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AIR CONDITIONING & HEAT PUMP SYSTEMS
A/C - HEAT PUMP CONTROLS & SWITCHES
AIR CONDITIONER COMPONENT PARTS
AIR CONDITIONER TYPES, ENERGY SOURCES
AIR FILTER EFFICIENCY
AIR FILTERS, FIBERGLASS PARTICLES
AIR FLOW MEASUREMENT CFM
APPLIANCE DIAGNOSIS & REPAIR
APPLIANCE EFFICIENCY RATINGS
BLOWER DOORS & AIR INFILTRATION
BLOWER FAN CONTINUOUS OPERATION
BLOWER FAN OPERATION & TESTING
BOOKSTORE - Air Conditioning "How To" Books
CAPACITORS for HARD STARTING MOTORS
CLEANING & Legionella BACTERIA
CHINESE DRYWALL HAZARDS
CONDENSATION or SWEATING PIPES, TANKS
DEFINITION of HEATING & COOLING TERMS
DEW POINT CALCULATION for WALLS
DEW POINT TABLE - CONDENSATION POINT GUIDE
DIAGNOSTIC GUIDES A/C / HEAT PUMP
DIAGNOSE & FIX HEATING PROBLEMS-BOILER
DIAGNOSE & FIX HEATING PROBLEMS-FURNACE
DUCTS - Asbestos
DUCT INSULATION, Asbestos Paper
DUCT INSULATION for SOUNDPROOFING
DUCT SYSTEM & DUCT DEFECTS
DUCT SYSTEM NOISES
DUCTS, Asbestos Transite Pipe
DUST, HVAC CONTAMINATION STUDY
ELECTRIC MOTOR OVERLOAD RESET SWITCH
EVAPORATIVE COOLING SYSTEMS
FAN LIMIT SWITCH
FAN NOISES, HVAC
GAS EXPOSURE EFFECTS, TOXIC
GAS DETECTION INSTRUMENTS
HEAT LOSS (or GAIN) in buildings
HEAT LOSS (or GAIN) INDICATORS
HEAT LOSS R U & K VALUE CALCULATION
HEATING SMALL LOADS
INSPECTION CHECKLIST - OUTDOOR UNIT
INSPECTION LIMITATIONS, A/C SYSTEMS
LEED GREEN BUILDING CERTIFICATION
LOST COOLING CAPACITY
LOW VOLTAGE TRANSFORMER TEST
MOTOR OVERLOAD RESET SWITCH
MOLD in AIR HANDLERS & DUCT WORK
OPERATING COST, AIR CONDITIONER
OPERATING DEFECTS, AIR CONDITIONING
REPAIR GUIDES A/C / HEAT PUMP
REPAIR & DIAGNOSTIC FAQs for A/C
THERMOSTATS, HEATING / COOLING
THERMOSTATIC EXPANSION VALVES
WATER COOLED AIR CONDITIONERS
WINDOW / WALL AIR CONDITIONERS
WINDOW / WALL A/C SUPPORTS
A/C condensate drains & pumps: codes, installation, leaks, clogs, connections, troubleshooting & repair: this air conditioning repair article discusses the inspection and repair or un-clogging of air conditioning condensate systems, including Air Conditioning condensate drains, condensate pumps, and their proper installation as part of our review of condensate piping, traps, drains, condensate pumps, and the detection and hazards of air conditioning system condensate leaks in buildings.
Condensate leak health and safety concerns are reviewed.
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Carson Dunlop's sketch (left) shows the proper locations for disposal of air conditioner or heat pump condensate.
[Click to enlarge any image]
Notice that one of the most common condensate disposal locations, connection to a plumbing stack vent pipe, is not recommended and is prohibited by building code in some jurisdictions.
Uniform Mechanical Code Section 310.0, 310.1 Condensate Disposal
Here is an excerpt from the Uniform Mechanical Code pertaining to the disposal of air conditioning condensate:
Condensate from air washers, air cooling coils, fuel-burning condensing appliances, the overflow from evaporative coolers and similar water supplied equipment or similar air conditioning equipment shall be collected and discharged to an approved plumbing fixture or disposal area.
