Make your own hot water

It takes power to heat water. This is a basic fact of science. However, the water that goes into your houses' boiler is particularly cold, having arrived fresh from the main water supply. Therefore it takes needless extra energy to heat it up.

The alternative is to make our own hot (or at least warm) water and so save energy.


As a DIY project it is perfectly possible to heat your water by by an average 20% in cold northern latitudes without paying for power. This saving is not only beneficial to the environment but saves you a lot of money. As the cost of fuel is set to double within five years, setting up a system now could be a real investment and could increase the value of your home.

There are a number of different approaches to heating water. This article will focus on just three:

  1. Extracting heat from the ground
  2. Direct solar heating
  3. Compost based heating

Extracting heat from the ground

There are two ways of extracting heat from the ground. The first is to drill a deep borehole to a depth of between 15 to 100 metres (in general the deeper the better) and a sealed pipe loop is inserted down the hole.

A small pump circulates water and refrigerant in the pipe bringing water warmed by the ambient temperature of the ground to the surface. This warmth can then be given up to a hot water tank.

A cheaper to install although less effective method is to bury the sealed pipe just a metre or two below the surface. This requires a large garden but is certainly cheaper to set up.

Direct solar heating

Each square foot of sunlight can generate up to 100 watts, or 300 BTU of heat on a bright sunny day. Even on a cloudy overcast day about of quarter of that is still being produced. With this in mind it makes sense to investigate direct solar heating.

Popular in hot climates, a series of black pipes laid on a roof absorb heat directly from the sun and a small pump pushed water around the system. The most basic of these setups are known as Flat Plate Collectors. More advanced systems (better suited to colder climates) include evacuated glass tubes which contain a central pipe with a fluid such as engine oil. These can reach very high temperatures and are excellent when used on their own or in conjunction with flat plate solar water heaters. Read more about solar water heating.

Compost based heating

The same principle as the two systems above, but the heat is generated through the microbial activity of a large garden compost heap. This technique is known as thermophilic compost heating or bacteria fuelled heating.

In all three cases, carbon savings can be made by ensuring the electricity used to power the small pump comes from a renewable energy source such as photovoltaic cells.

Air Source Heat Pumps

These are units that use the same principles as domestic refridgerators, extracting heat from the outside air in much the same way that a fridge pulls heat from its own inside. Even in the depths of winter, Air Source Heat Pumps can extract heat from the air. A great option for powering underfloor heating systems or warm air heating (as opposed to traditional water filled radiators) They run on a small electric motor so when combined with an electrcity generator (solar panels for example) they can be remarkably cost and energy efficient. There are two types of these systems so make sure you speak to experts in installing air source heat pumps before going ahead with a project. Water source heat pumps work on a very similar principle, extracting latent heat from ponds or lakes close to your building.