CHOOSING A LOCATION
DISPERSION TUBE
When choosing a location for the dispersion tube three things must be considered: Location in duct, elevation with respect to the humidifier, and
distance from humidifier to dispersion tube.
Duct Location and Absorption Distance
The preferred location for the dispersion tube is in a supply duct because higher temperature air will absorb moisture more readily. The
dispersion tube must be in a straight section of duct far enough upstream of any obstruction or bends in the duct to allow the steam to be fully
absorbed, preventing condensation in the duct. The exact distance from obstructions in the duct depends on air temperature, RH set point, and
airflow velocity in the duct. Most installations can use an absorption distance between 24 and 36 inches, however if there are obstructions in
the ductwork use Table 3 to determine the appropriate absorption distance. Size absorption distance based on the lowest temperature,
lowest air velocity and highest humidity that the system will see. When installing the humidifier in a system with variable speed blower,
determine absorption distance based on airflow at the lowest speed. Operation during AC calls is not recommended because of the potential for
condensation in the ductwork. If humidifier operation is needed during AC operation, make sure absorption distance is adequate. If absorption
distance is insufficient, configure controls to lock out humidifier during the AC calls and use the blower activation feature to allow the humidifier
to run with the blower only. Call Aprilaire Tech Support at 1-800-334-6011 for additional information on absorption.
The dispersion tube must be mounted with the plate on a vertical surface with the tube angled up as shown in Figure 3. The steam outlets must
face up regardless of the airflow direction in the duct. The plate is labeled “UP”to indicate proper orientation. On horizontal duct runs install the
dispersion tube low in the duct, on vertical runs center the tube on the duct.
If the dispersion tube is mounted on insulated ductwork, make sure insulation is not more than 2” thick at tube location to prevent insulation
from blocking first steam outlet.
Note: If two dispersion tubes are installed in one duct, double the dispersion distances. If three dispersion tubes are installed, triple the
dispersion distance. Position dispersion tubes so one does not discharge directly onto another.
INSTALLATION INSTRUCTIONS
CAUTION
Each humidifier requires its own steam hose and dispersion tube. Do not connect steam hoses from more than one humidifier
together. Back-pressure from one humidifier can lower the water level in the canister in the other humidifier and cause
operational problems.
Do not install the dispersion tube in a duct with greater than 2 in. wg static pressure. High duct pressure can cause back-
pressure in the canister which can result in unstable unit operation.
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