Furnace for Heating: How to Choose

One of the reasons why people buy a stove is the possibility to use it as an alternative heating source. Is it possible to heat a house with a wood stove? Of course, you can, if the power of the stove corresponds to the heated area, taking into account heat losses, and you use an efficient heat distribution system.

But there is also a reason why people refuse the advantages of the stove as a means of heating. They can’t install them properly, even though furnace replacement service in Sacramento, CA, for example, is very affordable and fast.

 Therefore, Alphamechanicals employs specialists who have also written this article with life hacks for you.

Even the smallest power is usually enough to heat one room up to 40 m2, however, if you plan to heat several rooms with one device, you will have to choose a furnace for heating greater power and connect equipment for heat distribution. Let us consider in more detail what the thermal efficiency of the furnace depends on.

Choosing a method of heating with a furnace: air, water

Before giving the method of calculating the heat output, it is worth taking into account the number of heated rooms and the heat distribution system.

In fact, in traditional furnaces, heat is transferred to the room by radiation (radiant energy), heat transfer (air comes into contact with the heated furnace body), and convection (heated air rises higher, cold air enters in its place, thus the air masses gradually mix).

Through the open door, the heated air will gradually move to other rooms, but this will happen quite slowly, so if we try to achieve a comfortable temperature throughout the house in this way, the room where the stove is working will be quite hot, and in remote rooms – much cooler.

For the purpose of heating a larger house, a wood-burning fireplace is much better suited – in it, the heat from the fireplace is immediately removed through the air ducts to other rooms.

However, among the stoves, there are design solutions that allow you to heat the house evenly.

How do choose the furnace power depending on the heated area

If you do not use an efficient heat distribution system, do not use the area of the whole house in the thermal calculations. We advise you to count on heating the area of 1-2 rooms.

In addition, to determine the required power, you need to take into account the climate zone and the level of insulation of the house.

It is considered that 1 kW of wood stove power is designed for heating:

1. 14 m3 in a house without insulation, in a cold climate zone,
2. 20 m3 in a house with normal insulation in a temperate climate zone,
3. 33 m3 in a house with excellent insulation or in a warm climate zone.

If we take into account the average ceiling height of 3 m, we get that depending on the climate zone and the level of insulation of the house, each kW will heat from 4.7 to 11 m2 of living space.

Thus, if we install the stove in a normally insulated room of 40 m2, and plan that the heat will be partially distributed to other rooms through open doors, the power of 8 kW will be sufficient.

Rated power and efficiency of wood stoves

Power is the thermal performance of a wood stove, and shows how much heat energy can be obtained during the operation of the stove. The rated power is a calculated indicator determined in laboratory conditions during the testing of a particular model and is recorded in the passport of the device. At the same time, the actual power at a given time can be both higher and lower than the nominal one. When comparing different models of furnaces in terms of heat output, it is important to note that you are comparing the rated power.

What does the rated power of a particular model of wood stove depend on

• the size of the combustion chamber,
• mass and material properties of the furnace (lining of the combustion chamber, body, lining, and so-called “heat storage”),
• effective air exchange (inflow of secondary and tertiary air) into the combustion chamber.

The first factor – the size of the combustion chamber – is quantitative. It determines the amount of wood that can be burned at a time in the boiler chamber. In stoves of the same material and design, the nominal power will be directly proportional to the size of the combustion chamber. At the same time, in order for the actual power of a large stove to be greater than that of a small one, it will be necessary to increase the consumption of firewood (the size of one bookmark of firewood, the size, and the number of logs).

The second and third factors affect the power indirectly, through the efficiency – the coefficient of efficiency, which characterizes the combustion efficiency. Due to high efficiency, you can get more useful heat energy (more power) with the same consumption of firewood. The efficiency of the stove shows the ratio between the potential amount of heat energy contained in the burnt wood fuel and the useful amount of heat energy that can be transferred to heating.

Why is efficiency always less than unity, and where does the difference disappear

Part of the heat is lost with flue gases: the high temperature of the outgoing flue gases indicates an insufficiently efficient process. To reduce heat loss with flue gases in the furnace, a system of one or two deflectors is used – these are transverse plates installed in the upper part of the combustion chamber and prevent the direct flow of gases into the chimney. Thus, the path of the exhaust gases is lengthened, and on the way to the chimney, the gases have time to give off more heat, in addition, part of the flue gases is reflected for secondary combustion (CO is oxidized to CO2 with the release of heat). In addition, in high stoves, part of the chimney runs inside the body, and you can additionally purchase and install a heat storage system – heavy concrete slabs, with a total weight, depending on the model of the stove, from 50 to 600 kg, which surrounds the chimney and accumulates heat from the flue gases and gives it to the room. There are also nozzles on the chimney with radiator plates, which also increase the efficiency of heat extraction, but if installed indoors, they do not look very aesthetically pleasing.