The heating boiler is central device heating systems. To operate it at maximum performance and to avoid waste of energy, an accurate calculation of the power of the heating boiler is necessary. A properly designed heat generator will be able to maintain optimal functionality with much lower maintenance costs.
Basic calculation
The power of the heating device requires uniform heat transfer to the network. It is designed to supply heat to buildings of various sizes, be it multi-story building or a country house.
For optimal heating one-story cottage there is no need to purchase an overly powerful boiler, which is designed to heat a 3-4-story building.
The basis for the calculation is the area and dimensions of the building. How to calculate the boiler power taking into account other parameters?
What affects the calculation
The calculation method is specified in building codes and rules II-3-79 (SNiP). In this case, it is necessary to take into account the following characteristics:
- Average territorial temperature in winter;
- the level of thermal insulation of the building and the quality of the materials used for this;
- end location of the room, presence of windows, number of battery sections, thickness of external and interior walls, ceiling height;
- proportional correspondence of the size of openings and supporting structures;
- heating circuit layout form.
For the most accurate calculations, the presence of household equipment (computer, TV, electric oven, etc.) and indoor lighting that can generate heat is often taken into account. But this makes no practical sense.
Information that must be taken into account without fail
Every 10 m² of a private house with average thermal insulation, standard climatic conditions of the region and a typical ceiling height (approximately 2.5-3 m) will require about 1 kW for heating.
More than 20% must be added to the power of the heating boiler, which is designed for joint operation in the heating and water supply system.
Unstable pressure in the boiler and heating main will require equipment with a special device with reserve power, which exceeds the calculated values by approximately 15%.
Force heating boiler, which is connected to the heating system using a coolant (hot water), must also contain a reserve of more than 15%.
The number of possible heat energy losses in poorly insulated rooms
Insufficient quality thermal insulation leads to loss of heat energy in the following amounts:
- Badly insulated walls will transmit up to 35% of heat energy;
- regular ventilation of the room leads to losses of up to 15% of heat (temporary ventilation has practically no effect on losses);
- insufficiently sealed cracks in windows allow up to 10% of thermal energy to pass through;
- an uninsulated roof will draw 25%.
The simplest formula for calculating the required heat energy for heating
For an approximate calculation, there is an elementary formula: W = S × Wsp, where
W is the power of the unit;
S is the size of the building area in m², taking into account all rooms for heating;
Wsp is a standard indicator of specific power, which is used when calculating in a specific climatic region.
The standard power density value is based on experience with a variety of heating systems.
The average statistical information is obtained from a housing and communal services employee in your region. After this, multiply this value by the total area of the building, and you will get average required boiler power.
Calculation example
Gas is the most common type of fuel. How to calculate power gas boiler? Let's consider an example calculation for a building with an area of 150 m², which is presumably located in the Krasnoyarsk Territory. The calculation was made for a heating system with natural circulation without constant pressure from the pump. The specific power in the region under consideration is 0.90 kW/m².
150 m² / 10 m² = 15 is an intermediate calculation coefficient, which implies that 1 kW of the unit’s thermal power is required for an individual 10 m² of heated room area.
15 × 0.90 kW/m² = 13.5 kW.
As a result, the average value of thermal energy required for a specific building with average thermal insulation and climatic indicators was obtained.
If we take into account the use of hot water for the bathroom and kitchen, it will be necessary to add at least 20% to the power: 13.5 + 13.5 × 0.2 = 16.2 kW.
It is worth paying attention to the fact that the pressure in the boiler and the heating main may be unstable; for this it is necessary to add another 15% to the power: 16.2 + 13.5 × 0.15 = 18.225 kW.
Considering that a certain leakage of thermal energy cannot be avoided, it is necessary to round the result up. It turns out that to ensure heating of a specific building using a heating unit on gas fuel you will need a boiler with a minimum power of 19 kW.
Power calculations for gas-fueled units are most often performed during building planning. The reason for this is the original design of the location heating devices, openings for air exchange, chimney, as well as a separate room for a heating installation.
If you need to think about heating in an existing building that does not have necessary conditions To place the unit on gas fuel, you will need to install an alternative heating system. Good for her role electrical installation, the power of which is calculated using similar calculations.
