Instruction 24-94484-4
Operation
4.4 Sampling Point
FORCED AIR FURNACE – For atmospheric burner
or gravity vented, forced air heating equipment
with a clamshell or sectional heat exchanger de-
sign, test each of the exhaust ports at the top of the
heat exchanger. The probe should be inserted back
into each of the exhaust ports to obtain a flue-gas
sample, before any dilution air is mixed in.
HOT WATER TANK – Domestic hot water tanks
with the ‘bell’ shaped draft diverter can be ac-
curately tested by inserting the probe tip directly
into the top of the fire tube below the diverter.
80% EFFICIENCY FAN ASSIST OR POWER VENTED
– Combustion testing of fan assist or power vented,
furnaces/boilers should be done through a hole drilled
in the vent immediately above the inducer fan.
90% EFFICIENCY CONDENSING – Condens-
ing furnaces/boilers can be tested through a hole
drilled in the plastic vent pipe (when allowed by
the manufacturer or local authority of jurisdiction)
or taken from the exhaust termination.
ATMOSPHERIC OR GRAVITY VENTED BOILER
– Boilers, which have a ‘bell’ shaped draft diverter
on top, should be tested directly below the diverter
through a hole drilled in the vent connector.
Forced Air Furnace
Hot Water Tank
Atmospheric or Gravity
Vented Boiler
80% Eff. Fan Assist or
Power Vented
90% Eff. Condensing
Undiluted Flue
Gas Sample Taken
Under Draft
Diverter in Top
of Fire Tube
O2, CO,
Stack Temp.
Combustion Air
Sampling Point
