Is condensate drain necessary?

Hi, brand new inspector, love InterNACHI’s offerings!

On an inspection today, saw a 4 year old central gas furnace with evaporator coil ready to hook up but no central AC has ever been connected. Condensate drain lines were still plugged. My training always assumed the AC was connected so I believe this to be a defect; but could someone clarify if a condensate drain line is needed for just a furnace?

I’m sure this was answered, but I cannot find it. If it was answered, any advice for finding answers is also appreciated!

Marshall Tramp

Only if it’s a condensing (90+) furnace.


Why do you think the condensate drains would need to be ran?

You know the answer to this. That puddle you see under your car after a trip on a hot day is AC condensate. Same thing happens when you run the AC in a house. Moisture in the cooled air condenses at the evaporator and needs to be plumbed away from the cabinet. If the AC is not working there’s no condensate.

Heavily rusted furnace cabinet from AC condensate…

With all due respect Bob, I think you missed this part:

@srechkin has right.

Not at all. “If the AC is not working there’s no condensate.” Not working includes not hooked up. The OP says nothing about a condensing (90%) furnace.

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If the Evaporator is not active then you would not (Yet) need a condensate drain/line. At present, the evaporator drains should “Remain Plugged” to prevent heated (furnace) air from escaping or unfiltered air entering the system. They will need to be attached/installed when an AC condenser is added and put in to service for cooling (and may need a p-trap) .

The condensate drain for a high efficiency, condensing Furnace is a different matter and not the same as those at the evaporator.

(I’m guessing they installed the evaporator section now as it was anticipated to add the condenser for cooling later (maybe on a budget but forward thinking.) adding the evaporator now probably takes the guess work out of trying to fit it in later.


Sorry, I missed that:

guys asking for help, do you have a answer for him?. I have seen answers like this alot on here. people ask for help and get asked a question as to why. If you can’t help don’t answer. So Why do YOU think he needs it?.


Go easy on him, Martin :slight_smile:

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So in the 32 minutes you’ve read on the forum you don’t understand that sometimes by asking a question it may spark a thought process from the OP. Two things must be determined before there is a need for a condensate drain line. The OP has not given enough information hence my question.

You are a forum troll with nothing of value to add to this forum except for an attack.

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Because fire does create water vapor. I know it (mid efficiency furnace) isn’t comparable in amount with a high efficiency furnace or AC, but I wondered if it was enough that you all would call a missing condensate drain line a defect. I gather that no, it is not a problem; thank you all! I had no idea this would be such an interesting topic :slight_smile:

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It isn’t really missing if the A/C coil / system hasn’t been installed yet.

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I agree 100%.

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That’s the information I was looking for.

What is the efficiency rating of the furnace and has the “A” coil been installed?

Without the line set material connected to the unit and hooked up to an outdoor unit I see no reason to run the condensate drain.

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Yes but a mid efficiency exhaust flue is hot enough to prevent condensate.


That’s a fair point

Physically, yes the A coil exists inside the unit; but it does not have a compressor nor refrigerant lines going anywhere, they are stubbed out for future use (at which point it will obviously be necessary to drain condensate). I’ll make sure to include more appropriate details next time, thanks!

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Exactly. It is not considered an HVAC or Split system, it is simply a Furnace.

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