Discharge Of Combustion Products (Fig. 7); Hydraulic Connections; Supply Water; System Feed/Return Pipes - Ferroli PREXTHERM RSH 950N Instruction For Use, Installation And Assembly

5.4 Discharge of combustion products (Fig. 7)

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 con-
densation 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 oper-
ation 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 re-
filled, 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.
- Corrosion on the water side
Corrosion of the metal surfaces on the water side of the boiler is caused by the dissolution of iron into its ions. The presence of dissolved gases,
particularly oxygen and carbon dioxide, plays an important role in this process. Softened and/or demineralized water provides protection against
deposits, but not against corrosion. The water must therefore be treated with corrosion inhibitors.

5.5.2 System feed/return pipes

The dimensions of the feed and return pipes for each boiler model are indicated on the DIMENSIONS table. Make sure the system has a suf-
ficient number of vent openings.
The boiler fittings must not support the weight of the connection pipes to the system. Appropriate supports must be installed for this purpose.

5.5.3 System fill/drain pipe

For filling and draining the boiler, a cock can be connected to fitting T4 on the back (see DIMENSIONS, Fig. 3).

5.5.4 Pipes, expansion vessel and safety valves

PREXTHERM RSH N boilers are suitable for operation with forced water circulation, with the expansion vessel open or closed. An expansion
vessel is always required to compensate for the increase in water volume due to heating. In the first case, the height of the hydrostatic column
must be at least 3 meters above the boiler body. Its capacity must be sufficient to contain the increase in volume of all water in the system,
between the surface of the water in the vessel and the overflow pipe. Tall, narrow vessels are preferable, as they ensure minimum contact
between the water surface and the air, thus reducing evaporation. In the second case, the capacity of the closed expansion vessel must be
calculated considering:
- the total volume of water contained in the system
- the maximum operating pressure of the system
- the maximum operating pressure of the expansion vessel
- the initial pre-charge pressure of the expansion vessel
- the boiler's maximum operating temperature (the maximum temperature on the thermostat fitted on the panel is 90ºC; use 100ºC to perform
this calculation).
32
EN
cod. A73020821 - 2023-09
PREXTHERM RSH N