Not Having a Condensate Trap is Like Leaving a Window Open With the AC On

It’s hot. Some parts of the country are reaching record-breaking temperatures right now. Everyone is trying to stay cool, but many people overlook making simple improvements to their HVAC system. One thing we encounter during many of our inspections is HVAC systems missing traps. A missing condensate trap is like leaving a window open with the AC on. So, what is a condensate trap, and are condensate traps required?

What is a condensate drain trap?

A condensate drain trap is similar to the p-trap under your sinksThe traps under your sinks fill with water to stop sewer gasses from escaping the sewer and into your home. A condensate trap’s function or purpose depends on whether the coil is under positive or negative pressure. If it’s under positive pressure (most common), it stops your conditioned air from being blown outside. If it is under negative pressure, it prevents the condensation from pooling in your air handler, which can eventually leak and cause a mess.

Are condensate drain traps required? 

No code explicitly requires a condensate trap. However, IRC 1401.1 (we use the IRC here in Virginia) requires that “heating and cooling equipment and appliances get installed in accordance with the manufacturer’s instructions and the requirements of this code.” You will be hard-pressed to find an AC installation manual that does not require condensate drain traps. Below is a diagram from a Carrier AC installation manual as an example. Notice that it requires that both drain lines be trapped.

are condensate drain traps required

Do I/you need a condensate drain trap if you have a condensate pump?

Yes. You need a condensate drain trap even if you have a condensate pump. Remember that the purpose of the condensate drain trap is usually to stop conditioned air from being blown outside. The same logic applies if you have a condensate pump, except that without a trap, you will blow conditioned air into the pump, usually in the crawlspace, basement, or attic. The thermal imaging video at the end of this blow demonstrates this incredibly well.

What Should I/you do if my condensate drain line clogs?

Condensate drain lines regularly get clogged. On a properly installed system, a clogged drain shuts off the system or diverts condensation to a secondary drain.   The secondary drain is often a short pipe protruding from your soffit. You should know where your secondary drain discharges so you’ll know when the primary is clogged.  Here is what to do if it clogs.


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