Air Conditioner Water Leaks

Detection, Repair, and Prevention

When your air conditioner is running, and you discover water in your basement, seeming to come from the furnace, it's not a problem that you can ignore.  If  you  have a finished basement, the water will continue to accumulate and damage your furniture as long as the air conditioner is running.  And if the water is dripping through the inside of the furnace on its way down, this is a problem that requires IMMEDIATE attention.  So, the tips on this page are formulated to help you diagnose the cause of water leakage, and perhaps even to solve your problem without the aid of a service call.


Water Standing Around the Bottom of Your Furnace

Water standing around the base of your furnace can come from a number of diverse causes.  Some of these problems can be diagnosed and rectified simply; some you can further diagnose if you’re feeling adventurous, and in other cases the water is a symptom of a greater problem that has to be solved by a trained professional.  back to top

Humidity Removal 101 - How a Central Air Conditioner Removes and Disposes of Your Home's Humidity

Some of the benefit and most of the comfort of central air conditioning comes from the removal of humidity from the air. 

When the air passes through the furnace, it goes through the evaporator coil.  The evaporator coil is sealed into the sheet metal above your furnace.  It looks somewhat like a car radiator, and it’s where your outdoor air conditioning unit delivers the cooling.  As the air is cooled, the humidity from the house air is condensed into liquid water, by the same principle which forms drops of water on the outside of an iced tea glass on a warm humid day in Summer. (mmmm – iced tea! Take a short break right now and have some iced tea – you know you want it!) 

However, the condensation in an air conditioning system is occurring on a much larger scale, and produces gallons of water, which have to be disposed of.  When everything’s working right, as it usually does if you’re having yearly maintenance performed on the air conditioner, the water collected on the coil surface drips down into a rain-gutter pan under your evaporator coil (still in the metal cabinet ABOVE your furnace).  This pan is equipped with a drain fitting, which feeds out the side of the furnace, travels through a drain hose, and exits down your floor drain. (if the floor drain is not used, the furnace is equipped with a condensate pump.

But, sometimes, the water ends up on the floor, and that’s where we don’t want it. Depending on how adventurous you feel there are a few things that the homeowner can check without any specialized tools or training, to better diagnose and perhaps solve the problem of mis-directed water.
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Diagnosing the Source of an Air Conditioner Water Leak

Take a moment, and a good strong flashlight, and see if you can tell where the water is coming from, and what route it is taking to get to the floor.  Does the water come down the side of your furnace? Does the water seem to originate from underneath the furnace?  If the source of the water leakage is not obvious, check first inside the upper cabinet of the furnace.  Remove the upper panel of the furnace, being careful not to touch any of the components inside.  

Is there an accumulation of water inside the cabinet?  It should be dry in there.  If it is not – if there is an accumulation of water, or a drip, condensation, or anything having to do with moisture inside the furnace cabinet, TURN THE FURNACE OFF before further damage occurs.  Water is the enemy of all things electronic, and if your circuit boards get wet, damage can be extensive and expensive. So, if there’s water inside the cabinet of the furnace, turn off the furnace (using the light switch on the side of the furnace, or at your home’s circuit breaker panel) and CALL OUR SERVICE DEPARTMENT. 414/778-4190.  Someone answers the phone 24 hours a day. 

If there is no immediate danger to the sensitive components inside the furnace, perhaps there is something you can remedy yourself. 
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Drain Pan Water Backup

Does the water seem to originate at the point where the bottom of the galvanized sheet metal meets up with the top of your furnace, and then run down the side of your furnace?  One cause for this could be a blockage in the hose or the drain fitting of the pan.  Try a few of the following steps, and you’ll get a better handle on what is – and isn’t – causing the water backup.  back to top

Squashed Hose

Squashed hose – boy, isn’t that embarrassing when the service technician comes out to look for a water leak, and you find that box of Home and Garden magazines parked right on top of the hose, right where you put it - squashing it down so that the water backs up!  Put them somewhere else - maybe you should build another shelf in the basement. back to top

Drain Hose Air Lock - Applied Science

Take a look at the discharge end of the hose – the end where the water is supposed to come out. Is it submerged?  That is, does it go down into the drain, and end up underwater?  Did you know that just one air bubble in the hose will prevent water from flowing out of that hose? The water that is already in the drain seals off the water trying to come down  – it’s called an Air Lock. It’s science, and it will cost you the price of a service call if you have to have a professional pick up the hose out of the water.

