Photograph of  this unusual condensate drip system A/C or Heat Pump System Condensate Drains, Piping, Pumps
Inspect, Diagnose, Repair Guide

  • CONDENSATE HANDLING - home - CONTENTS: Air Conditioning Condensate Handling Defects - when & how to inspect the air conditioner condensate drain system to find A/C condensate piping, leaks, hazards
  • POST a QUESTION or READ FAQs about recognizing defects in air conditioner and heat pump condensate drain line piping, connections, traps, or disposal destination

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Air conditioner condensate handling & drainage defects: this air conditioning repair article discusses the inspection, diagnosis, and repair of air conditioning condensate drainage systems, including condensate leaks, condensate piping, traps, drains, condensate pumps, and the detection and hazards of air conditioning system condensate leaks in buildings. Condensate leak water health and safety concerns are also reviewed.

This document describes the inspection and repair of condensate handling systems for residential air conditioning systems (A/C systems) to inform home buyers, owners, and home inspectors of common cooling system defects.

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Condensate Handling: Air Conditioning / Heat Pump Condensate Handling Defects

Schematic explains how air conditioning condensate is handled and disposed-of properly (C) Carson Dunlop Associates

Improper handling of air conditioning system condensate is one of the most commonly reported set of A/C system defects. Condensate problems can lead to leaks into the building, costly mold or insect damage, or even to complete A/C or heat pump system shutdown.

Perhaps we see lots of air conditioning condensate leaks and related problems in part because these defects are easily observed visually, and perhaps also because some A/C installers do not follow basic plumbing and building code requirements for handling the discharge of the condensate produced when an air conditioning system is operating.

Sketch courtesy of Carson Dunlop Associates.

Condensate leaks or discharge errors (such as the drips into the dog bowl and cooking pot in this attic) present several risks of ugly surprises in buildings.

Here are some inspection tips that can avoid a condensate leak or even a costly mold problem in the air conditioning system air handler, duct work, or in the building itself:

Locate how & where condensate discharge is carried for final disposal

AC condensate line emptys onto roof and into gutter (C) Daniel Friedman

  • A flexible plastic condensate drain line may be routed through building walls, ceilings, floors, at some installations such as split system wall-mounted air conditioners and heat pumps. At SPLIT SYSTEM AIR CONDITIONERS & HEAT PUMPS we describe the routing, slope, and protection from damage for in-wall condensate drain lines.

    Our photo (left) shows the condensate drain termination for a roof-mounted split system air conditioner - the white plastic condensate drain exits the building wall and is carried to the roof surface next to the roof-mounted inverter or compressor/condenser unit for the cooling system.
  • a plastic line draining outside to an approved drain destination - see CONDENSATE DRAINS
  • a floor drain
  • a sump pit
  • a hole in the floor
  • a reservoir lift pump (CONDENSATE PUMPS) which pipes condensate to: (a properly connected building drain; something else)
  • the pump exit line is taken to the house main waste line
  • a dirt floor or crawl space (a bad idea, asking for mold or insect damage)
  • Problems with condensate drains themselves are detailed at CONDENSATE DRAINS
  • Condensate drains or swamp cooler leaks or drains may leave WHITE STAINS on ROOFS

Check for a clogged A/C condensate drain line trap

Condensate drain line trap requirements (C) Carson Dunlop Associates

One of the most common causes of air conditioning or heat pump condensate leakage and overflow is a clogged condensate drain line trap. And if the secondary or emergency condensate handling system is absent or defective, the result can be costly leak damage to the equipment or to the building.

Carson Dunlop Associates' sketch (left) illustrates the requirement for a trap on the A/C condensate primary drain line.

Look out for a missing condensate overflow pan or drip tray:

If there is no overflow pan under the air handler, especially in units installed on upper building floors or in an attic, when the condensate drain clogs or the condensate pump fails you can expect to have leaks into the building and possibly costly mold or water damage.

See DRIP TRAY DEFECTS for details.

Look out for an improper condensate overflow pan drain connection

A condensate pan should have its own independent drain to an approved location. Otherwise, for example if it shares the main condensate drain pipe, you have not gained much protection. An alternative to a drain on a condensate overflow pan is the installation of a Float Switch on Condensate Tray that will turn off the system if water is detected. See CONDENSATE DRAINS.

Look for corrosion or water stains on floor surfaces around the equipment

Check the condensate drip pan and at bottom of the "A frame" cooling coil, indicating that the drain may need cleaning and more important, indicating that the condensate is leaking out of the equipment or drains and not being carried to an acceptable disposal point.

Links below continue with detailed discussions of condensate handling components, defects, cleaning, maintenance, and repairs.

Periodic Inspection of the Air Conditioner Condensate Drain System - Some Suggestions

Condensate drain line crimp (C) Daniel Friedman

Question: how and when do we inspect the condensate drain?

I can't find a description of the method for inspecting the drain pipe leading out from the drain pan under the condenser coils.

I have been told that this pipe commonly blocks up and causes problems and that inspecting it is a part of a HVAC maintenance program. Would you describe for me, or maybe add to your site, how often and how this drain line should be inspected and maintained?

- R.B. Chattanooga, TN.,

Reply: check for a clogged condensate drain line trap, crimps in the line, or clogs in the line; check that the line is routed to a proper destination

The condensate drain line, trap, and evidence of blockage, leaks, overflow, or improper piping should be part of annual air conditioning system service, or should be performed immediately if there is evidence of a condensate spill or leak. It only takes a quick look by an experienced service technician to see trouble. Here are some signs of trouble that a visual inspection of the condensate drain system might pick at an inspection:

Condensate Leak (C) D Friedman

  • Visual inspection for obvious debris at opening to the condensate drain, inside the air handler
  • Visual inspection for evidence of condensate overflowing out of or backing up in the air handler when it should be passing out the drain - such as is shown in our photo at left.
  • Visual inspection for condensate backup or spillage such as presence of condensate in an overflow pan
  • Tripping off of the float switch in the overflow pan if you have one
  • Some condensate drains have a removable cap on the trap to inspect in and clean the trap - traps are usually where blockages occur
  • Visual inspection of the entire drain line to see its routing - and to assure it's taken to a proper destination. Our photo at the top of this section above shows a crimped condensate drain pump line - we were a bit worried that with even the slightest additional movement in this soft flexible plastic tube (connecting the condensate pump to a nearby laundry drain) would prevent the pump from working properly.
  • Failure of any condensate to come out of the exposed end of the condensate drain line when the A/C system has been running during hot, humid weather
  • If a condensate pump is installed, overflow of condensate out of the pump housing

Check out the articles listed below for more detail about each type of condensate drain system defect.


Continue reading at CONDENSATE LEAKS or select a topic from the More Reading links shown below.

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CONDENSATE HANDLING at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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