Improper HVAC Condensate Piping & Disposal

Condensate drain SNAFUs

Condensate Drain Leaks & Clogging: Improper Slope

Our photo (left) shows a white flexible tube used as condensate drain tubing for a split system air conditioning system being installed in a New York Home.

(Click photo to see an enlarged, detailed version).

Even now the drain is not perfectly sloped (note it's a bit high at that second cripple stud from left) but it was much worse before we re-routed the drain.

The air conditioner installer had the drain line sloping up-hill in the area I've circled in the photo.

Having already had condensate drain line clogs and backups and leaks from the indoor air handler into the building wall at another split-system air conditioner where the condensate drain was improperly sloped and clog-prone, I [DF] was not going to let it happen again at this installation.

The installer thought I was being unreasonably demanding.

He was ignoring the plumbing code (1/8" per foot slope for condensate drain lines) and apparently he didn't recognize the potential costs in rot, insect damage or mold if we simply let the condensate drain clog (due to an improper slope and dust that will enter the line) followed by leaks into the building wall up at the air handler.

Or this was a plumbing job "... guaranteed until my truck reaches the end of your driveway".

See SPLIT SYSTEM AIR CONDITIONERS & HEAT PUMPS for complete information about the installation, routing, insulation, & protection of condensate drains for split system cooling or heat pump units.

Air Conditioning or Heat Pump Condensate Drains Connected to a Building Plumbing Vent Pipe?

Sewer Gas & Bacterial Hazards at Air Conditioners

[Example air conditioning system inspection report language]:

Watch out: 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.

See Legionella BACTERIA & HVAC EQUIPMENT.

Below 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.

Watch out: HEALTH NOTE: Condensate drains should not be connected directly to a house drain (without an air gap) 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.

Reader Comment: traced sewer gas odors to HVAC condensate drain connection to vent stack

We just found the source of our septic smell in the East Wing of our home. It appears that the HVAC contractors who installed the system on this wing plumbed the drip line from the air handler into the vent stack without using a P trap.

That might have eliminated the problem, but I doubt it would be code compliant.

The way we found the problem was by using a smoke bomb in a shop vac and blowing the smoke down the vent stack from the roof.

While doing that, we looked for smoke in the walls where the stacks were and then looked in the attic. When we opened the access to the attic, we could smell the smoke (Superior #2B - 8,000 cu. ft. smoke bomb) and could see the smoke billowing out of the seams of the air handler. I hope this helps someone else out there --- Tom 22 May 2015 T. W. Straub

Editor's comment: It's helpful to have a "real world" report confirming what experts have been telling us for a long time and that some installers or building owners simply don't accept.

The convenient shortcut of connecting the HVAC condensate drain to the plumbing stack is overwhelming for some people even though it's a bad idea.

This comment was posted originally

at SEWAGE ODOR SOURCE LOCATION.

Also see SEPTIC / SEWER ODOR SOURCE TABLE.

A/C or Heat Pump Spillage in Building Crawl Spaces

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.

In our photo, the air handler itself was mounted in a crawl area, making service and repair more difficult and thus more costly. And spilling A/C condensate on the crawl space floor is asking for a building mold or insulation mold problem too.

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 or Heat Pump System Condensate Leaks Onto a Furnace Heat Exchanger

Air conditioner condensate leaks into a furnace as we can see in these two photographs, can be dangerous.

If the air conditioner condensate leaks cause rust holes in the furnace heat exchanger there is risk of dangerous flue gases, including carbon monoxide, leaking into the building air supply when the heater is running.

The rust seen in the bottom of the blower compartment tells us that this problem has gone on for some time.

Further inspection of the heat exchanger is needed for damage, and on most systems, further inspection for mold contamination in the air handler and duct work may also be in order since the system has been spilling water into the air handler and perhaps the ductwork.

Disposal of Air Conditioning or Heat Pump Condensate Outdoors

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.

Can A/C condensate drain onto the ground surface?

In an industrial installation, can the condensate line drain to the wastelands. Is there a code that says it must drain to sanitary?

