34
EN
cod. 3545453/0 - 06/2019
PREXTHERM RSW N
fig. 7
fig. 8
5.4 Discharge of combustion products (Fig. 8)
The flue and flue stack fitting must be made in accordance with current standards and legislation, using rigid pipes that are resistant to high
temperatures, condensate, and mechanical stress, and are airtight.
The flue must ensure the minimum negative pressure established by current standards, with “zero” pressure considered at the fitting to the flue.
Unsuitable or incorrectly sized flues can increase the noise produced by combustion, cause condensation problems, and negatively affect the
combustion parameters. Uninsulated flues are a source of danger. The joint seals must be made with materials that can resist temperatures
of at least 250ºC. Suitable points for measuring the flue gas temperature and analyzing the products of combustion must be prepared in the
connection between the boiler and the flue.
For the cross-section and height of the chimney, refer to current local and national regulations.
5.5 Hydraulic connections
5.5.1 Supply water
The chemical characteristics of the system and top-up water are fundamental for the correct operation and safety of the boiler. The water must
be treated using suitable systems. The values shown in the table below can be used as a reference.
TOTAL HARDNESS ppm 10
ALKALINITY mg/l CaCO3 750
PH 8÷9
SILICA ppm 100
CHLORIDES ppm 3500
The water used in the heating system absolutely must be treated in the following cases:
- Very large systems
- Very hard water
- Frequent addition of water to top up the system
If it becomes necessary to partially or completely empty the system, it should be refilled with treated water. To control the volume of water refi-
lled, a meter should be installed on the pipe. The most common issues arising in heating systems are:
- Lime scale deposits
Lime scale accumulates at the points where the wall temperature is highest. Due to their low heat conductivity, lime scale deposits cause a
reduction in heat exchange. Even if they’re only a few millimeters thick, the heat exchange between the flue gas and the water is limited, which
increases the temperature of the parts exposed to the flame and causes cracks in the tube plate.
