Condensation coming out of flue pipe of furnace
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  1. #1
    Join Date
    Nov 2005
    Posts
    11

    Condensation coming out of flue pipe of furnace

    I had a call today where condensation was coming out of the flue pipe junction and dripping on the floor. it wasn't much water, just like it was sweating. The system was replaced in 2003 with a lennox G60 series furnace and a HS26 series lennox 3.5 ton unit. I took of the bottom lid of the flue junction and it was rusted out from the water. I followed flue to attic thinking rain was getting in but we haven't really had rain this summer. It actually produced a small puddle on top of th furnace by flue while I was there. It was dripping in furnace on burner assembly and has been. I noticed that the storm windows were on windows and a lot of condensation was build up between windows. There was a dehumidifer hooked up to a drain . I took cap off of condensate drain and it was bone dry. Today was a 95 f about 44% humidity day with the heat index of 110. I poured water through drain it drain okay. I checked the refrigerant charge after another tech before said it was fine and it had 0 f of subcooling with the txv metering device. The suction pressure was running a 42 f evap temp It was already 70 f in house upon arrival no complaints on cooling factor. I did achieve about 10 of subcooling wanted 12 but got 10 at least. Had about 18f of superheat as well It did start to produce condensation and achieved 68 f quite quickly. I'm not sure if that has anything to do with the water though. I am been doing this 2 years now and I need somebody more experienced why a flue with no heat running would sweat. thanks for reading the long post.

  2. #2
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,616
    Check for supply duct leaks, blowing air out of the house.

    You may be pulling air down the chimney.
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    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  3. #3
    Join Date
    Apr 2007
    Posts
    6,285
    Possible leak in the heat exchanger? Was it doing the same thing last year?

  4. #4
    Join Date
    Nov 2005
    Posts
    11
    it has maintainence every year by my company but I was told that I should look at the exchanger by a ex employee but I didn't for some reason I should have though. it only has done it since two years ago maybe according to homeowner

  5. #5
    Join Date
    Apr 2007
    Posts
    6,285
    well if the heat exchanger is leaking then you would "probably" know it by the carbon monoxide detector. So in your case I think beenthere is probably closer if it's been going on for two years. There is a CO detector in the house correct?

  6. #6
    Join Date
    Nov 2005
    Posts
    11
    I'm not a 100 percent sure but we are definetly going back in sept to replace the rusted out section of flue pipe. So we can make sure their isn't a monoxide issue the pipe comes down from roof to basement and has a short stub that would normally go to a gas water heater that is capped. and then down under that a stub that goes to the furnace outlet. The short section of flue with the stubs is what rusted the bottom would be a cap. that small section was orginal but rusted due to the water condensation at some point the homeowner stuck his finger through it while we looked at it today. He swore before the new furnace in 2003 that that short stub that would normally got a water heater was open but I told him flue gasses would be in the basement his wife differs anyway they have a electric water heater instead orginal setup gas furnace electric water heater from 35 year old structure. sorry for such pointless info

  7. #7
    Join Date
    Jul 2007
    Location
    Delaware
    Posts
    3,824
    Quote Originally Posted by beenthere View Post
    Check for supply duct leaks, blowing air out of the house.

    You may be pulling air down the chimney.
    Cold conditioned air is hitting the metal flue, this will cool it down. Now you have this cool metal pipe in a high humidity area. are is condensing and running down and settling in the old water heater tie in.

    How much of the flue pipe is in the basement?
    Is their a chase for the flue that you can see go up to the roof?
    You have air leaks in the duct work.thats my take.

    Just like taking a cold soda out of the refrigerator. Set the cold can on the table and watch it sweat. The can in this case is your flue pipe.

    I'm just trying to help.

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