Hydraulic balancing of a heating system means controlling the flow of the heating medium (hot water) through the system peripherals (pipes, radiators), aiming at optimal distribution of heat generated in a boiler to individual rooms in amounts desired by the user. The water transport route (pipes) must be adequate to the needs, must have adequate flow rate.
An element regulating the flow of the heating medium (water) in the heating system is the suitable graduation of pipe diameters (e.g. DN 22-18-15), which ensures its adequate distribution to individual circuits and branches. Another commonly used method of hydraulic balancing of a system are presets, shut-off valves, and more recently rotameters (flow meters).
The diameters of pipes, the same as on the supply lines to radiators, are used on the return lines to the boiler.
From each radiator, we can “squeeze out” more power by speeding up the flow of water (e.g. more efficient circulation pump or pump working at a higher gear), but this may be accompanied by clearly heard sound of flowing water.
We can accept the general principle that high power radiators, i.e. above 2700 W, must be necessarily supplied using connecting pipes with a diameter of ¾”.
Smaller heaters can be powered with connecting branches with a diameter of ½”.
The condition for good, high-efficiency, no-noise operation of the system, as well as the condition for a long period of its service life, is its careful construction, consistent with good installation practice. After selecting the material of which the system will be built, carefully check the rated power (size) of radiator to choose the right diameter of connecting pipes. Appropriately selected diameter will guarantee an adequate flow. The internal diameter of the connecting pipes is dependent on the material from which the system is made (copper or plastic) and the size (rated power) of the radiator. A system made of copper has a much thinner walls than pex-al-pex or polypropylene pipes. Hence, the inner diameter of the copper pipes is larger than the inner diameter of polypropylene or pex-al-pex pipes, because with more powerful radiators (grey area in the chart), you can still use the 1/2 inch copper pipes, but plastic pipes should be 3/4 inch.
Chart showing the relationship between the minimum diameter of the connection and the rated power (size) of a trench radiator with a fan (W)