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Gas Vent Condensation

Wildfire Member Posts: 2
Have a bit of a challenge I was wondering what could be done for it.  The layout is a newer home (~11 years old) that had originally been setup with both a gas water heater and a gas furnace using the same vent up through the garage roof.  Last year, the water heater was replaced with a hybrid electric (good incentives + some electrical work was already being done nearby) resulting in the vent for the water heater being capped off.  It should be noted that this conversion was done in winter and it was soon discovered that, without the constant flow of hot air rising from the hot water tank, that condensate was starting to trickle down the double-walled vent on cold days (below 36ºF), seeping out of any crook or cranny that it could on its way to the furnace.  This problem has only gotten worse over the past year with the originally white powdery residue now turning orange (rust-related?).  Another relevant bit of info is that this furnace is a 80.8 AFUE unit.

So what's the verdict:  is the vent toast?  A drain has already been installed at a pipe elbow to try and route off some of the condensate, but even if it captured all of it, there's still a good 20' of run between the drain and the exhaust to worry about (10' horizontal + 10' vertical).  Perhaps there's some way to tweak the operation of this Rheem Criterion II to combat the condensation problem on cold days??



  • Paul48
    Paul48 Member Posts: 4,469

    odd that you would have this problem with the furnace installed to manufacturers specification.
  • VictoriaEnergy
    VictoriaEnergy Member Posts: 126
    Yes, it's toast

    The B vent has to be replaced.  B vents have aluminum on the inside that corroded to make the white dust, now the exhaust is corroding away the outer jacket. 

    This vent has failed and needs to be taken out of service immediately.  The corrosion will be worse in your attic where the vent was colder, there is risk it could fall apart and start venting the exhaust into your attic instead of outside.

    Bvents are only expected to tolerate very brief wet times, unfortunately a lot of furnaces with no draft hoods and designs with very little excess air will have exhaust that is completely saturated with water.  So the sweat fiercely and for long times which kills the vent.  When it's replaced the new vent should be the minimum size allowed per the venting tables, the connector  should be B vent as well, and, if allowed in your area, the length in the un-heated attic should be insulated.

    The irony is; if you looked at the economics, replacing the furnace with a 96% unit would have likely saved you a lot more money and netted you a better return on your investment than the HWH.  

    Home Owners Please Note:

    You are receiving advice from some very skilled pros completely free of charge. One of the reasons I participate is to sharpen my own troubleshooting skills. So; did we get it right? I would be grateful if you extend this courtesy back by posting the final outcome of the issue you are inquiring about. Thanks
  • Wildfire
    Wildfire Member Posts: 2
    Thanks for the advice!

    That's what I was afraid of..  Though the home was "custom built" in 2000, it was not custom built for us; believe me, there are several things (including the furnace!) that we would have gladly paid more for at the time of construction if we could have had a say.

    Instead of paying to replace the vent, we might just remedy the root cause and pay to have a 90 or 95 AFUE furnace installed with the associated exhaust being routed straight out the garage wall.  We had originally thought to do this at the same time as the water heater project, but the quotes came back much higher than we anticipated so we decided to defer it until the current system showed some sign of failing.  Though not quite the failure I was expecting (I had imagined a circuit board going out), I suppose the vent pipe problem will do!

    Though a bit of a shame (as I say, the Rheem has operated flawlessly), I'm sure the old unit has some salvage value whether intact or pieced out.  We should be getting a pretty decent tax refund back in the next few weeks, so I guess I know where that's going...  As for the old vent, we'll likely have it all pulled when the roof gets replaced in another couple of years..  You guessed it, another one of those items we would have gladly paid more for.
  • Paul48
    Paul48 Member Posts: 4,469

    That's a shame.....the difference in price between 3 tab and architectural shingles is pennies.When you look at new roof, give standing seam a look.They are doing mansions with it now, and it will outlive you by a long shot.
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