There are two reasons why the condensate drain from an air handler in the attic should not termate into a vent pipe nearby:

1. It’s not allowed by the building code (Residential Edition of Florida Building code P3101.3 and similar in International Building Code).
2. The blower in the air handler creates suction that can sometimes suck the water out of the trap and, even if that doesn’t happen, during the winter when the system is in heating mode, the trap will dry out anyway. This will allow sewer gas from the vent pipe to be pulled into the air flow at the air handler and be circulated throught the duct system in the home.

    We saw the example shown above of a condensate drain into a nearby vent pipe recently in an empty house in Gainesville. It had been on the market for a while and, as soon as we tested the plumbing and ran the a/c, a sewer smell filled the house. So just don’t do it.

    Also, see our blog posts Can an air conditioning condensate drain pipe connect to a sink drain? and Does code require a p-trap in an a/c condensate drain? and When is an auxiliary drain pan required under an air conditioner indoor unit (air handler)? and Should I move my air conditioner into the attic?

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  To learn more about heating and air conditioning systems, see these other blog posts:

• How can I find out the SEER of my air conditioner? 

• My air conditioner won't turn on. What's wrong? 

• How can I find out the size of my air conditioner? 

• How can I find out the age of my air conditioner or furnace?

• How can I tell whether the condenser (outdoor unit) is an air conditioner or heat pump? 

• Where is the air filter for my central air conditioner and furnace? I can’t find it? 

• Does an old air conditioner use more electricity as it ages? 

• How did homes stay cool in Florida before air conditioning? 

• What is wrong with an air conditioner when the air flow out of the vents is low?

• Why has the thermostat screen gone blank? 

• Why does it take so long to cool a house when an air conditioner has been off for a while? 

• Why is my air conditioner not cooling enough? 

• What are the most common problems with wall/window air conditioners?  

• Will closing doors reduce my heating and cooling costs? 

     Visit our HEATING AND AIR CONDITIONING page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.