What is the best heat exchanger for the solid fuel boiler

Solid fuel boiler protection

There are many different devices for the protection of the boiler, but it is worth remembering that the same valve / pump / sensor, manufactured in China and Germany have a completely different life span and degree of reliability!

Solid fuel boiler safety group

Safety group for solid fuel boilers consists of an automatic air vent, pressure gauge and safety relief valve on the common manifold.

The air vent removes air that is in the heating system. The first portions of steam produced in the boiler drum during overheating are discharged via the pump.

Manometer allows visual control of pressure in the tank and the entire heating system.

Safety valve is triggered in case of emergency. Discharges water and steam if their pressure exceeds the permissible value.

In fact, it turns out that immediately the pressure gauge registers the increase in pressure, then the resulting steam is discharged through the air vent. And lastly the water and steam are discharged by the safety valve. All of this combined will protect your solid fuel boiler from overheating.

Uninterruptible power supply (UPS)

UPS is an inverting device converting low voltage (12-24 V) from the battery to 220 V needed by the circulation pump and the automatics.

Depending on the load and the model of the device uninterruptible power supply can run (and ensure the operation of electronic components of the heating system) from a few hours to several days.

The main condition for the proper functioning of the heating system with an uninterruptible power supply is the correct choice of the latter. It is necessary to take into account what tasks and under what conditions the device will perform.

It is better to choose a more powerful UPS with capacitive battery. It is more expensive, but it provides operation of the equipment for many hours.

Buffer tank (heat accumulator)

It is a steel, often insulated tank of large volume (from several hundred to several thousand liters). Mounted between the boiler and the heating circuit. The heating medium does not flow directly into the heating pipes but via an accumulating tank. There, the hot water mixes with the cooler water and only then enters the radiators.

At switching-off of a power it provides continuous cooling of the heat-carrier, allows to avoid overheating of the boiler and when all fuel burns out some more time supports a comfortable temperature in the house.

By the way, in some European countries it is prohibited in principle to operate a solid fuel boiler without a buffer tank.

Two way safety valve or overheating protection valve

not to be confused with a safety valve.

The device is not dependent on mains electricity. Connects to the supply and return lines, water supply and sewerage. When reaching a critical temperature of the coolant (above 95C) mixes the incoming hot water from the boiler with cold tap water and feeds it into the boiler via the return pipe. Excess hot water is discharged into the drainage system.

Emergency circuit in the boiler system

Let us make it clear right away: an emergency circuit can be implemented in various ways and with various components. For the final result is responsible installer, who proposed or approved the final variant.

We, for example, consider this option of an emergency circuit: part of the system will use the forced type of circulation, and part of the gravitational. Then when the electricity (and with it the circulation pump) is switched off, the forced circulation is stopped. Only a small heating circuit with gravity circulation works. Thus only part of the building is heated, but the boiler does not overheat.

By the way it can be quite difficult and expensive to organize such a scheme of work in the existing system. But when designing heating from scratch, it is much easier and cheaper to consider this (or any other) option.

Built-in emergency heat exchanger

Mounted in such a way that in the event of an accident, cold water from the water supply is passed through it. This allows for some cooling of the overheated heating unit, if necessary. A method not very common and not superefficient, because the heat exchanger is usually a small area and can only slightly reduce the temperature. In addition, this method of protection can be implemented only if the house is connected to the water supply. Most often found in homemade boilers.

What are cast iron solid fuel boilers

The main distinguishing feature of cast iron models is the resistance of cast iron to corrosion. Steel heat exchangers have not so thick walls, the lifetime of which is simply limited by the physical properties of the metal. Already after 12-15 years the metal is destroyed and the heat exchanger leaks. The situation can be insignificantly improved only by using purified and softened coolant.

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Cast iron heat exchangers have thicker walls, and the metal is not subject to corrosion, after many years it can only be slightly covered with a rusty crust on the outside. Therefore, their service life when using any heat transfer medium is more than 30 years.

Only light rust inside the sections of the cast iron heat exchanger after more than 7 years of operation.

However, there are many known disadvantages: first of all. brittleness. Cast iron boiler units should be transported and installed with extreme care, even minor mechanical damage can cause cracking or destruction of sections. The situation is aggravated by huge weight of such models. 150-220 kg on average, versions with power of 40 kW and more can weigh more than 300 and even 400 kg.

