P-Trap question for running AC drain line across the crawlspace

Should self vent unless the drain pan gets plugged up. To help, do have a good drop/sloop. No P trap needed.

Yes it will suck air without water trap, dont do this.

It's not exactly a P-trap. He had a vent. I uploaded the pic in my post with my drawing

This is the current pic and it drains straight under the house

From what I have read it depends on where your evaporator coil is located relative to the blower, before or after, inside the air handler as to whether you have negative or positive pressure, and dictates whether or not you need a P-Trap. If the coil is under positive pressure it is not needed, if under negative pressure you should have one.

If you have paperwork on your HVAC air handler system, or can look it up on-line, the instructions on installation should tell whether or not you need a P-trap. If the system doesn’t currently have a P-Trap one would assume you don’t need one, but HVAC techs don’t always install things properly so there is that to consider.

Will a double p trap hurt too?

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Will a double p trap hurt too?

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not recommended, the potential for air getting trapped between the traps and causing what is essentially a vapor lock. If you have two traps, however, you would need to vent between the two traps, better just to avoid that if possible.

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From what I have read it depends on where your evaporator coil is located relative to the blower, before or after, inside the air handler as to whether you have negative or positive pressure, and dictates whether or not you need a P-Trap. If the coil is under positive pressure it is not needed, if under negative pressure you should have one.

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OP to add to my post above, this P Trap issue had me me curious b/c my HVAC condensate line does not have a P-trap so I did some additional reading.

If your evaporator coil in the air handler is located on the supply side of the system - meaning you have in the air handler the blower motor closest to return plenum, then the furnace/ heat exchanger, then the evaporator coil then your supply plenum, in that order, then you have a positive pressure system (return air is blown across the evaporator coil) and you do not need a P-Trap - that how my system is setup and if you have a natural gas furnace that is most likely how your system is set up but you can easily check this yourself. Techs set up system in this manner to prevent moisture from the evaporator coil from being blown across the furnace and causing it to rust.

In many areas without a gas heater in the air handler, they will place the evaporator coil in the air handler closet to the return plenum, then the air blower and then the supply plenum, in that order, that is a negative pressure system (return air is pulled across the evap coil) and those condensate lines do require a P-Trap.

As others have mentioned make sure you have sufficient slope on your extended drain line and put bleach in once or twice a clear to prevent “slime” from clogging it up.

Depending on the size of your HVAC it can easily discharge several plus gallons or more of condensate water per day during the summer so I would not discharge it into a landscape bed with plants - that’s too much water on a daily basis.

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my system is same as yours. We have a natural gas furnace.

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Then looks like you don’t need a P Trap with your condensate line extension and your photo shows you are already vented so no additional venting required. This should help with removing at least several gallon of water per day underneath your home.