Thanks for the recommendations guys and all the answers thus far are excellent. The question regarding heating the home in a PO world is very difficult to answer since our society is very much entrenched in the whole concept of using fossil fuel. Whether there can be a smooth transition to using solid fuel such as wood and coal (!) in the future is hotly debated, especially amongst us peakniks.
If you want to change your heating to be less reliant on fossil fuels then you have to ask yourself how far down the comfort road do you want to go because this will affect what you install, the cost of doing so and how interactive you will need to be with your new system. For instance, oil and gas boiler systems require very little user involvement assuming there are no breakdowns and you keep a check on the oil level (if you have oil). Solid fuel, however, requires a lot more involvement - you have to light it for a start, then check on it regularly and so on. Basically, the heating of your home will never be the same again if you switch to wood or coal.
As fischertrop rightly says, if one does convert to wood for heating, will there be enough of it in a PO world to go round? Until the carrying capacity of the planet is reduced and the population falls dramtically we will probably face severe shortages of wood in the future. My concern is that we will turn to coal which of course is a climate change issue.
OK, fossil fuels are set to rise, your current system is dying and you've decided to change to alternative heating. Here are the possibilties:
For space heating i.e, to heat your house via radiators then you can choose to install either:
1) A wood or coal (standard multifuel) burning stove with back boiler for connection to your radiators. This will burn logs and coal. This is cheap to install (?2000-3000) but less efficient than any fossil fuel system so burns more wood. If you have a large, poorly insulated, house then this might be an issue. It requires lots of user input. You can opt for a solid fuel burning cooker with back boiler such as a Rayburn, then you can cook as well.
2) A pellet boiler using wood pellets, again with a back boiler. These are a lot more efficient and are automated so require less user input. They cost more, probably around ?3000-?4000 including installation and the downside at the moment is the availabilty of the pellets which is poor. Hopefully this will change, but in a PO world the distribution of pellets might be an issue. There are boilers that will burn both pellets and logs which gets over this problem a bit.
3) A gassifying wood boiler. This is state-of-the-art technolgy with efficiencies of 90%. It burns logs very slowly (burns off the gases from the wood) and so requires very lttle input. It also saves on fuel and you can use local wood. The downside is that you normally need to connect it to a large hot water storage cylinder (an accumulator) which acts like a back boiler and heats your radiators. This pushes the cost up to ?5000/6000+ and you also need space for the boiler and cylinder which is big. Also in a PO world, will such technologically advanced boilers be a good thing or bad? Will there be the constant electricity supply needed to run this boiler and will there be the infrastructure in place for maintenance and parts etc?
4) If you think there will be no problem with electricy supply in the future then you might opt for a heat pump. This is a refrigerator in reverse which extracts heat from a pipe in the ground and puts it into your house. For every kw of electricty used it will give you 3-4kw in your home. These are expensive, starting from ?8000+ and are limited in their output (about 10-12kw normally) so you need a very well insulated house. You also need a lot of space in you garden for the pipe or you can pay the extra cost and fit it in a bore hole to save space.
For hot water (usually called dhw - domestic hot water) you can use all of the above as normal. A series of pumps, thermostats and valves will divert the heat from the back boiler or other chosen heat source and will circulate it around a cylinder of stored water (often called the immersion cylinder as found in all homes with airing cupboards). The simplest system, such as a stove and back boiler (as in 1 above) will heat the dhw cylider via gravity circulation which means that you have hot water regardless of whether you have electrcity because a pump is not needed. If, in a PO world, we have a problem with electricity supply then this will be an advantage. You can also use a solar panel to heat your water. This will cost about ?3000-4000 and will heat the dhw cylinder during daylight hours. This reduces the load on the solid fuel boiler. A solar panel will provide most of your dhw in the summer and some in the winter. You may need to have a different dhw cylinder installed with extra connection points which can be costly (an additional ?500-1000).
If your budget can extend to it then PV (PhotoVoltaic) panels and a wind turbine will give you electricty which can be used for dhw as well as lighting and electric car charging of course. These are however expensive (several thousand each) and you are reliant on decent light levels and a blowing wind.
As you can see there are several options. The issue of what is the best system therefore comes down to budget and how far you want to gurantee your comforts in the future depending on possible PO scenarios. Good insulation, warmer clothes and a few lifestyle changes will probably make as much difference. You also have to take into account what your current plumbing set up is. If you have underfloor heating for instance then changing to the wrong system can present problems, you would probably have to go for using an accumulator or heat pump as in options 3 and 4 above. It is of course hard to advise specifically in this forum. Also, the size of boiler needed depends on your house construction. A typical new build 5 bed house might only require a 10-15kw boiler where as an old C.16th house of the same size with little insulation and badly fitted windows might require 20-25kw. The prices I've given above will no doubt vary also.
Here are some web sites you might want to check out. There are loads more.
Wood boilers, stoves, gassifyers and duel fuel:
http://www.aga-rayburn.co.uk/69.htm
http://www.3genergi.co.uk/index.htm
http://www.econergy.ltd.uk/
http://www.bioenergy.org/
Heat pumps:
http://www.viessmann.co.uk/ (these do solar, wood etc also)
http://www.iceenergy.co.uk/heatpumps.html
Solar panels:
http://www.solartwin.com/
http://www.imaginationsolar.com/index.shtml
http://www.solar-design.demon.co.uk/solar/
Domestic Hot water cyliders:
http://www.albion-online.co.uk/
Click on 'products' on left menu then 'mainsflow thermal store' on right menu. This shows you options for having a cylinder with lots of coils to connect to a solar panel, underfloor heating, wood stove etc simultaneously. These cylinders also deliver mains pressure hot water so you can still have a power shower in a PO world.
PV panels:
http://www.bp.com/sectiongenericarticle ... Id=3060204
(yes this is the oil company BP)
http://www.genersys-solar.com/home.asp
Wind Power:
http://www.almac.co.uk/proven/
