13
Operations
Combustion and Ventilation Air
Properly sized vents are vital for the safe and efficient
operation of a pressure washer installed in a confined
space. When combustion and ventilation air are
supplied from inside the building, each opening must
have an area of one square inch for every 1,000 BTUH
input. When combustion air is supplied from the
outside, each opening must have an area of one
square inch for every 2,000 BTUH for horizontal ducts
and one square inch for every 4,000 BTUH for vertical
ducts (refer to NFPA 54).
The purpose of venting a gas pressure washer is to
completely remove all products of combustion and to
vent gasses to the outside air without condensation in
the vent or spillage at the draft hood (except in cases of
downdraft or poor stack conditions). To assure correct
venting, use a strong, gas-tight insulated pipe with a
cross section equal to that of the flue collar or draft
hood outlet and of sufficient vertical height.
During vent installation, avoid sharp turns, long hori-
zontal runs and improper pitches. Maintain proper
support of vent connectors and joints, observe clear-
ances from all combustibles and top the vent outlet with
an approved cap.
Type “B”, due to its temperature rating, can only be
used with natural draft pressure washers. A “B” vent is
designed for exhaust temperatures not to exceed
470°F (245°C).
All venting installations must conform to local codes. In
the absence of local codes, refer to “National Fuel Gas
Code” NFPA 54 and be constructed of materials
approved by the Uniform Building Code.
The pressure washer includes a collar that will mate
with standard HVAC ducting. The user will be respon-
sible for installation of an exhaust stack. The exhaust
stack should include a Draft Diverter/Inducer, Damper,
Sampling Port and Rain Cap. An adapter can be
installed between the collar and stack to adjust the
diameter from 10” to 8” or 12” to 10”.
Size the stack according to the following (see also
applicable local and national standards regarding
installation of gas-fired appliances):
•
3.5 to 4.4 gpm 10” Collar 8” Stack
•
4.5 to 5.5 gpm 10” Collar 10” Stack
•
6.3 gpm 12” Collar 10” Stack
•
8 – 10 gpm 12” Collar 12” Stack
Draft Diverter/Hood
The draft required to vent
combustion gases is created by the heat inside the
pressure washer coil. A draft diverter helps improve
draft into the stack without pulling more air through the
combustion box and decreasing combustion efficiency.
The draft diverter can also help prevent back drafting
that can inhibit combustion. The draft diverter should be
installed a minimum of 36” above the flue collar.
Power Vent (Draft Inducer)
If this machine is going to
be installed on a 90° or extended exhaust vent run
length which may restrict air flow it is recommended
that a contractor install a power vent. When a
contractor has found it impossible to vent straight
through the roof power venting is recommended to
help eliminate exhaust restriction of this natural draft
machine. This draft inducer (power vent) must be
installed by a licensed contractor who can calculate
size, operation connections and associated damp-
eners. Since we are a manufacturer and not a licensed
contractor and as such we are unable to make recom-
mendations for suitable make and model of power
vents and compliance with local building codes.
Damper
An exhaust stack can reduce thermal effi-
ciency by drawing in too much combustion air. This can
be controlled by adding a damper just below the draft
diverter. 8.753-473.0 - 8" Damper, 8.753-474.0 -10"
Damper, 8.753-418.0 - 12" Damper.
NOTE: Closing the damper can create high levels of
CO in the exhaust. Adjustments to the damper should
only be performed by a trained technician using a flue
gas analyzer. If an analyzer is not used the damper
should be set in the fully open position.
Draft Diverter
Required
8.717-728.0 8"
9.801-040.0 10"
8.717-730.0 12"
Landa VNG Operator’s Manual 8.913-939.0 - AB
Illustration showing air openings necessary
to supply air for combustion when installed
in an enclosed room.
