From Greenhouse to Green House

The threats of climate change
CO2 emissions and savings


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Burning fossil fuels to heat water and to keep warm at home is one of the biggest sources of CO2 in the UK (and other places with cold weather). This is a much harder problem to crack than greening our electricity supply.

Until recently, we have heated the house and the hot water from a rather old-fashioned gas boiler behind a gas fire in the living room. From the point of view of CO2 emissions, gas is better than coal or oil (because it contains more hydrogen and less carbon). But we are keen to eliminate 'fossil' CO2 emissions altogether, if possible.

We have now improved efficiency by installing a modern condensing boiler and we estimate that this change has reduced our emissions of CO2 from domestic heating by about 30% (see our spreadsheet of CO2 emissions and savings). This is a very welcome saving but it would be nice if we could avoid burning fossil fuels at all.

The main options that we are looking at are described in the following subsections (CHP is one option but this has already been discussed briefly here).

Links:The Renewable Energy Centre

Don't bother

One option is simply to live in a cold house and not use hot water. Some people do this but it might be difficult to persuade large numbers of people to give up the comfort they have become used to. In any case, Britain has a scandalous record for the number of old people that die of hypothermia.

Living in a cold house would be a lot more attractive if there were good lines in heated clothing. Some motorcyclists keep warm in jackets or trousers (or both) that are heated safely by low-voltage current from the motor-cycle battery. With nice designs and improvements in the technology, something like this could be an attractive alternative to heating the whole house. Given a supply of electricity that is totally green (as described above), there would be zero emissions of CO2.

'Super' insulation

In principle, it is possible to insulate one's house so well that heat from lighting, cooking and body heat, together with solar energy, is enough to maintain a comfortable temperature (see, for example, Bed Zed). Heat exchangers are normally needed to maintain fresh air and conserve heat at the same time.

Super insulation is much easier to do with a purpose-built house. However, we think it should be instructive to see what can be done with our bog-standard chalet-bungalow, built in the 1960s when fossil fuels were cheap and climate change was barely heard of. 

We already have rock-wool cavity wall insulation and there is some insulation in the roof. But something radical is probably needed to make a big cut in heating. This probably means external insulation. Putting thick layers of insulation on the inside uses up valuable living space and it is liable to leave cold spots. External insulation has the advantage that the walls act as a heat store.

Here are some of the problems we anticipate in retrofitting super insulation to the outside of a house like ours:

  • If we were to add external insulation of the sort of thickness that is used in the demonstration building at the Centre for Alternative Technology - about 1 metre - then there would be very little left of the paths around the house. This would not matter at the back and front but on each side, our neighbours' fences prevent us taking any more space. We could only manage insulation up to about 300 mm at the sides. An interesting development in this connection is the use of insulation panels from which air has been evacuted (see Vacuum Insulation). Apparently, this increases the level of insulation quite substantially which means that thinner insulation panels may be used.
  • This kind of insulation would alter the appearance of the building substantially. It is likely that this would cause problems with existing planning regulations and practices, which are rather conservative. The Government needs to ensure that planning authorities will not prevent this kind of insulation being added to existing buildings, with possible exceptions for buildings with special historic significance.
  • We would anticipate adding one or two additional layers of glazing to each window at the level of the new external face of the wall resulting from the addition of insulation. We have not so far been able to discover any commercial system that will solve this problem.
  • Because our roof space contains rooms, it is not possible to add thick layers of insulation in the way that would be possible if the loft space were empty. There is some insulation between the ceiling and the tiles but there is a limit to what can be put in there. If we are to achieve super insulation, we probably need some kind of external cladding that can be laid on top of the existing roof or we would have to remove the tiles, lay insulation on top of the beams and fix the tiles to the insulation. We have not so far been able to discover any commercial system that will solve this problem.
  • While it should be possible to add insulation under the ground floor where there are suspended floors, some of our ground-floor rooms have solid floors and insulation could only be added by removing the concrete..

In general, there is a need for 'systems' that can be retrofitted in a flexible way to existing houses of many different designs. We believe the Government should take steps to ensure that systems of this kind are developed and made available for purchase by individual householders.

If the stock of existing houses in the UK is to be insulated up to the standards that are now needed, the Government will need to provide very large subsidies to bring down the cost to individual householders.

Links: Old Home SuperHome, Webcast about the passive house concept from Leonardo Energy, Passive House Solutions Ltd, Vacuum Insulation, Passive House Institute, PassivHausUK, Permarock, Sto external wall insulation, Envirowall, Thermafleece, INCA, KnaufInsulation, Roofing Solutions UK.


Burning fuels derived from plants means that there is no net release of CO2. Possible fuels include logs, wood chips, wood pellets (see below), agricultural waste, biogas, biodiesel and vegetable oil (see below), and newspaper briquettes. Although peat originates from plants, it is really a fossil fuel and there are other environmental reasons not to destroy yet more peat bogs.

A particular problem with biogas is that it cannot be liquefied like LPG. It can be stored under pressure but this is cumbersome and not entirely safe. Consequently, it does not look like a good option for domestic heating. That said, we are interested in the Greenfinch Biowaste Digester, generating biogas (methane) from kitchen waste and the like.

For biofuels to be truly green, it is necessary for them to be produced and transported with zero CO2 emissions.

If biofuels are to be adopted for domestic heating, they will need to be as cheap as fossil fuels or cheaper.

Costs of biofuels compared with conventional fuels.

Links: Rika Stoves (pellet stoves).

Heat pumps

It is possible to move heat from the outside of a house to the inside using a heat pump that works like a fridge in reverse. The heat can come from the air or from pipes buried in the ground.

If the pump is run on green electricity or something like biodiesel, then zero net CO2 emissions can be achieved. The main attraction of heat pumps is that the amount of energy needed to move heat from one place to another is relatively small compared with the energy in the heat itself (about 1:4).

This is all proven technology and sounds attractive but there are few suppliers of heat pumps for domestic use in the UK.

Although some installations attract VAT at 5% (compared with the normal 17.5%), there is a need for the market to be given additional encouragement by tax incentives and/or grants.

Links: Kensa Engineering, GeoScience Ltd, Heat Pump Association (UK), UK Heat Pump Network.

Solar water heating and passive solar heating

Solar water heating

In the summer of 2005 we arranged for a Solartwin solar water heater to be installed. This is a neat design that is significantly simpler than some other systems. It is designed so that freezing causes no damage and it includes an electric pump powered by a small photovoltaic solar panel so that there is no need to use mains electricity which may have come from non-renewable sources.

A grant of £400 from clearskies meant that the net cost to us was about £2,200. The panel is mounted on a roof that faces south-west, which is not quite as good as due south but apparently gives 95% of what one would expect to get if it did face due south.

We are very pleased with this device. Most of the time we do not use the gas boiler to heat the water. During the summer, we get quite a lot of hot water, mainly when there is direct sunshine. When there is direct sunshine during the winter, the water is heated to a pleasantly warm temperature which is quite suitable for many purposes: washing one's hands, washing dishes, cleaning floors etc. If we need water that is hotter, then we use the gas boiler for a short time to give just enough hot water for what we need.

Passive solar heating

Passive solar heating works best when a house has been purpose-built to take advantage of the sun. With an existing building, it is possible to get some solar heating from a conservatory or from areas of glass covering south-facing walls or roof or both.


Electricity generated inefficiently from fossil fuels or dangerously from nuclear power is a poor option for domestic heating. But electricity from wind power or other renewable resources is worth considering. At present, it is rather expensive for space heating or water heating but this may change.

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