General Instruction; Description; Boiler Schematic - Keston 50 - GC Installation And Servicing Instructions

WD50/2/1997 Chapter 1 : General Instruction
1.1

DESCRIPTION

The Keston Condensing Boiler is unique in its concept and design. While the application
for which the boiler was designed is the same as those which other boilers are used the
Keston boiler has the added advantage of very high efficiency, and small diameter plastic
flue which can be extended to 10 metres horizontally or vertically.
The Keston uses a high power combustion blower to deliver a pre-mix of gas and air to a
downward firing burner in a high efficiency, single pass heat exchanger.
Normally the combustion temperature of the air gas mixture is around 1800
Keston achieves combustion at an amazing 1000
down to an incredible less than 5 p.p.m.
The flue system is room sealed and fan powered. The ignition is direct spark and fully
automatic. The boiler housing is not waterproof. The boiler should be installed in a
position where it will always be dry. A small air intake point is incorporated within the
appliance cabinet to ensure that the interior of the cabinet is maintained under a slight
negative pressure. This is a safety feature to ensure no products may leak out of the
cabinet into the installation space.
The boiler is suitable for connection to open vented or sealed systems. The system must
be pumped central heating or pumped central heating with combined indirect domestic hot
water. Gravity circuits must not be used.
The boiler has a primary heat exchanger which, through its combustion chamber and
corrugated coil, transfers the heat produced in the hot gases of combustion process into
the circulating water. Head characteristics of the boiler coil must be taken into
consideration when calculating the pump size.
The Keston boiler is not a high water content boiler and does not contain the metal mass,
or water volume, of a cast iron or steel boiler. This boiler is of low mass and low water
content and therefore responds faster when there is a call for heat. This feature requires a
higher water pumping rate through the boiler otherwise localised boiling will occur within
the boiler.
Allow a pressure drop through the boiler of 3.2 ft head and a water flow of 4.2 gallons (19
litres) per minute for the Keston 50, 4.3 ft head and 5 gallons (23 litres) per minute for the
Keston 60 and 9 ft head and 6.7 gallons (30.5 litres) per minute for the Keston 80.
The boiler selected must be sized relative to the total calculated heat loss of the building.
The boiler rated output should not be greater than the total required to make up the
calculated heat loss plus the heat required to provide domestic hot water. If there are
special conditions such as excessive domestic hot water usage consult the manufacturer.
1.2

BOILER SCHEMATIC

Air is drawn into the boiler through a 40mm (BS5255) muPVC pipe. The air flow is proved
by a differential pressure across the air control orifice.
Gas is mixed with combustion air at the inlet to the fan. The gas flow is regulated by an
orifice located in the housing downstream of the gas valve.
Installation & Servicing Instructions
The Keston 50, 60 & 80 Condensing Boiler

1. GENERAL INSTRUCTION

Page : 1
o
C thereby reducing the NO
s
o
C but the
emissions
x