Minerals that are naturally found in water cause the water to
be electrically conductive. Water conductivity is measured in
micro Siemens per centimeter (uS/cm). Mineral content, also
described as “water hardness” is usually measured in grains per gallon. Because of the variety of minerals that are found in water, there is no
direct correlation between water hardness and conductivity, but generally the higher the mineral content, the higher the conductivity.
The Model 800 Canister Steam Humidifier is designed to operate on water with conductivity between 125 and 1,250 uS/cm. This correlates
loosely with water with hardness between 3 and 36 grains/gallon. Water that is considered “hard” and also softened water work well in the
Model 800. The humidifier will make steam when plumbed to low-conductivity water but it takes longer to reach nominal capacity.
With low conductivity water, it may take the Model 800 humidifier one week or more of operation to reach rated capacity,
especially if it is wired to operate on 120 volts. When operating on 240 volts, the Model 800 usually will reach nominal capacity
within a few hours, even with lower conductivity water.
As water in the canister boils and turns into steam, minerals are left behind. The remaining minerals, if they remain in solution in the water,
increase the conductivity of the water. Minerals also deposit onto the submerged portions of the electrodes rendering those areas ineffective. As
this occurs, the level of water in the canister rises to expose uncoated electrode surface.
SPECIFICATIONS & DIMENSIONS
TABLE 1 – Specifications
Voltage kW Maximum steam capacity Nominal Current draw (amps) Humidifier unit operating weight
gal/day amps lbs
120V 1.4 11.5 11.5 23
208V 2.4 20.5 11.5 23
240V 2.8 23.3 11.5 23
The Aprilaire®Model 800 Canister Steam Humidifier delivers
humidity in the form of steam to the conditioned space via
the HVAC system duct or optional Aprilaire Model 850 Fan
Pack. The humidifier generates steam by energizing two
electrodes that extend into a canister of water. Current
flowing between the electrodes causes the water to boil,
creating steam. Water is introduced to the humidifier through
a fill valve to a fill cup located in the top of the cabinet. The
fill cup serves as an overflow reservoir and provides an air
gap between the humidifier and water source. The steam
canister is filled from the bottom. The canister is seated
in a drain cup assembly which includes a drain valve. The
drain and fill valves work together to maintain water level
in the canister to deliver the rated steam capacity based
on the electrical conductivity of the water and to temper
drain water. See Figure 1 for representation of fill and drain
system and canister.
Steam is delivered into the airstream through a dispersion
tube mounted in the HVAC system ductwork. Openings in the
dispersion tube are fitted with “tubelets” which extend into
the center of the tube. The design of the dispersion tube and
tubelets distribute steam over a wide area in the duct and
direct any condensed moisture back into the steam hose.
PRINCIPLES OF OPERATION
FIGURE 1 – Fill and Drain System and Canister
90-1522
Outlet
Drain
Supply
Water
Drain Cup
Drain Valve
Canister
Electrodes
High Water
Level Sensor
Flow Control
Orifice
Inlet
Fill Valve
Overflow
Fill
Fill Cup
WATER QUALITY
3
