in the open plan living room/dining room/ kitchen area. This is by far the greatest contributor to reducing the energy carbon footprint of the house. People often forget that electricity consumption on average is responsible for only 30% of the average house’s carbon footprint, whereas space and water heating account for the other 70%.

I got mine from UK manufacturer Clearview Stoves. It cost about £800 plus £2,000 for installation and new chimney flue.

Visits / Talks at 3 Acorns Retro Eco-House

Whilst not normally open to the public (except for the London Open House Weekend Event in September), it is occasionally available for site visits/seminars for small groups of council planners, councillors, energy consultants and other such interested groups.

Please email contact for rates and further details.

Groups who have been on arranged visits include:

   London Energy Managers

   Kent Councillor Group (Scrutiny Committee)

   Westminster Planners

   Southwark Councillor Group (Scrutiny Committee)

   Lambeth Cyclists

Links to Related Articles

Generating interest in wind power

How a south London man went about getting his own domestic turbine in an attempt to get others to follow suit. (BBC News Online 25.10.2005)

Turbine pioneer's dream realised

An environmentalist who was the first Londoner to apply to have a domestic wind turbine on his home finally realises his dream. (BBC News Online 24.10.2005)

My London: Green house effect

A south London man tells BBC News Online how he turned his London house into an environmentally friendly home. (BBC News Online 10.11.2003)

Why concrete gardens are growing

Turning your front garden into a parking space may add value to your home, but at what cost to the environment? (BBC News Online 08.09.2005)

Rain stops drain on water supply

A council says all new buildings should have rain-catching devices to be more environmentally friendly. (BBC News Online 04.07.2004)