Where the water comes from

In most Highlands Ranch homes with central air, the evaporator coil sits on top of the furnace in a basement mechanical room. As warm air passes over the cold coil, moisture condenses and drips into a pan, then runs through a small PVC line to a floor drain, a sump pit, or a condensate pump.

Over time the line can fill with slime and debris, and the water backs up. Some systems have a float switch that shuts the air conditioner off when the pan fills, but many older installations do not. Condensate pumps can also fail, especially after years of summer use.

Because the furnace room is often unfinished and rarely visited in summer, an overflow can wet the slab, the bottom of adjoining finished walls, and the insulation inside the coil cabinet for weeks.

What you are seeing and what it suggests

  • IfWater on the floor around the furnace during summer onlyThenSuspect the condensate line or pump. Check the pan and the line outlet.
  • IfRust or staining on the furnace cabinet below the coilThenThe pan may be overflowing or cracked. Have an HVAC technician inspect it.
  • IfMusty smell from supply registers when the AC startsThenThere may be growth on the coil or in insulation near it. Ask for a coil and plenum inspection.
  • IfDamp drywall on the other side of the furnace room wallThenWater has spread under the wall. Moisture readings and possibly removal of the lower drywall are needed.
  • IfWater in the same spot in winterThenLook at the water heater, humidifier or high-efficiency furnace drain instead.

Spring start-up checks

  • Find where the condensate line ends and make sure the outlet is clear
  • Pour a cup of water into the pan access, if reachable, and confirm it drains
  • Test a condensate pump by lifting its float or adding water
  • Ask whether a float safety switch is installed on the pan or line
  • Replace the furnace filter so airflow over the coil stays normal
  • Keep stored items off the floor near the furnace

Ask the HVAC technician

  1. Is the condensate pan intact and sloped to drain?
  2. Is there a float switch, and does it work?
  3. Do you see growth on the coil or the cabinet insulation?
  4. Where does the condensate pump discharge, and is that location appropriate?

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