Thursday, February 22, 2018

Autoflo Model SC-15




  • Patented air diverter eliminates the need for a bypass
  • One (1) opening on the plenum
  • Uses minimal water and electricity
  • Durable fiberglass cabinet resists rust, corrosion, and warping
  • Output capacity of 17.0 gallons per day (GPD)


  • Size: 13-3/4 in. high x 13-3/4 in. wide x 6 in. deep
  • Plenum Opening: 11 in. high x 11 in. wide
  • Bypass Opening: None Required
  • Solenoid: 24 VAC, 7.5 watts
  • Evaporative Pad: 11-1/2 in. high x 11 1/2 in. wide x 1-5/8 in. deep

Moisture Output Capacity

  • Moisture Output Capacity
  • LBS. Per Hour: 5.92
  • Gallons Per Hour (GPH): 0.71
  • Gallons Per Day (GPD): 17.0


The AUTOFLO Model SC-15 uses the evaporative principle to add moisture to the warm air heating system.  Upon a demand for humidity from the humidity control, the water solenoid valve opens and water flows in at the top of the media pad and is evaporated, as warm air passes through the media pad.  When the moisture laden air re-enters the duct it is mixed with dry air already flowing through the duct.  This moisture laden air gradually increases the relative humidity level in the home.



Refer to the rating plate on the furnace for minimum clearances to combustible construction.  All parts and connections of an AUTOFLO humidifier must be installed outside of the minimum clearance requirements for rear, top, sides, and flue of furnace.  Do not install where humidifier or water connections may be exposed to freezing temperatures or outside weather.  Attic installations are NOT recommended.  If you have central air conditioning, carefully plan the location of the plenum opening to prevent damage to the cooling coil or other components inside the duct.


The AUTOFLO model SC-15, is to be mounted on the supply duct of the furnace only.


The humidistat can be mounted on the cold air return duct to sense the cool dry air returning to the furnace.  It can also be mounted  on an interior wall near the furnace thermostat as well.  The electrical connections and basic wiring are the same for duct mounted or wall mounted humidistats.


CAUTION:  Installation should be performed by qualified personnel only.  Use eye protection and gloves when drilling and handling sheet metal.  All work must be performed to local and national codes and ordinances.  Use multi-conductor 18 awg. solid copper wire.  Provide over-current protection as required.  DO NOT omit the drain or overflow tubing. Turn off power to the furnace before installing the humidifier.


Turn off power to the furnace before installing the humidifier.  Test fit the SC-15 housing on the side of the warm air plenum.  Before proceeding, verify that adequate clearances are available for servicing the media pad.  There must also be adequate room (5 1/2 inches) inside the plenum for the louver.  If necessary, relocate the unit.  Use a plumb line or a level to make sure the housing is level.  With a permanent marker outline the inside edge of the housing.  Also mark the twelve holes to be drilled.  Center punch and drill al twelve holes as indicated by the marks.  Drill or punch a starter hole and then use tin snips to cut out the rectangular shaped opening.  The opening should be 1/8 inch larger on all four sides than what was marked.


Hold the housing next to the duct and start four #8 x 3/4 inch long sheet metal screws through the holes in the bottom edge of the humidifier.  With these four screws started the unit should remain in place while starting the other eight screws.  With all twelve screws started they can now be tightened.  With the housing mounted the louver can be installed.  This should be done by rotating the louver to the proper position depending on the direction of airflow.  The airflow should enter into the curved multi-louvers and exit out of the large opening.


The transformer should be wired in parallel with the furnace blower motor line voltage.  This will allow the humidifier to run only when there is a call for fan.  The transformer is designed to be attached to a 4 inch square outlet box.  The electrical box must be mounted and wired in accordance with local building codes and the National Electrical Code.  SHUT OFF THE POWER TO THE FURNACE BEFORE PROCEEDING! NOTE1: Check wiring in furnace for humidifier (HUM) terminals.  If present, check to see if it is 120vac or 24vac.  If it is 120vac, connect the transformer primary leads to these terminals.  If it is 24vac, you do not need the transformer.  Simply connect one side of the humidistat to one HUM terminal and the other HUM terminal to the solenoid valve of the humidifier.  Then make the last connection of the solenoid valve to the humidistat.  If you are using the transformer you will need to connect the 24vac common from the transformer to one of the solenoid valve wires and then the 24vac hot from the transformer to the humidistat.  Then from the humidistat to the other wire on the solenoid valve.  Make sure not to route wires where they can be burned or chaffed.  See example wiring solutions.


With the humidistat set to its highest setting the humidifier solenoid should open shortly after the furnace blower is activated.  If the solenoid does not open refer to the troubleshooting guide.

