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CHOOSING A DISTRIBUTION TUBE LOCATION
When installing a steam humidifier on a packaged rooftop unit application, there are two locations that can be
used to mount the steam distribution tube: supply plenum/duct (Location A) or the return plenum/duct (Location B).
Note: Wherever distribution tube is installed, there must be a minimum of 4.5” between top of tube and the duct
ceiling. Refer to Figures 12 and 13 on page 17.
Location A is the best choice because
:
• The distribution tube is humidifying 100% of the air
• The supply air temperature is typically higher than the return air temperature, allowing for better absorption
of the steam
Note: In applications using zone control products, the distribution tube must be installed upstream of all zone
control dampers to ensure that all zones receive humidified supply air
Choosing control device locations
• Install the high humidity limit switch (a recommended optional device) a minimum of 5’ (1.5 m) downstream
of the distribution tube.
• Install the Automatic Steam Humidifier Control in the return air duct a minimum of 6” upstream of the
distribution tube.
• Install the airflow proving switch in the supply air plenum.
OM-4043
FIGURE 11 – Placing a Distribution Assembly in a Rooftop Air Handler Application
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