"Wastelands" refers to Acres of grassy area at our property. 2018/05/10 Joe

This Q&A were posted originally at CONDENSATE DRAINS, CODES

Answer: it depends. Codes such as the UMC are "tricky" in their treatment of this question.

Anon:

The answer is: ... it depends. Clean, pure distilled condensate can be discharged (according to the example municipal guidelines we cite below) but NOT A/C condensate that is contaminated by cleaning agents or other substances.

According to the model plumbing codes and mechanical codes such as the UMC sections UMC 309, UMC 815.2.2, and UMC 1105.10, condensate from an air conditioning or heat pump system can be discharged to "... other points of discharge acceptable to the municipal authority."

Here is a typical guideline for disposal of air conditioning or heat pump condensate from a commercial facility.

2. Condensate from commercial & industrial air conditioning units must terminate in the following order:

i. To a landscaped area or landscape-based stormwater treatment system (e.g. bio-retention unit) that is properly-designed to accommodate the volume of condensate;

or

ii. To the sanitary sewer indirectly.

Discharges to sanitary sewer system shall be subject to all wastewater permitting requirements and fees – contact the Environmental Services Department;

or

iii. If the two discharge options described above are not feasible,

as determined by the authority having jurisdiction, then these discharges may indirectly enter the storm drain system.

Source: BULLETIN #256 02/10/16, Condensate Disposal Requirements [PDF] San José Permit Center, San José City Hall, 200 E. Santa Clara St., San José, CA 95113
408-535-3555 www.sanjoseca.gov/building retrieved 2018/05/11, original source: www.sanjoseca.gov/DocumentCenter/View/53974

Also available at InspectApedia.com at inspectapedia.com/aircond/AC-Condensate-Disposal-Guide-San-Jose-CA.pdf

The reason we don't connect condensate discharge piping *directly* or hard-piped to a sewer or storm drain (nor directly into a plumbing system vent pipe) is risk of explosive or unsanitary sewer gases being drawn into the building's HVAC system. That's why air gaps and traps are required for such connections, making the connection "indirect".

Watch out: you absolutely must check with your local building or plumbing code enforcement officials about your HVACR condensate disposal plan as municipalities vary in what they permit.

In that discussion it is essential to be perfectly clear and honest about exactly what is in your condensate drainage. For example, does the condensate contain biocides, chemicals, treatments that may not be properly discharged into the environment. Knoxville's guidelines address this concern:

It is allowable to discharge condensated water, which is essentially pure water from the atmosphere.

It is illegal to discharge any water that contains chemicals, detergents, algae-killing agents and other manmade substances onto the ground or onto any surface which drains to the city stormwater drainage system, ditches, swales, curbs, natural creeks and streams or wetlands.

It is illegal to discharge any substance (liquid or solid) to the environment in any manner that could allow the substance to wash into the municipal stormwater drainage system, ditches, swales, natural streams and creeks, wetlands or sinkholes.

This prohibition is mandated by federal and state regulations, and also included in the Stormwater and Street Ordinance (Chapter 22.5 of the City Code).

The City of Knoxville is required to prohibit non-stormwater discharge as part of the National Pollutant Discharge Elimination System (NPDES) permit issued to the City of Knoxville by the state of Tennessee.

The City Engineering Department website contains the current ordinance and NPDES permits. See IC-01 (Non-Stormwater Discharges to Storm Drains) for a list of exempted discharges.

Both air conditioning condensate and refrigeration condensate are on the list of allowable discharges, provided that such water is distilled pure water taken from the atmosphere.

However, any cleaning water or washwater can not be discharged to the ground, but must be captured for disposal in the sanitary sewer system. 

Source: IC-12 Air Conditioners & Refrigeration, [PDF] City of Knoxville TN Engineering Department (2003) retrieved 2018/05/11 original source: www.knoxvilletn.gov/UserFiles/Servers/Server_109478/File/Engineering/BMPManual/IC-12.pdf

Does AC Condensate cause roots to grow and harm the foundation?

