In almost all modern homes the most energy is used to keep the room temperature on the desired level. It includes both heating in winter and air conditioning in summer. In some climates you need only one of those, in temperate climates you need both. For example, in Poland we have annual mean temperatures close to 6-10°C (43-50°F): in winter it easily drops to -25°C (-13°F) and in summer it may reach +35°C (95°F) (1). So we need to warm our homes and sometimes to cool them using air conditioners. In addition, we need to warm our domestic hot water supply as we like to bath in hot water. 😉

In winter, energy is lost from inside the building to the environment. In summer, the heat flows from outside to the building. To minimize the amount of energy required to control the climate in the building, we need to insulate it. If you desire to make your own heat and cold, you first need to insulate your home as good as possible.

In typical case, you have your house warmed by central heating system (furnace + heaters), stoves, electric heaters or heat pump. Luckily, there’s a lot different sources of free energy to use it for climate control.

First of all is the most important — solar energy. Solar heating may be used to reduce a lot of energy usage. In passive houses thanks to large windows exposed to southern direction (to get as much sunlight as possible) total energy usage for heating is reduced to 15 kWh per square meter (3) (equivalent to ca. 51 000 BTU per square meter, roughly 1/3 of a gallon of heating oil per square meter (2), ca. 4700 BTU per square foot, 1/30th of a gallon of heating oil per square foot). In european conditions, close to what I described above for Poland. Solar thermal collectors are used to produce solar hot water, but they work mostly in summer. In winter their thermal output is greatly reduced. In warmer climates, like in the mediterranean (4), solar heating with heat accumulation may supply all the energy required in winter.

Second good energy source for heating is the biomass. Burning biomass (wood, biogas, rice husks, etc.) leaves no carbon footprint and thus it is considered to be renewable and sustainable. You can make your own fuel for your furnace, if you have a piece of land big enough for salix viminalis willow or panicum virgatum switchgrass.

Both solar energy and biomass may be also used to refrigerate and chill air. If you use absorption cooler, instead of electrical energy you use heat to generate cold.

In future articles in this category we’ll discuss the possible energy sources for heating and air conditioning.


  1. Climate of Poland at,
  2. Heating oil at Wikipedia,
  3. Passive house at Wikipedia,
  4. Mediterranean climate at Wikipedia.