The cast iron heat exchanger consists of permanently connected sections. Boiler output depends on the number of sections. Unlike the solid steel one, a damaged cast iron heat exchanger section can be easily replaced.

Also the fragility is manifested in the sensitivity to sharp temperature differences, for example, a large difference between the supply and return lines. In addition to careful monitoring of temperature differences, the problem can be solved by installing a four-way mixing valve, through which the return line is mixed a certain amount of heated coolant from the supply. To compensate for the above disadvantages, some leading manufacturers produce the heat exchanger from more advanced alloys, such as gray cast iron alloys. However, the cost of such models is 20-50% higher.

The advantage and at the same time disadvantage of cast iron heat exchangers is their high inertness. Cast iron takes longer to heat up, but it also takes significantly longer to give the heat energy to the heat carrier. However, it is impossible to adjust the work of the boiler or quickly change the desired temperature level.

Cast iron solid fuel boilers can burn wood, coal, wood briquettes, pellets, then. Almost all models are able to work on any of the kinds, but there are also models whose design involves working only on firewood.

There are both single-circuit, designed only for heating, and two-circuit models, designed for heating and hot water supply at home. Power household cast iron boilers range from 8-120 kW.

Solid Fuel Boiler Heat Exchanger

Boiler units of long combustion

Separately, it is worth allocating long-playing models in which the duration of burning of one load is 2-5 days. Achieve this result by increasing the volume of the furnace and a more economical principle of combustion from top to bottom.

Often, cast iron solid-fuel boilers for long combustion are more technologically advanced, can be equipped with advanced automation. Despite the cast iron heat exchanger, the body is often made of steel, which reduces the weight and cost of the boiler. However, such models still cost 1.5-2 times more expensive.

  • Nuances and non-obvious points when choosing a boiler;
  • What types of solid fuel boilers there are;
  • Wood-fired boilers (they are also boilers of continuous combustion) are a budget option;
  • Boilers long combustion differences and varieties (conventional, candles and miners);
  • Mine type boilers underestimated model;
  • Pyrolytic boilers myth or reality?;
  • Pellet boilers are an expensive solution to all problems;
  • Installation of a solid fuel boiler is also an expense;
  • How to choose the right solid fuel boiler.
  • Power. Here the buyer should pay attention to the technical characteristics of the liked model. Manufacturers specify the maximum power, temperature, the estimated area.
  • Principle of operation. The main nuance of the number of circuits. Units with one circuit only produce heat in the room, and with two additional provide a person with hot water for household needs.
  • Opportunities. The devices are equipped with various systems to control the combustion process and fix the desired temperature. Some modern models are equipped with hobs, on which you can cook food.
  • Type of fuel and cost. Here a person is better to start from personal preferences and financial capabilities. Fuel in the form of coal, wood raw material is considered economical.

Before we consider our rating of the best solid fuel boilers 2021, we would like to answer a number of important questions that will help determine the purchase for many first-time users. First, you need to decide what to choose: a single-circuit boiler with a boiler or a column, or a two-circuit analog, equipped with an additional heat exchanger for the organization of hot water supply. Due to the fact that our list contains an overwhelming number of affordable and mid-budget models, we focused on single-circuit solutions (mainly) for several reasons: they are cheaper; in case of breakdown, the whole house will not be left without heat; boiler and boiler provide for quick access to heat and DHW. On the other hand, two-circuit models provide space savings, because they combine two types of equipment.

In turn, according to the principle of operation, all solid fuel solutions for the home can be divided into several categories:

  • Pyrolysis. in such equipment, the fuel smolders, not burns, as in the case of counterparts, resulting in the emission of only gases, which, in turn, are saturated with heat. It is important that the wood and processed products have high humidity for pyrolysis;
  • Classic. in such systems, the heat is released by the flaming combustion of solid materials, and to maintain the temperature you have to regularly update the supply of coal, wood and waste recycling, including stumps;
  • Prolonged combustion. in such devices, heat is produced slowly, which is due to the name of the equipment. The main advantage is the burning time of wood, up to several days.
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The original system of solid fuel boiler of this type has a two-chamber design. In the first chamber, when there is a lack of air, the fuel burns, releasing pyrolysis gas. In the second chamber burns pyrolysis gas, this process can be regulated, which allows you to save fuel. Two-stage combustion allows the solid fuel to burn completely, this increases efficiency. The equipment is more comfortable to operate, but requires the use of dry wood and depends on electricity. ChoiceExpert Team.Ru analyzed 9 models and chose 3 pyrolysis boilers that are highly efficient, reliable and do not require complex maintenance.