If discharged into the drainage system equipment shall drain by means of an indirect waste pipe.
The waste pipe shall have a slope of not less than 1/8 inch per foot (10.5 mm/m) or one percent slope and shall be of approved corrosion-resistant material not smaller than the outlet size as required in either Section 310.3 or 310.4 below for air-cooling coils or condensing fuel-burning appliances, respectively.
Condensate or waste water shall not drain over a public way.
To clarify, an indirect waste pipe is something that is upstream of a trap. That means we cannot dump into anything downstream of a trap. That would include the main plumbing vent stack. -- [Thanks to Al Carson, Carson Dunlop Associates, Toronto]
ICC Model Building Code, Section 307: Condensate Disposal Regulations & Recommendations
The following HVACR condensate disposal recommendations summary cites, paraphrases, & comments on the widely adopted 2006 ICC model building code section on condensate disposal, section 307 
1. Requirement for a drainage system
For the two Types of Condensate: Fuel burning devices vs Evaporators & cooling coils
2. Types, sizes, slope of Condensate Drain Piping
4. Acceptable Condensate Drainage Terminations
5. Requirements for a Backup Condensate Drain System & Backup Condensate Drain Options
6. Other requirements for a condensate water-level monitoring device
7. Model building code requirements for a trap on the HVACR condensate drain system
Condensate Pan, Overflow Pan or Base Pan Cleaning Recommendations
We did not find cleaning requirements for condensate drip trays cited in the model building codes surveyed to date. However a read of manufacturer's installation instructions can provide further advice. For example:
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). Photo courtesy Galow Homes.
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 was not going to let it happen again at this installation.
The installer thought I was being unreasonably demanding. But then, he was ignoring the plumbing code (1/8" per foot slope for condensate drain lines) and apparently 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.
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.
CONDENSATE DRAINS - Air Conditioning or Heat Pump Condensate Drains Connected to a Building Plumbing Vent Pipe?
[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.
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.
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.
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.
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.
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.
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.
Continue reading at CONDENSATE DRAIN CLEAN & DE-CLOG or select a topic from the More Reading links shown below.
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Frequently Asked Questions (FAQs)
Question: questions why it's not advisable to pump condensate into a sewer drain
(Mar 16, 2014) Anonymous said:
why would a condensate pump line into a drain be a problem when the pump has a check valve which allows no back leakage of gas or water and if the drain ever clogged, it would back up either way anyhow
Interesting question Anon. A great many, possibly more than half HVAC condensate drains do not involve a condensate pump nor any check valves, just gravity operated drains.
I'll be interested to know more about the condensate pump check valve to which you refer and if they are universally present in condensate pump systems and if they are considered adequate to prevent back contamination by both dangerous methane gases and by bacteria who don't have much respect for mechanical devices.
A quick check shows that the Little Giant condensate pump is available with an *optional* extra part - the CV-10 check valve that can be added to the condensate pump itself - it's not an integral part of the condensate pump. The Little Giant VCMX-20ULST does include a check valve. The Little Giant VCMA Series can accept the add-on check valve provided by the company. So based on just a quick review, it would be incorrect to assume that a check valve is always present and even if present, that it's rated for sanitary concerns.
Question: ok to drain condensate into the roof guttter?
(Mar 23, 2014) Anonymous said:
Is it okay to have the condensation pipe running into the guttering ?
That's a common practice; whether or not it's ok depends on where the condensate ends-up. If it's running down a foundation wall into a basement or pooling where kids might play in unsanitary water that'd be a concern. If condensate is going to be produced and disposed-of in freezing conditions that may also be a concern. Otherwise, probably fine.
Question: OK to drain condensate into a DWV tub vent?
(May 4, 2014) peanut737 said:
if you run a condensate drainline to a dwv tub vent thats venting to the roof would it be safe to say thats its ok as long as there is a breather T and running trap at the a-coil right off the condensate drain. And what if you also put 1 1/2 trap right before going into the vent.
