Is it required to have a plumbing trap on a condensate line that runs to outside

Is it required to have a plumbing trap on a condensate line that runs to outside. I have inspected for 20 years and I have never seen a requirement for this to be done. Occasionally I have seen it installed.
I was asked to inspect after another inspector. And he wrote up the condensate line not having a P trap.
What code or requirement says one has to be there and if so what if there is already a internal one on the unit?

Around here it is required.

The IRC & the UMC requires one , I believe the trap depth is per manufacturers instructions.

I am not sure about code, but the need for a trap will depend on design of A/C system. Condensate comes from evaporator coil. If fan is located before the coil in the system, the fan will push small amount of air and water down condensate drain. If fan is located upstream of coil, fan will pull water up drain line counter to water flowing down drain. A P-trap is needed to block air and allow condensate to drain properly.

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What type of furnace is running to this as well. High efficiency furnaces create an acid condensate that should not be discharged to the ground.

For the most part evaporator condensate traps are required by the manufacturer help to meet the energy efficiency standards as without it air will blow through that hole. If there is a trap tell them tho clean it all the time because it’ll clog and when it does they might call you. If there is no trap…note it and tell them to still clean the line occasionally. How the condensate lines are run varies somewhat with the manufacturer…but one thing for sure…if there is a trap…it’ll need cleaning, with a brush preferably at least yearly…and always check the trap to see if it is clogged already which it will be 80% of the time…if there is no way to check to see if it’s clogged tell them to consider adding a cleanout.

Hi Larry, I believe there is a trap and vent added to the condensate drains. the vent should be beyond the trap (3 or 4" pc.) The purpose of this is it prevents whats called blow by, that’s where the unit’s air interferes with the condensate and will prevent it from draining. I saw this first hand on a commercial air handler I installed when I was in the field. I found water had filled the bottom pan completely simply because I did not pipe it correctly.

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Thanks for the explanation, Kevin. :grin:

A trap is required by the Mfg.

Is the evaporator coil up or down stream from the indoor fan?
Where does the drain discharge?
What is the static pressure of the return duct? Should never exceed 3" WC. (Per Mfg requirement).

The indoor coil sits in a shallow drain pan. If the drain is in a negative pressure it will cause the water level to rise in the pan and may flood the unit or the house. This may not be happening during the inspection but if someone doesn’t change the air filter the pressure will increase and make it happen at some other time and you’ll be the one getting a call from the buyer.

So call it out regardless.

Where in the IRC is a trap required?

UMC 310.5. I recall that it says it shall be trapped per the manufacturer’s instructions. I have to get my IRC code book back from my friend to find where it is stated but I believe it basically says the same as the UMC

Keep in mind that the ‘reason’ for the trap is not the same reason for a plumbing trap.

It affects the operation of the HVAC, not the sewer.