5 minutes min

Heat and insulation, how does it actually work?

Everyone needs heat in our houses to not freeze and to have a nice and comfortable indoor climate. How much is needed depends on the outdoor temperature, but also how well the house is about retaining the heat already available. 

This with heat, insulation and heat transfer is not always easy to understand. Here you will get a quick idea that will hopefully give you an insight into how things are all together.

How much is a kWh?

Kilowattimme (kWh) is a measure of the amount of energy you use, regardless of the heating method you selected. A kWh corresponds to the amount of energy required to heat 10 liters of water from 0 ° C to 100 ° C.

  • 1 m³ of oil corresponds to 10,000 kWh
  • 1 m³ of wood corresponds to 1,630 kWh
  • 1,000 kg pellets correspond to 4,700 kWh

Heat and different materials

Heat is a kind of motion energy where the molecules vibrate in an unstructured manner. The faster the movement, the higher the temperature. Heat is stored in material and different materials have different storage capacity. For example, water has very good heat storage capacity while air is significantly worse. Temperature changes can occur different fast or slow in different materials. In a house with heavy stems, such as a church with thick stone walls, temperature changes are very slow, which can be positive in a way. But it takes a lot of energy and takes a long time to raise the temperature again after the house has cooled down.

Heat insulation and heat capacity

In the case of houses, it is important to distinguish between the building's thermal insulation (ability to keep the heat inside the house) and heat capacity (ability to store heat in the walls). Imagine a stove that is covered with soapstone and another stove that is insulated. The soapstone stays the heat for a long time and simultaneously leans the heat to get it part of it. A soapstone stove thus has high heat capacity, but requires constant supply of woodclips because the heat is "consumed". On the other hand, a stove with insulation keeps the heat inside the stove, which means that it does not work so much, it has good thermal insulation. On the other hand, you will not get a part of the heat.

Transfer of heat

If there is a difference in temperature between two materials (matter), nature strives to equalize this difference. The natural displacement of heat takes place from higher to lower temperature. This transfer of heat can occur in three different ways; through conduction, radiation and convection.

Central heating

In solid materials, such as metals, heat is transferred from hot to cold part through wire. Even liquids and gases lead heat, but radiation and convection also plays a big role. As a comparison, it can be mentioned that aluminum conducts heat approx. 10,000 times better than stagnant air.

Heat radiation

Heat radiation (infrared radiation) occurs in liquids and gases as well as in vacuum. A common example of radiation effect is when you experience certain places as draggy. Then it's actually your body that emits radiation heat to the cold surface, for example in a window.


There are two types of convection, self-convection and forced convection. Self-convection (natural air movement) may occur in gases and liquids when subjected to a temperature difference. Because hot air (gas) is lighter than cold, the hot air rises. The air moves and comes into contact with colder surfaces, cools and falls. Through this process, the heat can spread far. Forced convection is caused by winds, for example, differences in air pressure. For example, it is important to have a windscreen on the outside of the outer wall body.

How does insulation work?

On the market there are several different insulation materials and most have a good thermal insulation ability. The design is made to make it difficult for the heat to transition from the hot side to the cold. The reason is a "skeleton" that looks a little different depending on what material it is; for example stone wool & glass wool. Between this "skeleton" is a gas that is usually air.

The role of isolation is to balance the three heat transfer modes. The fibers in the stone wool are long and thin which impairs the heat conduction (wire). By having many fibers, there will be many fiber walls (barriers) in the insulation which reduces the risk of heat radiating directly from the hot side to the cold (radiation). The fibers also keep the air still and minimize self-convection (hot air rises, cools down to a colder surface and decreases) (convection). To describe the amount of heat passing through a material, the term thermal conductivity (thermal conductivity) is used. It is called λ (lambda) and is often called lambda value.