My OPINION is that while the volume of HVAC condensate water running down a dry vent is unlikely to cause improper drain performance, in general plumbing codes don't want us to discharge water into a "dry" plumbing vent design.
I surmise you are proposing an air intake that would prevent negative pressure in the air handler from drawing sewer gases back up the condensate drain into the duct system. That sounds to me like someone inventing a solution to a possible problem (sewer gas induction into building air), and it might be a good idea. But we ought to either research to find that such a solution has already been designed and tested and approved, or we ought to propose that invention and invite expert testing.
I suspect that the occurrence of unsafe back-drafting of sewer gas into the air handler is rare, but that it has occurred enough to raise industry and plumbing code concerns. We might be looking at an uncommon event that we still avoid because should it occur the consequences could be serious.
Traps and vents and air movement that can siphon the trap can subvert its function - that is cause it to run dry and not work as a trap.
Question: sorting out mysteries of a clogged condensate drain line
(July 7, 2014) mtarnett1983 said:
We bought a house over a month ago. About 2 weeks in, I noticed a bad smell coming from the duct system. Then I heard dripping, when I pulled the vents down, I found about an inch of water on the bottom of the floor under the air handler. I wet vacked it and cleaned it up. We then cleaned the coils, wet vacked the primary drain line several times and also poured a water/bleach solution through it. We had to have Freon added to the a/c. Been cooling fine, but have noticed in the past week, the primary drain running from the air handler to outside of house is not draining any water outside. Three days ago, I found water coming down the edge of the foundation and brick, below the condensate line outside. We poured water again through the primary drain from the air handler to the outside and it flowed through just fine, but no water will come out that drain from the condensation.
Today, I wet vacked again from the outside and pulled about 3 gallons of water out. Does anyone have any idea why you can pour water through the line and it flows outside with no problem, but the air conditioning when producing condensation, will not flow through the line but instead, pool at the bottom of the concrete slab of our home below the drain line? Any help would be soooo appreciated!
This is also a gravity fed primary condensate line, it does not have a condensate pump.
One other thing, it does have a secondary line, however, when I found the water pooled below the air handler, it did not flow into the safety switch box, it was all around it. We assume that was from how dirty the coils were. We checked the P-trap and drain pan and did not find any holes in it.
The condensate must not be entering the drain line, right?
Right. When we pour water at the top of the drain line inside by the air handler, it flows right on through to the outside of the house. However, when the a/c is running, as of a week ago, nothing is dripping outside of the drain line and water is coming out of the bottom of our concrete slab foundation. We just wet vacked the drain line outside again and got about 6 gallons of water.
The water coming out by the foundation is just below the primary drain line outside.
Since cleaning it a couple of weeks ago, it was dripping outside just fine. It stopped after we cleaned it one more time about a week ago.
Is the condensate pan sloped so that water enters the drain?
Yes. We actually poured water in the pan and it flowed into the hole just fine.
You can also tell that the pan is at a higher point inside the house than where the drain on the outside is. The primary drain flowing outside is about 12" from the ground and the primary drain at the air handler is about 3 feet above the ground. I don't understand why all of a sudden it stopped dripping outside. It was dripping just fine.
My husband also took a string and held it above the primary line under the air handler, I then took the wet vac and went outside and was able to suction the string all the way through to the outside. He said he wanted to try that to see if there was a break in the pvc from the air handler to the outside
I have on occasion seen droops, loops and sags in flexible condensate drain line installations, particularly in split-system AC installations where the drain runs through ceilings or walls. I had to open a wall and straighten such a line to keep it draining as the loop low points accumulated clogging debris.
