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10.13
COMMON FLUE SYSTEMS
The Lochinvar TTW can be installed on to a common flue system if required. The common flue system should be
sized to operate under a negative pressure of -0.03 to -0.10 mbar throughout the modulation range of the
appliance.
If a positive pressure common flue system is to be used, a proprietary recirculation prevention
device must be installed at the flue spigot of each water heater to prevent products of
combustion from re-entering the plant room.
10.14
CONDENSATE DRAIN
If the length of the flue system exceeds 6 metres, an additional condensate drain should be fitted. The discharge
pipework should include a suitable water trap to prevent products of combustion from entering the plant room or
drainage system.
11.0 AIR SUPPLY
If combustion air is drawn from outside the building, the water heater will operate as a room-sealed (Type C)
appliance. If combustion air is drawn in from the plant room the water heater will operate as a conventionally
flued (Type B) appliance.
The following information is based on single water heater installations only. If more than one water heater is being
used, BS6644 should be consulted to calculate the necessary requirements.
11.1
AIR SUPPLY THROUGH HUMID AREAS
When the supply duct is installed in a water heater room with humid air (for example: greenhouses), a double
wall supply duct or an insulated duct should be considered to prevent condensation on the outside of the duct.
It is not possible to insulate the internal air pipes of the water heater. Make sure that no condensate can be
formed on the internal air canals.
The air supply duct must be protected against rain, when it is installed on top of the roof.
11.2
PIPE HEIGHTS AND MUTUAL DISTANCES ON A FLAT ROOF.
Height A
This is the height of the air inlet that must have a cap to prevent rainwater entering
the system.
When in- and outlet are mounted on a flat roof, the inlet should be at least 60 cm
above the roof surface and at least 30 cm above the maximum snow level.
Example 1:
When the maximum snow level on the roof surface is 45 cm then height A should be
45 + 30 = 75 cm. This is more than 60 cm so this height should be 75 cm.
Example 2:
When the maximum snow level on the roof surface is 15 cm then height A should be
at least 15 + 30 = 45 cm. This is less than 60 cm, so the height should be 60 cm.
Height difference B
This should be at least 70 cm: the flue gas outlet should be at least 70 cm higher than
the air inlet and should be equipped with a conical outlet.
A single flue outlet on a flat roof should stick out at least 100 cm from the roof
surface.
Distance C – mutual horizontal distance at roof level
This should be at least 70 cm.
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