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Ice Buildup on Heater Vent

Anyone know what causes this or have recommendations for how to remove it safely?

Comments

  • pecmsg
    pecmsg Member Posts: 2,023
    High Efficiency equipment produces water vapor. When it’s below freezing that’s the result. 

    Now what I don’t like is the metal. The water vapor is acidic. Can’t use meter. It should be Plastic or Stainless Steel. 

    What’s the make and model of the equipment?
    cjamesadams
  • cjamesadams
    cjamesadams Member Posts: 1
    This is from a Rheem Furnace Model RGPH-07AUER, probably around 2002. New shingle roof in 2019.
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 9,121
    May not be high efficiency. Standard units can do that if its cold enough out
    mattmia2
  • mattmia2
    mattmia2 Member Posts: 3,184
    edited February 14

    May not be high efficiency. Standard units can do that if its cold enough out

    Or if the vent is oversized so it too much mass and air for the energy left in the flue gases to heat.
  • HomerJSmith
    HomerJSmith Member Posts: 1,306
    edited February 14
    If the b-vent is passing thru a cold attic, I would insulate the b-vent in the attic, loosely with fibre glass insulation.

    The vent is normally a 4" vent, I think. One size larger if it is a common vent servicing two appliances. There are tables for this.

    The way the ice formed doesn't make sense to me.
  • cjamesadams
    cjamesadams Member Posts: 1
    What concerned me was that no other homes in the subdivision showed hardly any ice and I had just put in a new roof, making me think the stack was installed incorrectly. 
  • pecmsg
    pecmsg Member Posts: 2,023
    edited February 14
    Now that I've looked it up thats an 80+% unit so
    1) @mattmia2 Vent size needs to be checked according to the manual
    2) @HomerJSmith said Insulation may be needed in the attic.
    cjamesadams
  • motoguy128
    motoguy128 Member Posts: 351
    Do you still have a atmospheric gas water heater connected to it?

    What temperature are you keeping you house? Have you added a lot of insulation compared to your neighbors?


    I’m actually wondering if there’s a hole in the internal flue pipe and that last section of double wall is filling with water in the outside and leaking out or venting out the seam outdoors. Look like most of the condensation is coming below the flue cap not out the flue cap.

    Could there be a bird nest up inside there?
  • cjamesadams
    cjamesadams Member Posts: 1
    I do still have the atmospheric gas water heater, yes. Temps are set to about 75 degrees (normally not so high) but temps have been below freezing for 9 days. I agree with you, the placement is strange. I have noticed other neighbors with buildup, but not near as much.
  • HomerJSmith
    HomerJSmith Member Posts: 1,306
    You might have to remove the cap to see what's going on.
    cjamesadams
  • cjamesadams
    cjamesadams Member Posts: 1
    Had an HVAC technician come take a look. He confirmed a couple things. I have 80% efficiency furnace. I need a longer exhaust pipe, the shortness is causing the condensation to simply freeze (we already knew that part) but he said the pipe was to short for the ridge pitch. Thanks all! Cost me $173 to find out what you fine gents already told me. :cry: But glad to have the piece of mind it isn't something more serious. The cap was still exhausting steam and not totally sealed over. Oh, and he was adamant, that because of the 80% efficiency, that I definitely don't need to install insulation in the attic.
  • HomerJSmith
    HomerJSmith Member Posts: 1,306
    At 80-84%, you are putting a lot of heat up the stack. I'm more concerned about draft when the stack is less than 10'. I don't understand why shortness of the stack would increase the freezing of the water vapour in exhaust gases. Exhaust gases have stored heat energy which keeps the water vapour as vapour and is carried up the stack by the buoyancy of the heated gases. Heat energy travels in a straight line to what ever is coldest, up down sideways, doesn't matter. As the gasses travel up the stack, the gasses are losing heat energy to the walls of the B-vent. When the temperature of the gasses drops below the dew point, water vapour contained in the gasses condenses to a liquid. This is apparently what is freezing on your vent.

    Your cap looks to me to be a Duravent cap. The height of the vent above the roof line is dependent on the cap certification. Caps designated "wind" caps, which is stamped on the cap, have a lower height requirement above the roof line. Normally the vent terminates 2' above any obstruction 10' from the vent.

    It isn't steam as steam is invisible. It is condensed water vapour you're seeing. It's the condensed water vapour that is freezing on your stack.

    Normally, humidity drops as the ambient temperature drops as the colder air has less ability to hold water vapour. If the furnace is in a basement with a clothes washer-dryer or something that can add water vapour to the air that the furnace is using for combustion then the gasses moving up the stack will have a greater concentration of water vapour and condense out when the flue gasses meet the cold atmosphere.
    cjamesadams
  • Bob Harper
    Bob Harper Member Posts: 870
    If that roof is 6/12 or less, only needs to be 12" above roof. Inspect B-vent internally for damage/ corrosion/ penetrations. Inspect in attic for condensation, offsets, screws penetrating it, long offsets.
    Need to run combustion analysis badly. If underfired, will have weak draft and increased condensation. You can also measure the flue gas outlet stack temp. to see if approaching dewpoint. Consider adding a post-purge timer 2-4 min. It will flush out flue gases at end of each cycle.
    Turn up water temp. on WH. May have to consider drilling out/ replacing pilot orifice for higher BTU loss up stack. May have to change program on setback thermostat to maintain stack temps. Check for negative pressure in Combustion Appliance Zone for draft interference.
    A tall stack will tend to add a little draft but when exposed to outdoors it cools the stack possibly negating any gains.
    The aluminum liner in B-vent absorbs 3x the energy of the stainless steel liner in L vent. Consider switching if the B-vent is bad.
    You can add a double acting barometric damper with a spill switch to provide some dilution air.
    Unit probably under-firing.
    HTH
    cjamesadamskcopp
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