In addition to the above calculations, the thermal power of the boiler can be calculated using a calculator specially created for this purpose. It includes parameters such as the total area of the room, its height, type of windows, etc. To find out thermal power, it is necessary to enter the required indicators into the program, having previously found out their exact meaning.
Calculating the required power to heat a private house is not so difficult task, especially if you use a calculator program. Anyone who wants to save money and provide optimal heating without extra costs thermal energy.
Technical consultants of the Termomir company, who have been working with gas boiler equipment for many years, often hear the question - How to choose a gas boiler based on the size of the house. Let's look at this topic in more detail.
A gas heating boiler is a device that uses fuel combustion (natural or liquefied gas) to heat the coolant.
Design (design) of a gas boiler: burner, heat exchanger, thermally insulated housing, hydraulic unit, as well as safety and control devices. Such gas boilers require a chimney connection to remove combustion products. The chimney can be either ordinary vertical or coaxial (“pipe in pipe”) for boilers with closed camera combustion. Many modern boilers are equipped with built-in pumps for forced water circulation.
The principle of operation of a gas boiler- the coolant, passing through the heat exchanger, heats up and then circulates through the heating system, releasing the resulting thermal energy through radiators, heated floors, heated towel rails, and also by heating water in the boiler indirect heating(if it is connected to a gas boiler).
Heat exchanger - metal container, in which the coolant (water or antifreeze) is heated - can be made of steel, cast iron, copper, etc. The reliability and durability of a gas boiler depend primarily on the quality of the heat exchanger. Cast iron heat exchangers are corrosion resistant and have long term services, but are sensitive to sudden temperature changes and have significant weight. Steel containers can suffer from rust, so their internal surfaces are protected with various anti-corrosion coatings to extend the “life” of the device. Steel heat exchangers are the most common in boiler production. Copper heat exchangers are not susceptible to corrosion due to high coefficient heat transfer, low weight and dimensions, such heat exchangers are often used in wall-mounted boilers, but one of the minuses should be noted that they are more expensive than steel ones.
In addition to the heat exchanger, an important part of gas boilers is the burner, which can be various types: atmospheric or fan, single-stage or two-stage, with smooth modulation, double.
To control a gas boiler, automation is used with various settings and functions (for example, a weather-dependent control system), as well as devices for programming operation and remote control boiler
Main technical characteristics gas heating boilers are: power, number of heating circuits, type of fuel., type of combustion chamber, type of burner, installation method, presence of a pump and expansion tank, automatic boiler control.
To determine required power gas heating boiler for private country house or apartment used simple formula- 1 kW of boiler power for heating 10 m 2 of a well-insulated room with a ceiling height of up to 3 m. If heating of a glazed basement is required winter garden, rooms with non-standard ceilings, etc. The power of the gas boiler must be increased. It is also necessary to increase the power (about 20-50%) when providing a gas boiler and hot water supply (especially if it is necessary to heat the water in the pool).
Feature of calculating power for gas boilers: the nominal gas pressure at which the boiler operates at 100% of the power declared by the manufacturer, for most boilers is from 13 to 20 mbar, and the actual pressure is gas networks in Russia it can be 10 mbar, and sometimes lower. Accordingly, a gas boiler often operates at only 2/3 of its capacity and this must be taken into account when calculating. For more details, see the table for calculating the power of a heating boiler.
Most gas boilers can be convert from natural gas to liquefied gas (cylindered propane). Many models switch to liquefied gas at the factory (when purchasing, check these characteristics of the model), or the gas boiler is additionally supplied with nozzles (nozzles) for switching to bottled gas.
Pros and cons of gas boilers:
Boiler piping- these are devices for full-fledged work heating and water supply systems. It includes: pumps, expansion tanks, filters (if necessary), collectors, return and safety valves, air valves, valves, etc. You will also need to purchase radiators, connecting pipes and valves, thermostats, a boiler, etc. The issue of choosing a boiler is quite serious, so the selection of equipment and its complete set It's better to leave it to professionals.
Which boiler is the best? On Russian market gas boiler equipment has its own leaders in quality and reliability. The best manufacturing companies and brands of gas boilers are presented in an assortment:
"Premium class" or "Lux"- the most reliable and durable, easy to use, the kit is assembled like a “construction set”, more expensive than others. Such manufacturers include German companies
Choice necessary equipment for a heating system is an extremely important task. Owners of private houses are sure to encounter it, and in Lately and many apartment owners strive to achieve complete independence in this matter by creating their own autonomous systems. And one of key points Naturally, there is a question of choosing a boiler.
