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Robert, HVACR Educator
Category: HVAC
Satisfied Customers: 161
Experience:  Licensed Mechanical Contractor, 30 years experience, 20 years teaching experience
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What is the green liquid draining from my furnace?

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What is the green liquid draining from my furnace? It drains from a PVC pipe into the sump. This PVC pipe does not come from the humidifier. The liquid has stained the side of the furnace and will not rub off. I am assuming this liquid that is draining is supposed to be green.
I can assure you that any liquid drain from your furnace unless it has antifreeze in it should not be green and should be checked
Customer: replied 8 years ago.

What is the green liquid? It's draining from both furnaces into each separate PVC pipe. It is clear that the PVC pipe is for drainage. Is it clear (condensate?) to start with, and then turns green?

We have lived in this home for only 2 years and have not signed a maintenance agreement with anyone. We don't have a good referral yet and do not trust the phone book or Angie's List. So, I'd like to understand the green liquid for myself, before someone tells me I need to replace my furnace.

If it is not gylcol solution and it coming out clear and then turning green it must be algae. Can the hose that turns green have light pass thru it

Customer: replied 8 years ago.
It's not algae. The color is sort of bright blue/green or seafoam green, and will not rub off on my hands. And, there is no smell to it. It is dry and hardened to the furnace surface like paint, so it hasn't drained in a while.

Can you tell me what kind of furnace you have?

Customer: replied 8 years ago.

I have 2 furnaces and they are both Heil, DC90, ultra high efficiency, probably put in in 1989 when the house was built. Its possible the green fluid is coming from the AC portion of the furnace. It appears there is essentially 3 parts to our furnace, it least visually. The top portion is a vent where the humidifier is attached, then there is an smaller aluminum box below this where there are rubber insulated pipes attached and a PVC pipe (that drains the green fluid) below the insulated pipes, and then there is the bigger portion of the HVAC at the bottom that appears to be the furnace. So, in essence: humidifier, AC, furnace, from top to bottom.

Yes, That is called the evaporator coil. There should be a drain pipe and two other pipes one larger than the other connected to it. In one of your previous posts you mentioned it was dried onto the furnace, where in relationship to the evaporator coil is it on the furnace.

I suspect the blue green residue you are describing is from the copper coils that make up the evaporator coil. The copper is oxidizing and the resulting (powder) is getting into the condensate (Water that has collected on the outside of the cold coil during operation). Most likely it is not going to be an issue but you should inspect the coil or have someone do it.

I have seen this condition when the condensate is slightly acidic and the copper surfaces break down.

Robert, HVACR Educator
Category: HVAC
Satisfied Customers: 161
Experience: Licensed Mechanical Contractor, 30 years experience, 20 years teaching experience
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Customer: replied 8 years ago.

That makes sense to me. Thanks