Photograph of  this unusual condensate drip system Condensate Drains, Piping, Pumps
Inspect & Repair HVAC Condensate Piping & Drains

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Air conditioner, heat pump & condensing boiler or furnace 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, heat pump, or condensing boiler or furnace condensate piping, drains, & 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.

We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

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. [Click to enlarge any image]

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

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.


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.


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

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 © D Friedman at

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

Reader Question: our wall-mounted split system air conditioner leaks condensate down the interior wall

We noticed water stains and wet spots on the wall below our wall-mounted split system air conditioner. But condensate is also coming out of the drain line on the roof. What might be wrong? - Ed.

Reply: Common defects that cause leaks or blockages in wall-mounted air conditioner condensate drains

Air conditioning drain line installation © D Friedman at Check the following sources of condensation leaks at or near a wall-mounted air conditioner::

If the wall mounted air conditioner is not level, condensate may collect in its internal drain pan but may overflow the (relatively shallow) condensate pan edges before reaching the condensate drain opening. Check the unit for level, and watch out: the plastic cover may not be dead straight - it's the unit itself that should be level for the condensate drain pan to work properly.

The photo showing flexible air conditioner condensate piping is explained at SPLIT SYSTEM AIR CONDITIONERS & HEAT PUMPS.

That white line is the condensate drain headed from the wall-mounted unit (not shown) to outdoors.


Continue reading at CONDENSATE LEAKS or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see these

HVAC Condensate Articles

Suggested citation for this web page

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


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