Fan coil versus PTAC, for odor purposes

Fan coil unit

  • Usually hidden above the entry ceiling or in a vertical closet
  • Coil fed by building chilled and hot water, so it can stay wet longer
  • Condensate drains into a shared line that can back up
  • May draw some air from a ceiling plenum rather than only the room
  • Access often requires a ladder and removing a ceiling panel

PTAC

  • Sits under the window in plain view
  • Self-contained compressor and coil
  • Condensate handled in the unit's own base pan
  • Recirculates room air plus some outside air through the sleeve
  • Chassis can be pulled and swapped in minutes

Where odor hides in fan coil rooms

The drain pan under the coil is the usual suspect for a musty or sour smell. If the pan does not slope properly, or the condensate line is partly blocked, water sits and grows slime. That smell then rides out with every fan cycle.

Smoke odor behaves differently. A guest who smoked for several nights coats the coil, the blower and the insulation lining the cabinet. Fibrous duct liner or cabinet insulation can absorb smoke and is difficult to clean. In some designs a return path through the ceiling space pulls room air past wiring, framing and the back of the ceiling tiles, so residue lands there too.

Vertical risers in some towers stack fan coils on top of each other floor after floor. If one unit's drain backs up, neighbors on the same stack can notice musty odor at the same time, which is a clue the problem is in a shared line rather than one room.

What engineering can check in a fan coil odor room

  • Open the access panel and look for standing water or slime in the drain pan.
  • Check whether the condensate line flows freely; note any gurgle or slow drain.
  • Inspect cabinet insulation for staining, sagging or a strong smell when pressed.
  • Look at the coil face for matting, dust load or a tan film.
  • Check the filter; note its condition and when it was last changed.
  • Lift an adjacent ceiling tile and smell the plenum, if the design uses it as a return.
  • Ask housekeeping whether rooms above or below have similar complaints.

Matching the finding to the response

  • IfStanding water and slime in the pan, clean line once flushedThenClean and disinfect the pan, flush the line, and recheck the room after a day of cooling.
  • IfSame musty smell on several floors of one stackThenLook at the shared condensate riser and any traps or cleanouts before treating rooms one by one.
  • IfHeavy smoke residue on coil and insulationThenPlan coil cleaning and ask whether the cabinet liner should be replaced rather than treated.
  • IfOdor only in the ceiling space above the entryThenInclude the plenum surfaces and ceiling tile backs in the scope.

General information for Downtown Denver, not a quote or professional advice. In an emergency, call 911.