If the housing is connected to the main natural gas supply, then there is nothing to think about - optimal solution there will be an installation gas equipment. The operation of such a heating system is incomparably more economical than all others - the cost of gas is relatively low, especially in comparison with electricity. All sorts of problems with additional acquisition, transportation and storage of fuel, typical for solid or liquid fuel installations, disappear. If all installation requirements are met and the rules of use are followed, it is completely safe and has high performance indicators. The main thing is to decide correctly the right model, for which you need to know how to choose a gas boiler so that it fully complies with specific operating conditions and meets the wishes of the owners in terms of functionality and ease of use.
Basic parameters for choosing a gas boiler
There are a number of criteria by which you should evaluate the model of boiler you are purchasing. It should be immediately noted that almost all of them are interconnected and even interdependent with each other, so they must be considered immediately and comprehensively:
- The key parameter is the total thermal power of the gas boiler, which must correspond to the tasks specific system heating.
- The location of the future installation of the boiler - this criterion will very often depend on the power mentioned above.
- Boiler type according to layout - wall-mounted or floor-mounted. The choice also directly depends on both the power and the installation location.
- The type of boiler burner - open or closed - will depend on the same criteria. Accordingly, a system for removing combustion products is organized - through a conventional chimney with natural draft or through a forced smoke removal system.
- Number of circuits - will the boiler be used only for heating needs, or will it also take over the provision hot water. If a double-circuit boiler is selected, then its type based on the structure of the heat exchangers is taken into account.
- The degree of dependence of the boiler on the energy supply. This parameter is especially important to take into account in cases where power outages in a populated area occur with alarming regularity.
- Additional equipment of the boiler with the elements necessary for efficient work heating systems, the presence of built-in control systems and ensuring operational safety.
- And finally, the boiler manufacturer, and, of course, the price, which will depend on many of the factors listed above.
The first step is to correctly determine the boiler power
It is simply impossible to move on to choosing any boiler if there is no clarity about what heating installation must be in place.
IN technical documentation boiler, the value of the rated power is necessarily indicated, and in addition, recommendations are often given about how much space it is designed to heat. However, these recommendations can be considered rather conditional, since they do not take into account the “specifics”, that is, the actual operating conditions and features of the house or apartment.
The same caution should be applied to widespread“axiom” that to heat 10 m² of housing area, 1 kW of thermal energy is needed. This value is also very approximate, which can only be valid if certain conditions – average height ceilings, one external wall with one window, etc. In addition, the climate zone, the location of the premises relative to the cardinal points and a number of other important parameters are not taken into account at all.
Thermal engineering calculations according to all the rules can only be carried out by specialists. However, we will take the liberty of offering the reader a methodology self-calculation power, taking into account most factors influencing the efficiency of heating a house. With such a calculation, there will certainly be an error, but within completely acceptable limits.
The method is based on calculating the required thermal power for each room where heating radiators will be installed, followed by summing the values. Well, the following parameters serve as initial data:
- Room area.
- Ceiling height.
- Quantity external walls, the degree of their insulation, location relative to the cardinal points.
- Level of minimum winter temperatures for the region of residence.
- Number, size and type of windows.
- “Neighborhood” of the room vertically - for example, heated rooms, cold attic and so on .
- The presence or absence of doors to the street or to a cold balcony.
Any owner of a house or apartment has a plan for his housing. Having placed it in front of you, it will not be difficult to create a table (in an office application or even just on a piece of paper), which indicates all the heated rooms and their characteristics. For example, as shown below:
| Premises: | Area, ceiling height | External walls (number where facing) | Number, type and size of windows | The presence of a door to the street or balcony | Required thermal power |
|---|---|---|---|---|---|
| TOTAL: | 92.8 m² | 13.54 kW | |||
| 1st floor, insulated floors | |||||
| Hall | 9.9 m², 3 m | alone, West | single, double-glazed window, 110×80 | No | 0.94 kW |
| Kitchen | 10.6 m, 3 m | one, South | one, wooden frame, 130×100 | No | 1.74 kW |
| Living room | 18.8 m², 3 m | three, North, East | four, double-glazed window, 110×80 | No | 2.88 kW |
| Tambour | 4.2 m², 3 m | alone, West | No | one | 0.69 kW |
| Bathroom premises | 6 m², 3 m | one, North | No | No | 0.70 kW |
| 2nd floor, above – cold attic | |||||
| Hall | 5.1 m², 3 m | one, North | No | No | 0.49 kW |
| Bedroom No. 1 | 16.5 m², 3 m | three, South, West | single, double-glazed window, 120×100 | No | 1.74 kW |
| Bedroom No. 2 | 13.2 m², 3 m | two, North, East | No | 1.63 kW | |
| Bedroom No. 3 | 17.5 m², 3 m | two, East, South | two, double-glazed window, 120×100 | one | 2.73 kW |
After the table has been compiled, you can proceed to calculations. For this purpose, below is posted convenient calculator, which will help you quickly determine the required heating power for each room.