Vesuvius Elbrus-10

Simple and reliable design, designed for heating a small house or cottage, up to 100 square meters in area.м. Runs on wood and coal, the installation of the heating element of 6 kW power is provided. Recommended system pressure up to 3 atmospheres. The design of the heat exchanger facilitates access for cleaning. Efficiency reaches 80%, approaching the indicators of boilers for diesel fuel.

Body made of structural steel, sealed doors made of cast iron. Thermostat, heating element and heating system can be connected to either side of the body. The equipment is designed to work in systems with natural and forced circulation.

  • Precise adjustment of the power helps to create a comfortable microclimate;
  • Efficient basalt thermal insulation;
  • Compact design;
  • On one charge of firewood burns for 8 hours;
  • Easy maintenance.

Model features a simple design that makes it possible to dispense with the installation of a chimney operating on electricity. Energy-independent pyrolysis boiler. an economical solution for country houses and cottages in a remote from civilization settlement.

Burzhuy-K Standard-20

High power and efficiency of 85% allow you to use equipment for the heating system of the house area of 200-220 square meters.м. The heat exchanger is made of heat-resistant steel. Voluminous chamber allows the use of wood, up to 55 cm in length. Works on all types of solid fuels. The maximum temperature of the coolant. 95 degrees, the pressure in the system can reach 4.5 atmospheres.

The model is equipped with a thermostat and a flue pipe with flap. Mechanical control makes the system energy-independent. Built-in thermometer and manometer make it easy to control key operating parameters.

  • Burning time on a single load of wood for up to 12 hours;
  • Low percentage of harmful emissions into the atmosphere;
  • The maximum rancor fuel;
  • High speed room heating;
  • Manufacturer’s warranty 30 months.

Atmos DC 32 S

Powerful model designed for heating buildings with the area of 250-350 square meters.м. Creation using heat-resistant steel, thickness from 3 to 8 mm. Ceramic blocks are used to increase heat transfer in the chamber. Power automatically adjusted by an electromechanical damper. Regulator acts as overheat protector. Regulating thermostat controls fan that blows air and maintains set temperature. Can work when the fan is switched off, the power is reduced by up to 70%.

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The model can be equipped with a proprietary electronic regulation system that takes into account indoor and outdoor temperatures. Microcontroller controls fans and other equipment to save fuel and increase combustion time on a single charge.

  • Up to 90% efficiency;
  • Roomy chamber;
  • Maximum length of billets 53 cm;
  • Dustless ash collection;
  • Cooling circuit protects against overheating;
  • Automatic shutdown after fuel burnout.

All modern boilers (even the simplest), in addition to innovative principles of operation, have some design features that increase their efficiency and simplify maintenance.

  • Developed heat exchanger each manufacturer calls it differently, some have it “water shelves”, at some “convection channels”, and also “deployed heat exchanger” and t.д. aka water, aka water cooled. (a.k.a. movable rusht;).

Water shelves (aka convection ducts)

These are horizontal, vertical or angled branches of the water jacket (see picture on left). photo). Contribute to improving boiler efficiency by increasing the heat exchange surface.

But their main purpose is to remove heat from the outgoing flue gases. Different manufacturers may have two-, three- or four-pass systems., and the final temperature of flue gases is 120-180 degrees (depending on the number of shelves), which increases the boiler efficiency and significantly reduces the consumption of firewood or coal. For comparison, in a conventional boiler without convection channels the flue gas temperature averages 350-400 degrees. The difference between these rates flies down the chimney instead of going to heating the house.

Water shelves can be found in medium-priced boilers, as well as in all premium boilers.

