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HE Furnace Condensation


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What causes this much condensation to accumulate in this high efficiency furnace (see pic)? The condensate pump seems to be functioning correctly.

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Does the picture show condensation on the *outside* of the collection box?

If so, the box would have to be cold and warm, humid air would have to be present on the outside. I'd speculate that negative pressure in the furnace room was drawing outdoor air in through the plastic vent and causing the box to become chilled when the furnace wasn't running. Was the furnace in the same room with a clothes dryer or other exhaust fan?

If this is the case, and if the furnace draws its combustion air from this room - as it would have to for my theory to work - then there's a high risk of spillage when the furnace is running.

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Thanks for the replies. I should have been a bit more detailed with the installation. Furnace is located in the garage next to a water heater and draws combustion air from the garage. I have never seen a clear collection box so I was a thrown off by the amount of condensation inside. An important note is that this home has been vacant for a few months and I presume the furnace has not been run in that time. My photos were taken prior to my operating the furnace. I've attached another pic of the installation area.

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I see those all the time. One of the selling points that the salesmen like to make for these is that they extract the heat from everything, even the condensate; and I think this is the manufacturer's way of showing that to folks. As long as that condensate is inside the furnace and the drain system is functioning properly, and there isn't any leaking out of that plastic cover onto the electronics (Had one of those once), it's fine.



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  • 2 weeks later...

The clear rectangular box is the very end of the heat exchanger and meant to collect condensate from the combustion process. Some other furnace brands are black and you just don't see the condensate. If it is draining properly and the furnace is running, all is well.

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