The level of negative street temperatures is taken from the average characteristic of the coldest ten-day period of winter in the region of residence.
Autonomous heating for a private home is convenient, affordable and very diverse. Any owner of a private home willingly buys a gas boiler and installs everything necessary so that he no longer depends on the vagaries of the weather or surprises related to work centralized systems heating.
However, it is important to choose the right equipment. If its power exceeds the actual heat needs of the building, part of the heating costs will simply be thrown away. A device with low performance will not be able to provide the house with enough heat. Therefore, even at the design stage, you need to find an answer to the question: how to calculate the power of a gas boiler?
What quantities are used in the calculations?
The simplest calculation of boiler power by area looks like this: you need to take 1 kW of power for every 10 sq. m. However, it is worth considering that these standards were drawn up during the Soviet Union. They do not take into account modern construction technologies, in addition, may turn out to be untenable in areas whose climate differs markedly from the conditions of Moscow and the Moscow region. Such calculations may be suitable for a small building with an insulated attic, low ceilings, excellent thermal insulation, double-glazed windows, etc. Unfortunately, only a few buildings meet these requirements. To make a more detailed calculation of the boiler power, you need to take into account a number of factors, such as:
- climatic conditions in the region;
- dimensions of the living space;
- degree of insulation of the house;
- possible heat loss of the building;
- the amount of heat required to heat water.
Moreover, in houses with forced ventilation The calculation of a heating boiler must take into account the amount of energy required to heat the air. As a rule, you need to use special software for calculations:
When calculating the power of a gas boiler, you should add about 20% more in case of unforeseen situations, such as severe cold or a decrease in gas pressure in the system.
Is it worth buying a boiler that is too powerful?
Modern heating equipment is equipped automatic systems, which allow you to regulate gas flow. This is very convenient because it eliminates unnecessary expenses. It may seem that an accurate calculation of the power of a heating boiler is not so important, because you can simply buy a boiler with high power ratings. But it's not that simple.
Correct selection of heating equipment will extend its service life
Unreasonably exceeding the thermal power of equipment can lead to:
- increasing costs for the acquisition of system elements;
- reducing the efficiency of the boiler;
- failures in the operation of automatic equipment;
- rapid wear of components;
- formation of condensation in the chimney, etc.
Thus, you need to try to “get into” exactly the power that suits your home.
Gas boiler for standard houses
- MK is the design power of the boiler in kW;
- S – total area premises in sq.m;
- UMC is the specific power of the boiler, which should be for every 10 sq. m.
The last indicator is set depending on the climate zone and is:
- 0.7-0.9 kW for southern regions;
- 1.0-1.2 kW for the middle band;
- 1.2-1.5 kW for regions near Moscow;
- 1.5-2.0 for northern regions.
According to this formula, the estimated boiler power for a house with an area of 200 square meters. m., which is located in middle lane, will be: 200X1.1/10=22 kW. Please note that this formula shows how to calculate the power of a boiler that is used only for heating a house. If you intend to use a double-circuit system that provides heating of water for domestic needs, the power of the equipment should be increased by another 25%.
How to take ceiling heights into account when calculating?
Since many private houses are being built according to individual projects, the methods for calculating boiler power given above will not work. To make a fairly accurate calculation of a gas heating boiler, you must use the formula: MK = Qt*Kzap, Where:
- MK – design power of the boiler, kW;
- Qt – predicted heat loss of the building, kW;
- Kzap is a safety factor that is 1.15 to 1.2, i.e. 15-20%, by which experts recommend increasing the design power of the boiler.