CAUTION: Check the transformer, the solenoid valve and humidistat as well as all field wiring connections as they could be at fault.

A qualified Electrician should be consulted to determine if 24 vac is present at the solenoid and at the humidistat, and that line voltage is present at the transformer.


The Autoflo Humidistat should be installed as described in the installation instructions supplied with the humidistat.


Water supply for the humidifier should be taken from a nearby hot water line but cold water is acceptable.  All water connections should be made at ground floor level.  Do not use any water line served by a water softener.  A water softener is not a de-mineralizer.  It merely exchanges various hard-ions for soft-ions in the water.  These soft-ions or minerals, will build up in the transfer media in the humidifier, causing the need for more frequent servicing.  The evaporation of softened water may also produce a white powder which may be carried in to the duct system and ultimately in to the home.  The saddle tapping valve should be mounted on top of, or on the side of the water line.  If the valve is installed on the bottom of the water line it could clog with sediment from the water line.  Refer to the instructions on the saddle valve package and proceed as follows.  For copper water lines the valve is self piercing.  Mount the saddle valve to the top or side of the water line, then turn "T" handle to the clockwise until it stops to pierce and seat the valve to the pipe.  Open to flush the valve and close it again.  Then connect plastic water line from the valve to the humidifier making sure not to kink it or run it near any hot flue pipes.  Connect water line to valve and humidifier with supplied hardware.  Now open the saddle valve turning the tee handle counter clockwise until fully open.  Check for water leaks and repair as necessary.  Attic installations are not recommended.


Connect the 1/2 inch plastic tubing to the drain spout and secure it.  The spout is located at the bottom of the housing.  Keep the tubing as short as possible and avoid sharp bends.  The drain line should be routed on a continuous downward slope and into a suitable drain.  WARNING:  failure to connect the drain tubing could result in a flood.


Make sure the evaporative pad is positioned in the door correctly.  The black mark on the edge of the pad indicated the top.  The pad slides into the door and rests against the four legs located inside.

Position the bottom edge of the door in the tray located on the lower opening in the housing.  Then simply push the top of the door closed until it has snapped into place.  To remove door just push down on the two tabs located at the top of the door and pull the door away from the housing.


Most people feel comfortable between 35% to 45% RH, but the proper relative humidity for your home depends upon many factors such as outside air temperature, type, and placement of insulation, vapor barrier, effectiveness of weather stripping, type of windows and doors (including frames and jams), and whether storm windows and doors are used.  With all of these variables it is nearly impossible to recommend a proper humidity setting.  The best humidistat setting is one that you are comfortable with.  Also, as the outdoor temperature fluctuates, it may be necessary to adjust the humidity level a few times during the heating season.  Refer to the "Relative Humidity Chart" as a starting point for your proper humidistat setting.  Generally, in a tighter and better insulated house, the humidistat may be set higher than in a drafty, un insulated house.


Cold air cannot hold as much moisture as warm air.  Any cold drafts or cold-faces such as windows and doors (including frames and jams) may cause water vapor to condense at these points.  Also, if your home is well-insulated and weather-stripped but lacks effective vapor barriers, water may seep through the walls and ceilings.  This moisture may condense either inside or outside the walls or in the attic.  If any of these conditions are observed, the humidity level should be reduced before water damage occurs.


Suggested Humidistat Settings



+30o F


+20o F


+10o F


+0o F


-9o F




All power humidifiers require some maintenance to keep them operating at peak performance.  The autoflo SC-15 humidifiers have been designed to simplify required maintenance.

1.  Semi-annual replacement of the evaporator pad.

2.  An annual cleaning, general inspection, and shut down of the unit at the end of the heating season.

3.  The evaporative pad should be replaced when it starts to look white and chalky.  replace it with a catalog #SC-EP pad.



 1. Model SC-15 Humidifier
 2. Small parts bag containing:
     a. Two #8 x 3/4 in. sheet metal screws
     b. Twelve #8 x 3/8 in. sheet metal screws
 3.  Saddle tapping valve kit
 4.  24 volt humidistat
 5.  24 volt transformer
 6.  1/2 in. drain hose
 7.  1/4 in. plastic tubing
 8.  Evaporative media pad
 9.  Owner's manual



 1.  Relay, with 120 volt current sensing
      coil for furnaces with multi-speed
      blower motors.
 2.  4x4 wire box to mount transformer and
      enclose line voltage connections.
 3.  #18 awg. thermostat wire to make up any
      and all 24 volt connections
 4.  1/2 in. drain hose clamp.

 Owner's Manual
Due to continuous product research and enhancements, BestAir PRO reserves the right to change product components and specifications without notice.
Copyright 2010 by BestAir PRO, Inc.