Be sure that the hose ends before it enters the drain (Cut it off so you can keep an eye on the end.) And make sure that the discharge end of the hose is not underwater
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Water Runs Downhill - More Science

Water Runs Downhill - The passage of the hose from the furnace to the drain should be continually downhill.  Water is not going to run uphill, even for a short distance.  We are assuming that if the hose was once working, that it was properly placed.  But if you have recently moved the hose so it takes a different route to get to the drain, you have only to look in the mirror to see who the culprit is.  If the hose tries to run the water uphill, it could form an air lock, (see above) or simply not run at all. back to top

The Ever-Popular Clogged Hose Checklist

When the home’s air passes through your furnace, sometimes it leaves behind small amounts of dust, pollen, and general household air dreck.  When the condensation from the air conditioning process passes through the hose on its way to the drain, there can be a buildup of this solid material.  Mold, mildew, and algae buildups are also possible inside the hose, and this can clog the line as well.

Some groups of symptoms point to a clogged hose. If the air conditioner is running normally but no water is coming out of the end of the hose, or if there is water coming down the side of your furnace, sometimes all that is needed is to unblock the clog from the hose.

Here are some things you might want to try on your own, perhaps to fix the entire problem, and possibly to save the cost of a service call:
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Be sure that there are no kinks in the hose impeding the water flow
checklist Once again, check the placement of the hose.  Every foot of it should be running downhill, not just the end by the drain. Water runs downhill.  Are you the one who moved the hose, and now it runs partly uphill? Well, move it BACK right now!
checklist Moving all along the route of the hose, from fitting to drain, squeeze the hose with your fingers, to loosen any accumulated debris. It’s like massaging a python, but it won’t bite
checklist If you have an air compressor, blow some compressed air into the discharge end with your air hose, and GET OUT OF THE WAY after releasing, because if you dislodge the clog, the backup will drain out of the hose very fast.
checklist The following is something we heard from homeowners  ;> but wouldn’t personally recommend, for aesthetic reasons: Grasping the discharge end of the drain hose firmly, blow into the hose, then put it quickly down onto the drain.  Personally, I’d rather be blowing on a trombone… Have some mouthwash handy if you try this one, and remember, you didn’t hear it here.
checklist Disassembly of the hose. Detaching the hose from the fittings, there are many options to explore, for instance, probing gently into the fitting with a pipe cleaner or other soft wire, replacing suspect sections of hose (we’ve got replacement hose at our parts counter, and you can also get it at some hardware stores.).  This may solve your blockage problem. back to top


Leaky Drain Hose

If there is a hole in the hose, due to age of the hose or something that was moved across the hose, puncturing it, the hose section should be replaced. When replacing hose sections, be sure to get BLACK hose, and not the clear variety.  The clear hose tends to act just like a little greenhouse, and algae thrives inside the warm, moist interior of the drain hose, causing eventual clogging. back to top

Leaky Drain Fittings or Hose Fittings

Check the fittings wherever the hose fits onto an elbow, coupler, or drain pan fitting.  The hose should be securely pushed fully onto the fittings, and there should be no water leakage evident.  If there is leakage, and the hose doesn’t seem to be the source of the water, perhaps there is a cracked fitting.  You can get new fittings at our parts counter, or at many hardware stores.  Bring the old fitting with you so that you get an exact size match. back to top

Condensation on the furnace plenum

When your air conditioner is operating, the air is cooled in the plenum space above your furnace.  That’s where the outdoor unit delivers the cooling to an evaporator coil (looks a lot like a car radiator) through which passes the air from your house.  Considering this, it is normal for the furnace plenum (the metal part above your furnace) to be cool to the touch. 

Sometimes, if there is enough moisture in the basement air, there can be condensation on the outside of the furnace, and, if there is enough accumulation, it will run down the sides of your furnace, and onto the floor. This problem is not due to the air conditioning system at all; the water is coming from the air in the basement, not from within the furnace.

This same condensation can occur on the copper pipes which lead from the furnace to the outdoor air conditioner (these are also called tubes, lines, lineset, etc – refrigeration nomenclature is not always standard.)  Water on these pipes is also from the air in the basement – there is no water inside of these tubes that can leak out, and a leak in one of these copper lines is a MAJOR problem that the homeowner can’t fix, so be careful around these copper pipes.

Condensation on the furnace is brought under control by controlling the humidity in the basement.  If your basement area is not air-conditioned, you may consider running a dehumidifier in the basement. If the air is dry, the condensation will be minimized.
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The Possibility of an Ice Block in Your Furnace Plenum

Does your air conditioning seem to be blowing out the registers with less force than usual?  This could be due to an ice block forming in the plenum of your furnace.  Follow this link for detailed instructions for diagnosing and preventing this problem.

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Air Comfort Systems, Inc.
635 South 70th Street
Milwaukee, Wisconsin 53214

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