The main indicator in this formula is the predicted heat loss of the building. To find out their value, you need to use another formula: Qt = V*Pt*k/860, Where:
- V - volume of the room, cubic meters;
- Рt - difference between external and internal temperatures in degrees Celsius;
- k is the dissipation coefficient, which depends on the thermal insulation of the building.
The dissipation coefficient varies depending on the type of building:
- For buildings without thermal insulation, which are simple designs made of wood or corrugated iron, dissipation coefficient is 3.0-4.0.
- For structures with low thermal insulation, typical for buildings with single brick laying with ordinary windows and roof, the dispersion coefficient is taken to be 2.0-2.9.
- For houses with an average level of thermal insulation, for example buildings with double brickwork, a standard roof and a small number of windows take a dispersion coefficient of 1.0-1.9.
- For buildings with increased thermal insulation, well-insulated floors, roofs, walls and windows with double glazing use a dispersion coefficient in the range of 0.6-0.9.
For small buildings with good thermal insulation, the design power of heating equipment can be quite small. It may happen that there is simply no suitable gas boiler on the market with the required characteristics. In this case, you should purchase equipment whose power will be slightly higher than the calculated one. Systems automatic regulation heating will help smooth out the difference.
Some manufacturers have taken care of the convenience of customers and have placed special services on their Internet resources that make it possible to calculate the required boiler power without any problems. To do this, you need to enter the following data into the calculator program:
- temperature that must be maintained in the room;
- average temperature for the coldest week of the year;
- need for hot water supply;
- presence or absence of forced ventilation;
- number of floors in the house;
- ceiling height;
- information about floors;
- information about the thickness of external walls and the materials from which they are made;
- information about the length of each wall;
- information about the number of windows;
- description of the type of windows: number of cameras, glass thickness, etc.;
- dimensions of each window.
Once all the fields are filled in, you can find out the estimated power of the boiler. Options detailed calculations boiler power various types are clearly presented in the table:
This table has already calculated some options, you can use them as the correct ones in advance (click on the picture to enlarge)
Our calculator for quick calculations
To calculate the thermal power of a heating boiler in this calculator, just enter the area of the heated room, select the necessary parameters and click the “Run calculation” button.
How not to make a mistake and choose the device wisely so as not to freeze and not stretch your budget - read on. From the article you will learn which technique will be correct and necessary for you.
Calculation of heat losses at home
Let us say right away that there is no single method for calculating the coefficient. The setting varies depending on your climate. It is all the more important to pay more attention to this stage of preparation. Even a specialist cannot determine by eye, without calculations, information on required power boiler Even low-power ones, like , can heat an average apartment up to 65 m². But what exactly it should be will become known after filling out a special questionnaire - the document is freely available, anyone can fill it out on the Internet.
The experts took a responsible approach to compiling the questionnaire. By filling out the fields, you will not be able to make a mistake. The only exception is incorrect completion of the online form. All other boiler calculations for the house will be made by the program.
So, here are the questions you need to be prepared for - check:
1. Heat loss through walls
This parameter is influenced by the area of the façade and the ventilated layer (walls may or may not have it). The first covering of the walls is the primary criterion, without which choosing a heating boiler will be too risky. Reinforced concrete or foam concrete, mineral wool, plasterboard, plywood or wood - the material influences the decision of what power to buy solid fuel equipment. The thickness of the first layer of the house is also important. For thin-walled houses, buy a medium-power boiler - for example.
2. Heat loss through windows
Important condition. It is logical that more heat will be lost with a single-chamber double-glazed window than with double-chamber ones. The area of the windows is also important when calculating the power of the boiler. Measure it again before filling out the questionnaire.
3. Heat loss through the ceiling and floor
As you understand, in a room with an attic and an unheated basement you need to install powerful equipment - like. Incorrectly selected power of the device will ruin several winter months held in country house- heating is clearly not enough for a comfortable life.
Useful for information:
If you do everything correctly, your efforts will be rewarded with a profitable investment in your purchase. Consider that you have completed the task - most likely you will receive best result in terms of price and quality.
Why is it important to accurately determine the boiler power?
The first thing that comes to mind is saving money on purchases. This alone is worth spending a couple of hours on calculations. Considering Good work And efficient operation boiler - calculating the power of the equipment becomes even more necessary.