Our reader asked:

My HVAC condensation pipe drains beside the foundation. It is less than 3 years old. I’m attaching image of the roots induced by the drain being placed beside the foundation of the house. It has undermined the foundation of the house. Is this a “code acceptable instillation? - On 2021-09-22 by Joseph Mann

Answer by inspectapedia.com.moderator - A/C condensate dumped outdoors would not, alone, cause problematic root growth at a building foundation wall

@Joseph Mann,

Thank you for the interesting photo and condensate disposal question.

It's entirely common to dump A/C condensate onto the soil next to a building so long as it doesn't spill across a public walkway nor re-enter the building through the foundation wall.

It's surprising to see so much condensate draining in a location that it would attract roots from distant plants sufficient to cause root damage to a foundation, and more-so to see a 2" diameter root against a foundation that's just three years old.

What plants are growing near the building? Size, age, species. My photo shows a tree too close to a building: a condition likely to cause foundation damage. But small fine roots are less of a concern .

How far are your roots from the building wall?

Is this a building on slab, on crawl space, or over a basement?

If either of the latter two, what can we see from inside that space?

What's the volume of condensate being drained here? From how-big a building, in what climate?

Before fixing the problem by routing condensate to a more-distant disposal point, let's be darn sure we've correctly identified the cause of the root problem.

And let's see that the actual root size and quantity are really risking foundation damage.

See VINES & SHRUBS on BUILDING WALLS, CHIMNEYS 

and TREES & SHRUBS, TRIM OFF BUILDING

Air Conditioning or Heat Pump Condensate Drains Routed to Hidden Locations

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.)

Is it OK if a condensate drain is piped into an insulated wall cavity?

An InspectApedia Reader Asked:

I’m living in a brand new home that was completed in August 2020.

I noticed moisture coming from between the framing and foundation at a spot in my finished garage and a plumber I brought in found that the condensate drain line from my furnace was piped down to the crawl space and ended within the insulation.

I’m upset that this is happening in my brand new home, though I’m glad I caught it. I’d like to know what I should ask the builder to do to remedy this, as I can’t imagine that a short pipe pointing to the crawl space, but ending in the insulation is how it’s supposed to be. The wood is already degrading :( Sincerely, Frustrated in Seattle

Reply: NO. Dumping condensate into a building cavity risks costly mold damage, insect attack, rot

Sincerely, a condensate needs to connect to a drain or to the building exterior.

Dumping condensate into a wall, ceiling, or floor cavity wets the insulation, framing, drywall or other building materials, inviting costly and potentially dangerous mold contamination as well as inviting rot and insect damage to the structure.

Is it OK to drain HVAC condensate into an open sewer pipe?

Short answer: No, not if sewer gases can re-enter the drain system and through it the building's air handler or HVAC equipment.

Above and below our photos, courtesy of InspectApedia reader MD, show multiple drains spilling into an open sewer pipe in the building floor. With no trap at the drain itself nothing prevents sewer gases from moving back up into the building or into its HVAC systems.

The building in which these photos were taken is three stories high with 8 units on each floor. The floor plans reflect the unit above and below.

Each units' A/C condensation has a PVC drip line that connects it to the unit below.

On the first floor, the upper-units' and bottom floor units all come together and drip into an opening in the floor into a raw sewage line, what appears to be a 3-inch section of pvc that is flush to the floor but wide open.

Our reader commented:

These are brand new apartments but multiple units have flooded with raw sewage and we wonder if we're next.

An untrapped sewer line is unsanitary and unsafe

The photo just below, excerpted from MD's photos, shows what looks like two condensate drains and a water heater overflow pan draining into an opening in the floor.

The reason that plumbing and air conditioning codes call for a trap on the condensate line at the air handler is specifically to prevent drawing unsafe, unsanitary gases including sewer gas into the building's air duct system.

If your condensate drains are properly trapped, then the risk therefore of sewer gases being picked up out of this drain and sent into the building are small.

Watch out: nevertheless, If this is an untrapped drain and worse if it is connected to a sewer line, the risk of sewer gases (explosive and unsanitary) would make this an improper and unsafe installation.

Hazards to watch for if an HVAC condensate drain is routed improperly into a main building drain line

The "worst things" to watch for if an HVAC condensate drain is routed improperly into a sewer or septic drain line (for example without a trap or a condensate drain positioned so that sewage or sewer gases back up into the A/C or heat pump system) are sewer gases or sewage contamination of the building HVAC system.

