Primary Energy Sources
Selecting a source of heating is a balance of cost, convenience, efficiency and reliability, and the energy cost of heating is one of the main costs of operating a building in a cold climate.
- Solid fuels such as wood, peat or coal can be stockpiled at the point of use, but are inconvenient to handle and difficult to automatically control. Wood fuel is used where the supply is plentiful and the occupants of the building don’t mind the work involved in hauling in fuel, removing ashes, and tending the fire. Pellet fuel systems can automatically stoke the fire, but still need manual removal of ash.
- Liquid fuels are petroleum products such as heating oil and kerosene. These are still widely applied where other energy sources are unavailable. Fuel oil can be automatically fired in a central heating system and requires no ash removal and little maintenance of the combustion system. However, the variable price of oil leads to erratic and high prices compared to some other energy sources.
- Natural gas is a widespread heating fuel in the UK. Gas burners are automatically controlled and require no ash removal and little maintenance. However, not all areas have access to a natural gas distribution system. Liquefied Petroleum Gas (LPG) or Propane Gas can be stored at the point of use and periodically replenished by a truck-mounted mobile tank.
- Electric heating can either be purely resistance-type heating or make use of a heat pump system to take advantage of low-grade heat in the air or ground. Some areas have low cost electric power, making electric heating economically practical.
Calculating the Output of Heat
Heater outputs are measured in kilowatts (kW). For placement in a house, the heater required for the house needs to be calculated. This calculation is called a ‘heat loss calculation’. Depending on the outcome of this calculation, the heater can be exactly matched to the house.
Factors such as the number of outside walls, the size of windows and whether they are double glazed, the age of the home etc, can all influence the heat requirement. As a rough initial guide, to achieve a relaxing room temperature of around 21ºC when the external air temperature is at freezing (0ºC) you will need approximately 1kW of heat output for every 14 cubic metres of space.
To work this out, measure the length, width and height of your room and multiply the three figures together and divide by 14 to arrive at the kW output required. For example, a room measuring 7m long by 4m wide and with a height of 2.5m is 70 cubic metres of space. Divide by the sum by 14 and this means you will require a 5kW stove.
From an energy efficiency standpoint, considerable heat is lost or goes to waste if only a single room needs heating, since central heating has distribution losses and may heat some unoccupied rooms without need. In buildings which require isolated heating, you may wish to consider non-central systems such as individual room heaters, fireplaces or other devices. Alternatively, architects can design new buildings which can virtually eliminate the need for heating, such as those built to the Passive House standard.
If a building does need full heating, combustion central heating may offer a more environmentally friendly solution than electric resistance heating. In contrast, hot-water central heating systems can use water heated in or close to the building using high-efficiency condensing boilers, bio-fuels, or district heating. Wet underfloor heating offers the option of relatively easy conversion in the future to use developing technologies such as heat pumps and solar combi-systems, thereby also providing future-proofing.
Typical efficiencies for central heating, measured at the customer’s purchase of energy, are: 65-97% for gas fired heating; 80-89% for oil-fired, and 45-60% for coal-fired heating.