Here are some sad scenarios that will inevitably unfold if the above is not taken into account.
Remember: The regional adjustment for our climate is a factor of 1.2.
Incorrect calculation of the power of a less popular, but still available pellet device (for example) and a wood-burning boiler is the first choice parameter. To calculate the parameter, do not be lazy to spend time, otherwise you cannot avoid the above problems in lack of heat (if we are talking about weak appliances) or irrational excessive consumption of fuel (when you select an expensive and too powerful boiler, like).
Determining the boiler power is the most important stage of work
So you have become familiar with the theoretical part of the question, having received information about the importance of calculating the power of boilers. Now it's time to move on to the practical part - the most important. As an option, a specialist responsible for calculating parameters and installation. But you yourself can find out what equipment is really needed.
When calculating power, we start from the area of the heated object - it is this that will help assess productivity. Keep in mind that with a room height of 2.7 m (and such ceilings in almost all houses), it takes 1 kW to heat 10 m².
This coefficient is approximate. It is influenced by the climate of the region and, again, the height of the ceilings, the presence basements etc.
Advice: to calculate the power of an ideal boiler for high ceilings, it is necessary to identify a correction factor by dividing the parameter by the standard 2.7 m.
Example:
- The ceilings are 3.1m.
- Divide the parameter by 2.7 - we get 1.14.
- Yes, for high-quality heating a house of 200 m² with ceilings of 3.1 m will need a boiler with a capacity of 200 kW * 1.14 = 22.8 kW.
- To ensure you don’t freeze, we recommend rounding the parameter up. Then you get 23kW. 24 kW will suit us.
Please note that this calculation is suitable for a single-circuit boiler. In the case of, you need to calculate what temperature of water you want to get in the cold, and choose equipment in accordance with the parameter (+25%, power, if you like your water hotter).
Step-by-step calculation of boiler power (double-circuit) for apartments
With apartments the situation is somewhat different. Here the coefficient is less than in a house - in apartments there is no heat loss through the roof (unless we are talking about top floor) and losses through the floor (except for the first floor).
- if the apartment above is “warmed” by another room, the coefficient will be 0.7
- if there is an attic above you - 1
To calculate the parameter, we use the method indicated above, taking into account the coefficient.
Example: The area of the apartment is 163 m². Its ceilings are 2.9 m, the apartment is located in our strip.
We determine the power in five steps:
- We divide the area by the coefficient: 163m²/10m²= 16.3 kW.
- Do not forget about the adjustment for the region: 16.3 kW * 1.2 = 19.56 kW.
- Since a double-circuit boiler is designed for hot water, add 25% 7.56 kW*1.25=9.45 kW.
- And now don’t forget about the cold (experts advise adding another 10%): 9.45 kW * 1.1 = 24.45 kW.
- We round it up and it comes out to 25 kW. It turns out that a device that runs on natural gas and interacts with solar collectors will suit us.
Please note that in this way the power of boilers is calculated, no matter what fuel they operate on - be it gas, or electricity, or solid fuel. .
Step-by-step calculation of boiler power (single-circuit) for an apartment
But what if you don’t need a double-circuit boiler, and with tasks? Let's make calculations, taking into account one more factor - the material the house is made of. The heating standard established at the legislative level looks like this:
- Heating 1m³ in panel house will require 41 W.
- Heating 1m³ in brick house will require 34 W.
We invite you to familiarize yourself with:
We remember the area of the apartment, multiply it by the height of the ceilings, and get the volume. This indicator must be multiplied by the norm - we get the boiler power.
Example:
- You live in an apartment with an area of 120 m², and its ceilings are 2.6 m.
- The volume will be: 120m²*2.6m=192.4m³
- We multiply by the coefficient and calculate the heat requirement 192.4 m³ * 34 W = 106081 W.
- Converting to kilowatts and rounding, we get 11 kW. This is the power a single-circuit thermal unit should have. A good option is the model. A little "with reserve", the power of this equipment is more than enough for a comfortable microclimate in your home.
As you can see, the task of selecting a boiler will not take more than an hour. By choosing the right heating device, you will be protected from uncomfortable cold throughout the winter, saving money on the purchase of a boiler, public utilities. Correctly calculating the parameter is equally important for all types of heaters: coal, TT,