Without proper traps and/or check valves, such connections can lead to back-contamination of the building air with sewage pathogens and methane gas, making people sick, or a condensate drain blockage entirely that shuts down the system or leaks into the building cavities causing mold contamination.

If your condensate drain line is includes a check valve (one-way valve) which would act like the original clean-out plug except to let condensate into the pipe and on to the septic tank.

To be clear, residential A/C condensate will not affect a septic system itself. The condensate volume is trivial vs wastewater volume.

Other Questionable Ways to Dispose of HVAC Condensate Drainage

AC Condensate Drains into the Bathtub - OK?

The condensate drain in my daughters apartment drains to her bathtub.

In fact hits her right between the eyes when when is soaking. Is this legal of even acceptable practice. On 2019-07-28 by Brian -

Answer: NO, don't dispose of HVAC condensate by simply dumping it directly into a plumbing fixture such as a sink or bathtub

No; A/C condensate could be unsanitary, or otherwise unsafe.

Watch out: for example the condensate system may contain Legionnaire's disease-causing bacteria.

See Legionella BACTERIA & HVAC EQUIPMENT

The condensate drain ought not be spilling into a plumbing fixture where it can come into contact with a person.

Is it OK to Dump AC Condensate into my Sump Pump that is OFF in Winter Due to Freeze Risk?

An InspectApedia reader asked:

According to the installers, my sump pump is supposed to be inactive during the winter months in MN, due to freezing temperatures. If I am dumping condensate into it, it will eventually set off the automatic pump.

I am hoping that the expression will be quicker than it takes to freeze the condensate, which would have a lower freezing point due to ph level; expression is very fast during mild temperatures.

As is, the extension to the discharge tube (outside of house) has been removed per installer's instruction for winter months. So the discharge tube sticks out only a few inches from exterior wall.

One of the arguments others have made (reddit forum) is something akin to sump pump not operational during winter months. I guess in subzero temperatures, I can keep an eye on the discharge tube to see if it has any frozen condensate blocking the opening. - On 2023-11-20 by Nia

Answer: NO, a buildup of ice can eventually block the outlet pipe

I [DF] have a lot of experience with this specific problem in northern Minnesota and I can assure you that eventually they pump outlet will freeze and potentially then block the ability of the sump pump to discharge condensate.

Even a small amount of water remaining in the end of the outlet pipe after the pump cycle stops will be enough to freeze and that accumulates over a sequence of pump cycles. The result can be a buildup of ice that eventually blocks the outlet pipe.

We have photos of that condition at this website.

Followup by Nia

@InspectApedia Publisher,

What do we do? Install heat tape suitable for pvc? Find another discharge method - I guess I could go back to the last route, which was discharged into a 5 gallon bucket for manual emptying.

It can be super dry during winter, but this autumn seemed to produce more condensate than usual. I guess I will only use the sump pump for condensate discharge when outside is above freezing.

Reply by InspectApedia Publisher - install a small condensate pump that simply lifts the condensate up to an appropriate building drain

@Nia,

An alternative method for handling condensate waste from HVAC equipment is to install a small condensate pump that simply lifts the condensate up to an appropriate building drain.

That avoids the problem of freezing at the sump pump outlet and maybe simpler than having to maintain a heat tape on the sump pump line.

Problems with draining condensate underneath the floor slab?

Our reader asked:

My condensation line for the furnace drains into the concrete floor slab. There is no outdoor drain that I can see. I have to assume that it is either draining into the house sewer system or draining directly into the ground below the concrete.

The last copy of years I have been having issues with pvc pipes of the drain being clogged and the water just spills back into the furnace and drips on the floor.

I tried some vinegar and over the counter drain cleaner but it does not solve the problem. I tried to snake the drain under the furnace but I can barely get to a inch into the pipe and I hit something hard. I can't break thru it. I stuck a metal piece down the pvc drain and it hit something hard and I can push thru it.

I tried to take pictures of the inside of the drain and posted under the furnace and have posted them. Those are the best that I can take of what inside the pipe. The vinegar and cleaner appear to be stuck in the pipe.

