Air in the heating system of a private house

Recommendation points

• Where does air come from and what are the consequences
• Determination of the location of the accumulation of gases
• The problem of counterclones
• Automatic bleed valves
• Bleeding air from radiators
• How to prevent traffic jams

Even small air pockets can disrupt the operation of the hydraulic heating system of a private house. Removing air is a fairly simple task, however, it requires a responsible approach. In particular, it is important to know the causes of air congestion before proceeding with their elimination..

Where does air come from and what are the consequences

Heating systems only at first glance seem to be closed circuits that are filled to capacity with water. There are a number of ways in which air can enter, with clear negative consequences..

To understand how an air lock affects the operation of the heating system, consider the most common pipe in cross section. If it is completely filled with coolant, then its flow rate in this area will be equal to the calculated one, which means that everything will work as provided by the project. However, when air appears in the system, the picture changes dramatically: gases are lighter than water and accumulate in the upper part, thus, the nominal passage of the pipes is reduced. The latter leads to a decrease in the flow rate, due to which the heating devices located in the direction of movement of the coolant do not receive enough heat.

The main source of air in a closed hydraulic system is threaded and sealing connections, which for some reason have lost their tightness. Leaks in these places are scanty, but such defects pose a great danger: since the entire circuit is sealed, then not only water flows out through the fistula, but also a small portion of air is sucked in. Visually, it is difficult to determine the location of such leaks: the water is released in small portions and evaporates almost immediately, but the air entering the inside gradually accumulates. Despite the fact that the nominal pipe passage in modern heating systems is quite small, a plug can form in just a few days.

Another source of gassing is the coolant itself. In systems with automatic make-up, the water is periodically replaced by fresh water saturated with nitrogen and oxygen. These gases are released by bubbles when heated and vigorously stirred. If aluminum radiators are used as heating devices, hydrogen may be released during the reaction of internal surfaces with water. The intensity of the reaction increases in the presence of abrasives in the water, stripping off the protective hydroxide film, as well as in the case of a strong deviation of PH from neutral.

Finally, air in the heating system can appear during a full or partial refueling of the system during repair work. So, when the radiators, circulation pump or other fittings are installed back, there is a certain amount of air inside the devices, which inevitably enters the system. Underfloor heating pipes can serve as another source of gases: due to their considerable length and small wall thickness, they can entrain oxygen contained in the environment.

Determination of the location of the accumulation of gases

To eliminate an air pocket, you must first determine the place of its formation. In total, two sections of the system can be distinguished in which air locks can form – these are horizontally directed pipelines and radiators..

In a properly designed and installed heating system, radiators can be the only place where air can collect. The formation of traffic jams in them is accompanied by the appearance of noise – the murmur of flowing water. Another evidence is the absence of a correct gradient of temperature drop from the upper zone to the lower: since air has accumulated at the top, the water does not contact the walls and does not heat them, but the lower part is quite hot.

It is more difficult to determine if air is in pipes. Since there are no eddies in the straight section, the formation of a plug is not accompanied by extraneous noise. The only way to establish the presence of air is to note a decrease in the flow rate of the coolant. In other words, insufficient heating of the radiators located in the direction of movement of the coolant after the problem area will serve as confirmation. In this case, the overlap of the radiators located before the plug will not lead to an increase in the flow rate and an increase in the temperature of the remaining heating devices.

The problem of counterclones

A typical mistake in the installation of heating pipelines is the formation of a kind of hump in a local area. It is quite obvious that when the system is filled with water, a plug will form in the rising part of the pipe, which cannot be removed from there. Even in open heating systems, where there is a free exit for the air that has entered the circuit, these places are always completely or partially blocked..

In the classical configuration of heating pipelines, the mains always have a slope towards the movement of the coolant, which helps to reduce the total hydrodynamic resistance of the pipes. Therefore, the best way to get rid of counter-slopes is to examine the entire structure and establish the places where this rule is violated, and then re-install the pipes in accordance with the requirements.

However, it is not always possible to do this: openings can interfere with changing the position of the pipes, and such work is almost always associated with the risk of damage to the finishing coatings. The only way to get rid of the air in these areas is with a wet tie-in of the vertical branch. This is done like this: a patch clamp with a ball valve packed on its outlet is mounted on the pipe. When the tap is open, a hole is drilled in the pipe, then the tool is removed from the pipe and the tap closes immediately.

Automatic bleed valves

In systems with an upper position of the supply line, there is a common high point to which all the air generated in any part of the system is directed. Installing an automatic valve in this place will help to solve the problem of air congestion once and for all..

You need to understand that such valves operate under excess pressure and therefore there is a sense in installing them only for closed heating systems, while in open ones, the expansion tank does an excellent job with this function. Also, a prerequisite for installing a bleed valve is the correct organization of the slope of the pipeline: if there is a counter slope in any place on the supply or return pipeline, the air simply will not reach the point where it is automatically removed.

The bleed valves hide a rather delicate and delicate mechanism inside. Their installation should be carried out on a vertical branch from the highest point, about 10-15 cm long. A mud filter must be installed in front of the bleed valve to prevent small debris from entering the mechanism. There may be several automatic venting devices, for example, in systems with beam wiring, they are installed on each collector, that is, at several highest points of the system..

Bleeding air from radiators

To eliminate air locks in the radiators, special fittings should be provided. Mayevsky’s manual taps for air bleeding are installed in one of the upper radiator outlets. If both taps are used to connect pipes, a bleed valve is installed in the branch through a tee pointing vertically upwards. In this case, the valve must be installed in the direction of the flow after the radiator.

To bleed air, it is necessary to increase the circulation of the coolant, bringing the pump to the maximum performance mode. After that, the valve is slightly opened for 1–2 turns, the characteristic hiss indicates the release of air. After the air flow dries up, another 100-150 ml of water is drained from the system and the tap is closed back.

In some cases, it happens that one air lock interferes with the exit of the other. In this case, the radiator heats up normally for some time, but over time, the flow rate of the coolant in it is again limited by the newly formed plug. The treatment is simple: repeat the bleeding operation at intervals of several hours until a direct flow of liquid without bubbles begins to flow from the tap.

How to prevent traffic jams

Air can also enter the system in full or partial charging mode. If the coolant has been completely drained from the system, it must be refilled with a minimum head. At the same time, it is recommended to wait until the water level in the system covers the radiators and turn on the circulation pump several times for 5-10 seconds, providing limited movement of the coolant, due to which small air pockets accumulating at the top of the pipes on flat areas are eliminated. In closed heating systems at the highest point, a valve must be provided for the outlet of air, which is replaced by water..

If any element of the system: a pump, a radiator or a hydraulic arrow, was temporarily dismantled without completely draining the coolant, it is necessary to re-install them with local filling. In this case, one of the upper connection pipes is not immediately sealed, instead, the tap opens at the lower connection point, the internal volume of the device is filled with water, and most of the air comes out of the upper leaky connection.