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specs for trap in condensate drain?

This weekend, I removed a no longer functional electrostatic air cleaner and replaced it with an 'Air Bear' filter housing.
In the course of this work, I had to disconnect the condensate drain for the A/C coil. My brother, who was helping me, remarked that there was no trap in that drain. I immediately put that on my to do list, but it occurs to me that I need more information.
Now that the heat is on here in Western NY, I was surprised how much warm air comes out of this opening (DUH!?!)
So here's my question. The line is 3/4" copper. How big do I have to make the loop (trap) in order to prevent warm air from leaking past it in the winter and still allow it to drain in the summer when the A/C is on?
Based on the air flow coming from that, it would seem that any water that would be left in the trap after the summer season would be eventually evaporated sometime during the heating season, so my second question would be is there a way to prevent that?
I'm hoping someone out there can help me with this question.

Re: specs for trap in condensate drain?

Where does the condensate drain to? If it is into the sewer or septic system you would need the trap to prevent sewer gases from backing up into the house. If it just drains outside or or into an open drain you should not need a trap for anything.

Re: specs for trap in condensate drain?

The line from the condensate drain drains into a condensate pump that eventually drains into the sewer, but the purpose for the trap as I understand it is to prevent conditioned air from leaking through that drain line.
It comes right out of the plenum and now that I've discovered that it leaks air it, it makes perfect sense to want to prevent that air leakage (which is significant) from happening.
I could put a valve on that line and close it in the winter to prevent warm air from leaking, but in the summer when the cooling cycle is running, the purpose is to drain the condensate that's created as the A/C runs.
The summer season is when I really need a functional trap that would allow the condensate to drain, but would have enough resistance to air flow to prevent conditioned air from leaking through the drain.
If it's possible to design this trap such that it will work both in winter (when heated air will warm and eventually evaporate the trapped condensate) and summer (when the fan speed would be higher and thus the air flow leakage is greater) I'd appreciate it if someone could share the specs with me.

Re: specs for trap in condensate drain?

Dave .... you might be over thinking this.

I suspect the reason you don't have a condensate trap is likely you have an up flow or blow through type of forced air system. In other words .... the blower is located at the bottom of the furnace and the air is blown upward across the heat exchanger and A coil.

During the heating season the trap would become dry .... negating the purpose of the trap ... the reason you usually won't find a "trap" on these types of systems..... it's also a problem with the draw through types of systems.

To design a trap would require knowing the air pressure of the system.
Even if you were to successfully and correctly design the trap .... you would need to continuously keep the trap primed throughout the heating season.

A simpler method would be to disconnect the condensate line and cap it off during the heating season ..... reconnect for the cooling season.

2 cents worth.

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