And a simpler system of fire tube (the principle is the same, but the area is several times smaller) is used even in inexpensive solid fuel boilers. As a result, we have such interesting models such as Beacon AOT, Bizon Economy and Altep Mini.

Water cooled grates

They differ from conventional ones in the fact that they are made of high-temperature solid drawn pipes and are filled with water (coolant) from the inside. That is welded into the heat exchanger of the boiler.

  • Increases the service life of grates, because they are cooled and, therefore, suffer less from thermal shocks.
  • Allows using the grates as an extension of the heat exchanger. That is, the heat from the bottom of the furnace is used to heat. Can be found in boilers of all price ranges.
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Unfortunately, on the Internet you can find conflicting opinions about the durability of such grates, although all these disputes are easily broken by arguments from the textbook on physics in the 7th grade: as long as there is water inside the heating system (and therefore inside the boiler) no burning of grates is impossible in principle!

Nozzles (point air supply)

Modern solid fuel boilers of premium class are produced with 2-4 rows of nozzles, which look like holes in the furnace, through which the air blown by a fan enters.

This solution enables fast melting of the boiler, more efficient burning of any fuel, the possibility of tuning the upper combustion, afterburning the unburned fuel (even of high humidity) and of course extending the burning time on one fuel charge.

By the way, some models of boilers (e.g. Altep Duo Plus series and TOPTERMO series LCD) are made with air knobs on the side walls, with which you can open/close the desired row of jets. Sounds complicated, but in fact it is easy to learn and useful to have such tools to control the boiler.

A lever for shaking off the grate

Allows avoiding the reduction of the boiler output, as well as its fading due to soot and slag clogging of grates.

Those who have already used poor quality (especially high moisture) wood or coal know how much fuel trivially does not burn to the end and gets piled up.

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For shaking the fuel in the grate area, there is no need to perform complex manipulations and apply a lot of effort. It is enough to turn the lever a few times, which breaks up the caked fuel.

A caveat here: this lever is only needed for burning coal, and since it is now a problem, it is not often seen in a modern solid fuel boiler.

Currently used in Marten Comfort series, MaxiTerm Profi and Polish Kamen boilers WG STANDARD and DREMAX series.


To heat as before, regulating the air flow manually it is even impossible to imagine. Modern solid fuel boilers, even the cheapest ones, are easily equipped with automatics, which include:

  • Mechanical draught regulator (a chain on the thermostat head that raises or lowers the air damper itself). Used in medium and budget class boilers.
  • Automatics for solid fuel boilers: control unit and blower. Many variants, on any capacity, quantity of pumps, with measurement of temperature of flue gases, with management of a water heater, an underflow of water in warm floors, etc.д. Used in medium and premium class boilers.
  • Room regulators. The meaning of the same as above, but connected separately and measures the temperature is not coolant in the heating system, but directly in the room which you want to heat.

And what to do without remote access in the modern world? With the help of such automatic control the boiler on solid fuel can be operated via Wi-Fi or by SMS.

You can read more about this in our article: “Automation of solid fuel boilers”.

How to choose and what to pay attention to?

The most important indicators when choosing solid fuel boilers for long combustion with a built-in water loop are:

  • Availability of the necessary fuel.
  • The power level of the device depends on the area of heated premises and the required temperature mode of the coolant.
  • Type of draught created inside the furnace chamber. Can be forced or natural. This parameter affects the possibility of installation in a particular room and the output level of the boiler.
  • Efficiency factor. It will depend on the type of fuel used, the specific construction and the additional equipment used (extraction, automation of fuel supply, etc.).п.).
  • The material of the heat exchanger, usually cast iron or steel, affects the reliability of the unit and the thermal engineering characteristics.
  • The type of location of the water jacket is important for determining the right location to install the boiler in terms of fire safety regulations.
  • The weight of the unit is an important factor in determining the base where the boiler will be located. It must be strong enough and not subject to distortion.
  • The method of fuel loading and dimensions of the combustion chamber are important in determining the cycle of use of the unit and the possibility of setting up automated maintenance.
  • The design features of the ash pan and its accessibility will affect the ease of maintenance and preventive maintenance of the boiler.
  • Costs depend on a combination of the factors listed above and the reputation of the equipment manufacturer.

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