Home Inspection Library J C Weise Property Inspector Atlanta, GA www.UpscaleInspections.com

Attic Furnace Drain Pans

        If you have a central heating and cooling system where a horizontal furnace is located in the attic, there are a few things you should do to help ensure that you don’t have any water damage when you run the cooling system.

       First, make sure that there is a drain line running from the evaporator coil to the exterior of the home or to a proper drain system. The evaporator coil is where humidity condenses after being taken out of the air during the cooling process. Anytime there is water, there is the possibility of water damage from some sort of leak. Because many people use their cooling system only a few times each year, some heating and cooling professionals will charge for the drain line but skip putting it in thinking that no one will ever miss it, and by the time they do, he’ll be long gone or the warranty will have expired.

       Second, make sure there is a drain pan under the evaporator coil. Drain pans are shown in Figure 1, Figure 2, and Figure 3, most clearly in Figure 2. The drain pan ensures that if there is a leak in the evaporator coil, any leaking water will be caught by the drain pan. Some manufacturers include an interior drain pan, but I have no way of verifying such construction since the drain pan won’t be visible. However, if an interior drain pan is present, the best heating and cooling professionals will install drain lines as shown in Figure 3. However, considering the amount of damage that can result from a water leak in the attic, I prefer a redundant drain pan installation, which is what Figure 3 shows.

       Third, make sure that there is a secondary drain line installed, usually from the drain pan. With the secondary drain line installed, if the main drain line gets clogged, condensate can still drain properly without backing up into the evaporator coil and rusting it out. The secondary drain line should terminate somewhere that is very noticeable so that if you see water draining from it, you’ll know that the main drain line is clogged and that you need to call the heating and cooling professional immediately after shutting the cooling system off. Good locations to terminate the secondary drain line are near the front entrance, near the garage, or near the back patio. In some instances, particularly in condominiums, the secondary drain line will terminate above the bathtub or shower, again so that water draining from it will be noticeable. You should never let a heating and cooling professional talk you into terminating the secondary drain line in the drain standpipe for the washer or tapped into the sink drain lines under the sink. It’s vitally important that you know that water is draining from the secondary drain line if it ever occurs.

Figure 1. Black drain pan under furnace in attic.

Figure 2. Drain pan under furnace in attic.

Figure 3. Drain pan under furnace in attic.

       And lastly, for extra peace of mind, you can have a float switch installed in the drain pan or as the secondary drain line (see Figure 4) so that if the drain pan is full of water, or if water is draining from the secondary drain line, the float switch will shut the system down.

       If you decide to get into the attic to look at your central heating and cooling system, please be very careful. The attic is a dangerous area of our homes, and there are untold stories of people falling through the ceilings or passing out from heat stroke. Don’t go into the attic if you are the only one at home; wait until someone else comes home. For more information about attics, click here.

If you have any questions about anything, simply contact me.

Figure 4. Float kill switch on furnace in attic. Note that there is not a drain pan. Float switches do fail quite often, so I prefer to have the added safety of a drain pan for attic insulations.

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