Air Conditioning condensate drains, condensate pumps, and their proper installation
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Sewer Gas Hazards at Air Conditioners

[Example air conditioning system inspection report language]: *** Safety Recommendation: this condensate line is connected to the house drain/vent piping - risking possible bacteria or even dangerous sewer gases entering the building air handling system.

Good practice (and some building and mechanical codes) includes a moisture trap (just as with other plumbing drains) and routing of the condensate to a wet drain line or preferably outside to discharge into the gutter system or to the ground.

Sewer gases include methane which is an explosive gas. We don't want methane nor bacteria in our air conditioning system.

Here is a second example of improperly connected air conditioner condensate drain lines to a plumbing vent: the condensate line is connected to the house drain/vent piping; according to some experts and plumbing codes this is an improper plumbing connection, and for some lines there also is no condensate trap in this plumbing arrangement, risking possible bacteria or even dangerous sewer gases entering the building air handling system.

Good practice includes a moisture trap (just as with other plumbing drains) to help prevent this problem. Our understanding is that despite this very common installation found in our area, this is an improper plumbing connection which is dumping liquids into plumbing lines intended for dry-use only. Correction by a qualified plumber does not usually involve significant expense.

HEALTH NOTE: Condensate drains should not be connected directly to a house drain as bacteria can grow back up the condensate line to contaminate building air, or sewer gases may be drawn up the drain and into the building air when the blower fan is operating.

Air conditioner condensate spillage in crawl spaces: is sometimes seen, especially if it's a dirt-floor crawl space.The installer probably figures the condensate will just "go away" through the soil exposed in the crawl area.

What s/he failed to consider is the risks of a legionnaire's infection or a mold problem caused by spillage of water into an indoor, and in this case confined and rarely-inspected space.

Air conditioner condensate spillage down building walls: such as the condensate from this attic air handler can stain the building walls and is simply ugly.

An expert HVAC technician might also have something to say about those rust stains themselves - we may be looking at rust from inside the air handler, indicating that A/C condensate is spilling and leaking around inside the unit - perhaps we're actually looking at a hidden mold problem in this building - more investigation would be appropriate.

Safety Hazards of Air Conditioning System Condensate Leaks Onto a Furnace Heat Exchanger

This photograph shows a typical point of disposal of air conditioning condensate outdoors, onto the ground. This A/C condensate line originated at the air handler in the building attic, though at some installations we could be looking at condensate from a condensate pump located in the building basement.

There's basically no issue with disposing of condensate at this location, though this particular photo shows two more subtle points to watch:

1. There is some soil subsidence going on where the condensate is dripping, telling us that the soil around the foundation is fresh, loose backfill. Watch out that the air conditioner compressor/condenser unit does not begin to tip as this backfill settles further from the soil subsidence that will accompany rainfall, snowmelt, and time. Concerns for tipping A/C condenser units are discussed at Air Conditioner Compressor & Condenser Installation Errors.
   
   
2. Foundation leaks: The second more subtle point to watch that has evidence in this photo is that little shrinkage crack we see in the poured concrete foundation right where the A/C condensate is dripping. We might see water leaks into the building interior at this point if the foundation is visible indoors, or if the wall has been covered with finish materials we might have a mold problem. I wouldn't go on to cut open such a wall to investigate this particular case further without other corroborating evidence. More about foundation crack diagnosis is available at How to Diagnose & Evaluate Vertical Foundation Cracks.

This photograph shows what seems to us to be a sloppy installation of air conditioner condensate drainage.

The installer has sent the condensate drain line outdoors (fine) through the building eaves or soffit (OK) but left the condensate drain pipe terminated where it drips onto a lower roof, splashing up and staining building siding, possibly creating a wear spot on the roof shingles, and thus perhaps a roof leak before the rest of the shingles are ready for replacement.

Condensate drains routed to hidden locations: What about installers who route a condensate drain to some hidden location? The drains in this photo might be ok, or maybe not - it depends. If they disappear into an inaccessible or not readily visible location such as a crawl space the system is asking for trouble - such as a wet moldy crawl space.

If the drains appear outside or at some other visible location we're in good shape. In this particular case, the air conditioning system for the computer center of a large college was draining onto the floor of a utility room where condensate ran along drywall and then across to a floor drain. The drywall gave us a little area of mold to clean up but luckily nothing of any consequence. We could see the ends of this drain if we looked long enough.

The discharge point of all of the air conditioning system condensate drain lines, that is the system condensate drain and the air conditioner condensate overflow pan drain, must be readily observable. (Ref. Uniform Mechanical Code Sec. 1205 and Sec. 510. Condensate overflow pan is suggested for attic space per UMC (Uniform Mechanical Code) Section 1205.)