Heating accounts for the largest use of energy in the home.
The Ideal Solution
In terms of impact on the environment, the most effective way to heat a building is use low-carbon energy sources rather than gas, oil or electricity which all contribute to carbon emissions. With current technology the very best one could do on a house is to have a wood or pellet fired boiler, a ground source heat pump or a heat exchanger, any of which would provide space heating and hot water. To this could be added solar hot water panels for hot water primarily in the summer months. If these were combined with the best insulation measures possible, the energy derived from fossil fuels needed to heat the house would be minimal, as would be the CO2 impact of the house. Heating costs would also be very small.
The Difficulties
However, all these options are expensive and in many cases impractical. It becomes disruptive internally because all these space heating options require some kind of low temperature heating system such as underfloor heating, skirting heating or large panel radiators. They are most suitable for houses being completely gutted and refurbished or for new build properties.
Wood or pellet fired boiler
I decided not to go with a wood burning stove with a back boiler mainly because of cost and the difficulties of making storage space for the fuel (pellets or wood). There is also the question of getting reliable supplies of fuel. A potential difficulty might be in reselling the house or letting it to tenants who are happy with this kind of heating - it requires a little more planning and thinking about. Wood and pellets need to be ordered and a check kept on levels of fuel. So many people are used to just turning on the gas without needing to think about it.
Geothermal ground source heat pumps and heat exchange systems
These are not suitable technologies for a project like this. Geothermal ground source heat pumps are difficult to install in an urban setting and expensive. A heat exchange system is also very expensive to install and the technology is not really geared up to small scale domestic systems. They can work well in larger scale projects.
Conventional heating fuels
In terms of conventional heating sources most CO2 emissions come from electricity production, almost double the emissions of oil and gas. It therefore makes sense to use either of the last two if the cost of renewable technologies is too high. Gas is still the cheapest conventional fuel but this may change rapidly as supplies run low. This house has a gas supply.
Boilers
There are combi boilers and boilers that feed a hot water storage tank. Combi boilers provide instantaneous hot water on demand and many people claim that this is more energy efficient than heating a tank of water that may then not all be used. This applies particularly in smaller houses and flats. Storage system boilers need space for a cylinder. For information on domestic hot water systems see DIY doctor.
 This house has a combi boiler which, although not a high efficiency boiler, is not that old. Because it is a combi boiler, there is no hot water cylinder in the house which means also that there is no airing cupboard (hot water cylinders however well lagged always seem to give off heat which can be useful). The two following headings look further into the pros and cons of changing the boiler and the heating system.
Solar thermal panel for hot water
This is probably the most tried and tested of the renewable options for domestic use and for most people there are grants available. However, if you are not eligible for grants, the cost is high unless you feel able to do a DIY job. At our own house, we have had one for years and it means we can turn the boiler off for most of the summer months with the occasional boost on cold days. It is completely hassle-free and only uses a tiny amount of electricity to run the pump.
Solar thermal panel
 Water is pumped through efficient panels on a roof where it heats up and is taken into a hot water cylinder where it is stored until it is needed. Controls ensure that the water is heated up to the proper temperature using another fuel source, such as a gas boiler. Even on sunny days in winter the panels warm the water and so less energy is needed to get the water up to temperature. In summer the water can get blisteringly hot.
The problem with this house is that there is no hot water cylinder and, in order to put in a solar thermal panel, you need a cylinder to store the hot water generated. Combi boilers can be made to work with solar systems but most plumbers advise replacing the boiler. It means the overall cost of installing a solar thermal panel is high (cost of cylinder, boiler and pipework as well as solar panels), although it would give me the opportunity to upgrade to a modern high efficiency condensing boiler with consequent further CO2 savings.
Condensing boiler, controls and radiators
The energy reports and advice I have on the house do suggest that it is worthwhile replacing the boiler even now because the CO2 savings are very good. However, I find it hard to accept it is right to replace a piece of machinery that is working well and not very old.
By law now if you have a new boiler you have to fit a condensing boiler. These are much more efficient than older models. I have been recommended a weather compensating boiler (see Viessmann), which sets the temperature of the boiler with reference to the outside temperature and removes the need for a thermostat in the house.
The inside control would be via the individual radiators which I have fitted with thermostatic radiator valves, plus a new digital thermostat and timer. I had also intended to put heat reflecting panels behind the radiators to improve the heat thrown out into the room, but again ran out of time.
Wood burning stove
The coal effect gas fire in the sitting room gave out negligible heat and looked tired and old. We removed this and rebuilt the fireplace with some old bricks, a piece of salvaged oak for a
lintel and some new paving slabs for the hearth.
I installed a log burning stove (a Stovax 4kW Clean Air Act Approved stove) but it was expensive because the chimney needed a liner. The prices of wood burning stoves have rocketed over the last year or so and I suspect they will continue to rise. It seems to me to be worthwhile to install one because in a house like this it could really make a difference in supplementing the gas heating. It does mean building a log store (not yet done) and explaining to tenants or purchasers how to use it well.
Thanks to our district council, I received a small grant towards the cost of installing the log burner.
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Heating
