When installing or under a maintenance contract, it is necessary to carry out gas pressure and draft measurements on a boiler to ensure that it operates correctly. A single combustion analyzer or pressure gauge is sufficient to perform these two separate measurements. However, we must respect some precautions that we issue our expert Testo company.
Difference between Gas pressure measurement and Draft measurement
These two parameters measured on a boiler have, in common only the sensor present on the combustion analyzer. It is always a measure of pressure but unrelated in their order of magnitude. A gas pressure of a few tens of mbar (or hPa) is measured at the burner and the Pascal draft in the duct to ensure that the flue gases are evacuated.
There are several gas pressure measurements:
- static gas pressure = gas pressure at the arrival of the boiler stopped,
- dynamic gas pressure = gas pressure at the appearance of the furnace running,
- ramp gas pressure in DHW mode,
- ramp gas pressure in heating mode.
The natural draft is generated by the temperature difference between the combustion products and the ambient air. The draft measurement is only carried out on gas boilers with flue gas type B (non-leakproof) and wood boilers.
Any pressure measurement starts with a zeroing of the sensor. It is, therefore, necessary to know how his measuring device works and to refer to his instructions for use. Regardless of the device used, it must be checked whether, during the zeroing of the pressure sensor, pressurization or not. When measuring gas pressure, make sure that before the zeroing, the hose can be connected between the device and the measurement.
For the draft measurement, it must be checked that the sensor of the device can be in place in the combustion gases during the counting of the zeroing. A draw measurement, some Pascal, is a very low value to which we must take maximum precautions: do not extend the analysis, a few seconds are enough. Position the fixture with magnets to prevent it from moving and interfering with the result. Favor several measures of short duration rather than a means of a long duration. If your device does not perform zeroing automatically, perform a systematic zero before each new measurement. (While respecting the previous warning on the positioning of the probe during the zeroing!)
During the draft measurement, the openings of the room must be closed, the possible hood off, the boiler running, and temperature.
- Static gas pressure: Its value is close to 21 bar. Too low, it highlights a power supply problem.
- Dynamic gas pressure: An excessive loss of pressure indicates a problem on the installation (clogging of a filter, …).
- Maximum boom gas pressure: in DHW mode, will the power be sufficient for the required requirements, too low a pressure will cause a lack of power for the rise in temperature of the DHW.
- Minimum Ramp Gas Pressure: The goal is to achieve the smallest stable flame that can be produced and meet the manufacturer’s specifications. Too little, the flame goes out prematurely, or the boiler does not start.
- Maximum heating ramp gas pressure: the objective is to optimize the power supplied in heating to the existing installation (radiators, floor heating).
- The draft measurement must indicate on a gas boiler a meager value, less than -3 Pa. An amount equal to zero or positive represents a danger of discharge of the combustion gases!
- On wood boilers, the natural draft created is of the order of -10 to -15 Pa. In severe winter conditions, the selection can reach -50 Pa, with very high flue gas temperatures to be measured with a combustion analyzer and overconsumption of wood, causing deterioration of the duct.