This one isn't a flexible drain line though. It is pvc from the air handler to the outside. Maybe a 1" pipe with 3/4" opening? We have a concrete slab. I would assume the pvc is running just above the concrete slab through the house to the outside? Would it be a bad idea to run a flexible line smaller than the pvc into the drain line starting at the air handler, all the way out of the house? We were wondering if by doing so, it would drain through that line and bypass the pvc. We know when we vaccum the water from outside it flows out. Does the trap need priming? It's as if though it doesn't have enough pressure to pull it outside. When we pour water through it, it flows right through and goes outside.
Thanks Dan for any help you can provide! We are grasping at straws now.
If the pipe is unblocked (run a small snake through it entirely) and properly sloped it should be draining.
Traps don't need priming in a drain line, but it would make sense to be sure that the pan slopes to the drain, that the drain opening is not so covered with water that no air can enter the drain along with water (or it may drain poorly as will any plumbing drain), and also double check that your backup overflow drain or condensate pan switch is working lest you flood the building.
Thanks Dan. The pan is sloped ok. There's no water standing as it drains as soon as we pour water in it. Do you have any idea why it would just stop dripping? It did it after we cleaned it out the third time with a bleach/water solution. I guess what you are saying is it could have developed a leak somewhere in the drain line and gravity stops it from flowing outside and it pools just inside the wall of the house? Is that why when we pour water into the drain from the inside, it goes through to the outside fine due to it is a larger amount going through all at once?
Sure. Condensate may stop dripping under these normal conditions
-the AC has stopped running
- the AC continued to run but has successfully lowered the indoor humidity such that little condensation is occurring on the cooling coil.
Question: why so much condensate coming out of the system?
(July 8, 2014) Anonymous said:
If the AC is successfully lowering the humidity, why are we wet vaccing several gallons a day out of the drain line outside? We started wet vaccing again the other day when we noticed so much water was coming out of the bottom of the foundation by the drain outside. Every day we are vaccuming the line several times and getting a total of about 7-10 gallons. We figured it would be better to try and get as much water out of the drain that we can so it doesn't pool behind the outside wall.
Agree - I was responding to possible reasons one may not see water coming out of a condensate drain.
In most installations the condensate drain system is not complex. I'd follow the water from its initial location on the cooling coil, into the pan, from the pan to the drain, through the trap, through the condensate drain to outdoors.
The bad thing is that the drain line is either installed in the concrete slab or right above it. We would have to either tear down sheet rock to follow it or break up our slab from the bottom of the air intake and then 23 feet to the drain outside.
Anon I'm certainly not advocating tearing up a 23 ft slab - by the way the long length of this run is NEW data in this discussion and invites speculation about easily clogged insufficiently sloped condensate drainage.
Before anything so heroic I'd install a separate condensate drain pump to dispose of the condensate without relying on the problematic drain system
I appreciate the information! I will research the information about installing a drain pump. Is that a DIY or should we have a professional do that?
If you are handy and will read the instructions it's pretty easy.
If the equipment is hard to access, I'd speculate that if the condensate drain, drain pan, etc are not present, or if wiring repair is needed, then in my opinion the original AC installation was incomplete and the installer should finish the job properly.
Question: do vibrations from the air handler cause condensate drain leaks?
8/20/14 Joelzingerman@yahoo,com said:
Our drain is made of PVCpipe. It had a crack and water leaked through the ceiling. they repaired the pipe and this weekend there was another leak onto the second floor ceiling. both AC units are in the attic. a repair man came found a hole in the pipe and installed a new section of pipe. He went outside . Made a few other joints to the pipe and secured the pipes to the base on which the condensers rest. This does not seem proper to me. Wouldn't vibrations from the running AC possibly loosen the pipes somewhere where we would have further leaks. this is a newAC
I cannot say from just the information in your message what might be improper or not.
I agree that HVAC equipment vibrates.
But it is not common - that is we've not particularly had field reports indicating - to hear of condensate piping leaks from that cause. If the piping is the proper material, properly joined, routed, and supported it should be fine. Where I"ve seen failures usually they were due to failure to properly prep and glue joints or failure to properly route, slope and support the drain lines. Condensate line blockages are more common than breakage-leaks.
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