I guess my question is how can I determine if the issue is that the drain line is draining into the ground under the foundation. Or does it actually drain into the sewer line or suppose to but something is clogging it.

I want to just drill a hole thru the wall and run a drain line to the outside wall which is about 7 feet from the furnace. This way it would be easier to clean and hopefully solve the problem.

I attached the best picture that I could get in the limited space. I would appreciate your opinion on what appears to me to be a metal grate in a plastic pipe. I could be wrong as it might be something else. Thank you for taking my question. On 2021-10-17 by Harvey Kelly -

Answer: Generally not OK to dump A/C condensate under a slab

@Harvey Kelly,

It is indeed the case that some installers thought it would be okay to simply drain condensate underneath the floor slab.

It may go right into the soil or there may have been, at one time, a drain line that connected to a sewer line or even to a footing drain system.

In our OPINION simply dumping condensate under a floor slab is poor practice, risking future moisture problems in the building or a clogged disposal drain that causes backups and leaks into the building.

For the circumstance of blockage that you describe, it makes sense to me to abandon that drain.

You should route the condensate to the exterior and if necessary you can use a condensate pump to lift it to drain properly.

Can the acidity of air conditioning condensate be a problem in sump pump life

Reader question:

(1) Can the discharge from the heat/ac system drain directly into sump pump?

(2) Will the (assumed) high acidity of discharge corrode the sump system? My soil is clay and water is quite hard if untreated. Do those characteristics help play into neutralizing the discharge fluid?

(3) Is there danger of stale water sitting in sump pump pit affecting the hvac (ie- bacteria)? On 2023-11-08 by Nia -

Answer: probably not

@Nia,

I haven't found scholarly research that claims that the acidity of air conditioning condensate is a problem in sump pump life.

It is a concern that condensate can become a breeding ground for legionella bacteria in some conditions.

A proper sump installation includes a cover so that you're not overly concerned about a small amount of water that remains in the pit when the sump is not active.

And in regular use new incoming condensate should cause the pump to flush out the sump pit.

But certainly if that's a concern for you dumping a little dose of bleach in there when the system is not expected to be producing condensate for weeks or months at a time should be sufficient

HVACR Condensate Drain Failure Research

• Alassafi, Hassan Th, Khalid S. Al-Gahtani, Abdulmohsen S. Almohsen, and Abdullah M. Alsugair. "HVAC maintainability risks in healthcare facilities: a design optimization perspective." Facilities 42, no. 15/16 (2024): 30-52.
• Des Champs, Nicholas, H., Ph.D., P.E., Fellow ASHRAE, HVAC, CHECK VALVE ALTERNATIVE to P-TRAP for HVAC CONDENSATE [PDF] (2020) HPAC Engineering, eNewsletter, Web: hpac.com - retrieved 2022/07/23, original source: https://www.hpac.com/piping-pumping/article/21130312/time-to-reconsider-use-of-ptraps-for-condensate-removal
• Maksimavičiūtė, Reda. "Indoor climate relation to the maintenance of HVAC systems." (2022).
• Risko, James R. "An analysis of steam process heater condensate drainage options." Energy engineering 97, no. 4 (2000): 50.
• Schwartz-Narbonne, Heather, Jonathan PD Abbatt, Peter F. DeCarlo, Delphine K. Farmer, James M. Mattila, Chen Wang, D. James Donaldson, and Jeffrey A. Siegel. "Modeling the removal of water-soluble trace gases from indoor air via air conditioner condensate." Environmental Science & Technology 55, no. 16 (2021): 10987-10993.
• Thomasnet, PREVENTIVE MEASURES TO AVOID CHECK VALVE FAILURES, IN THE ESSENTIAL GUIDE TO PREVENTING CHECK VALVE FAILURE, [PDF] (2018) Thomas Engineering, - retrieved 2022/07/23, original source: https://www.thomasnet.com/insights/guide-to-preventing-check-valve-failure/
• Walker, Iain S. Best practices guide for residential HVAC Retrofits. No. LBNL-53592. Lawrence Berkeley National Lab.(LBNL), Berkeley, CA (United States), 2003.