Page 1 of 2 12 LastLast
Results 1 to 13 of 22
  1. #1
    Join Date
    Jan 2006
    Posts
    12
    We have a 2-zone heating and A/C system. We are replacing the gas water heater and 1 of the 2 gas furnaces.

    The water heater will be replaced with a same capacity unit. It will not be a high efficiency unit.

    The existing 110,000BTU Lennox furnace (circa 1968) will be replaced with an 80,000 BTU 2spd. Trane 80% efficiency unit. We were told by 1 of the companies that we met with that he is 95% sure that we'll need to get a new, smaller liner for our chimney flue. He said that the exhaust from the newer, more efficient water heater and furnace could cause condensation problems and potentially damage the heat exchanger. He further said that Trane would not honor the warranty if the exchanger damage was caused by this situation.

    It makes sense, yet we're concerned that he is the ONLY person who mentioned it out of 3 Trane dealers + 1 American Standard dealer.

    Any comments are appreciated

  2. #2
    Join Date
    Jun 2000
    Location
    WYO
    Posts
    2,019
    Its correct that the furnace and water heater vent needs to be addressed.Not enough info on your part,I would go with the Contractor that addresses it.
    never say never

  3. #3
    Join Date
    Jun 2000
    Location
    WYO
    Posts
    2,019
    Its correct that the furnace and water heater vent needs to be addressed.Not enough info on your part,I would go with the Contractor that addresses it.
    never say never

  4. #4
    Join Date
    Mar 2005
    Location
    burlington county n.j.
    Posts
    9,765
    do both furnaces vent into the same chimney?? liner normaly has to be installed to protect the chimney. 80% furnace into exterior chimney will condense flue gases and eat chimney from inside out.

  5. #5
    Join Date
    May 2001
    Location
    Kansas City
    Posts
    2,729
    Would need more info. Is your chimney exposed to any outside walls below the roof line? If so you need a liner.
    If the chimney is internal below the roof we would need to know if it has a tile liner, what size the opening is, what the BTU rates are for all units. It doesn't sound like he's for sure if you need a liner but he should be, but its good he is aware you might.

  6. #6
    Join Date
    Jan 2006
    Posts
    12
    Our chimney has 2 separate flues, one for our wood burning fireplace and the other for the water heater/2 gas furnaces. I do not know the flue size. We had our fireplace flue re-lined last year with a stainless steel liner and I recall that it had been terra cotta, but I don't know if that necessarily means that the other flue is constructed the same way.

    What confuses us is how we determine whether or not we need a new liner. It is actually the utility company rep who mentioned the liner issue, but he also said that they subcontract out anything having to do with chimneys to a chimney company. I'm thinking that there has to be some kind of mathematical equation that tells us what size flue we need for the HVAC situation that we have (1 water heater & 2 furnaces **BUT** 99% of the time we're only using 1 furnace at a time) {This is where the headache begins for us homeowners... maybe it is the CO...)

    Basically, the only thing that is changing from the existing setup is that the 110,000BTU 1964 Lennox (of dubious efficiency) will be replaced by a Trane 80,000 BTU 80% efficiency unit. The gas water heater is being replaced with a same-sized (50g) unit and the other gas furnace (a 2001 Trane 80,000BTU 80% efficiency) is a constant.

    So his premise is that we need a new liner for the flue strictly because of the change from the 110,000BTU Lennox to the 80,000BTU 80% Trane.

    How would you proceed if this were your home?

  7. #7
    Join Date
    Aug 2004
    Location
    S.E. Pa
    Posts
    6,304

    Cool need liner?

    The chimney must meet the class of service. Installing the higher efficiency equipment into a cold, wet oversized flue is a recipe for condensation.

    According to NFPA, because you are changing the efficiency, a Level II inspection is indicated. This will show that the chimney indeed already has problems in addition to being oversized.

    There are some on this forum who swear that common venting a fan assisted furnace with a draft hood equipped water heater will spill CO during the pre-purge. How much is spilled is another discussion but just consider it.

    The chimney will need the liner regardless whether or not it is an interior or exterior chimney.

    When in doubt, contact a chimney professional.

  8. #8
    Join Date
    Jan 2006
    Posts
    12
    Originally posted by rsmith46
    Would need more info. Is your chimney exposed to any outside walls below the roof line? If so you need a liner.
    If the chimney is internal below the roof we would need to know if it has a tile liner, what size the opening is, what the BTU rates are for all units. It doesn't sound like he's for sure if you need a liner but he should be, but its good he is aware you might.

    Sorry, I neglected to address these points.
    Yes, the chimney is exposed to outside walls below the roof line. The utility company salesman did say that he was not sure if we needed a new liner and would arrange for their chimney inspector to check it out once we agree to buy our equipment through them.

    We're surprised that no one else so much as mentioned the drafting issue.

  9. #9
    Join Date
    May 2001
    Location
    Kansas City
    Posts
    2,729
    Yes you need a liner, if the chimney is exposed to even 1 outside wall below the roof you can't vent an 80% furnace into it.
    What happens is the flue gas is not as hot as the old furnace so the flue gas can't get out of the chimney before it cools off below dew point and condenses inside the chimney and is acidic. It will eat the mortar and the terra cotta liner.
    Most HVA/C contractors can install a flexible metal liner.

  10. #10
    Join Date
    Jan 2006
    Posts
    12

    Re: need liner?

    Originally posted by hearthman
    According to NFPA, because you are changing the efficiency, a Level II inspection is indicated. This will show that the chimney indeed already has problems in addition to being oversized.
    Just to clarify, we're not getting any "high efficiency" units (I'm thinking of the 90+ types that vent using PVC); nonetheless, we naturally assume that the 80% Trane will be more efficient than the Lennox it is replacing, though I've had several contractors tell me that it was a top of the line unit in its day.

    Point taken, however, that we should contact a chimney professional to check out the flue.

  11. #11
    Join Date
    Jan 2004
    Location
    PA
    Posts
    68,793
    If its terracota you need a liner no matter what.

    Contractor locator map

    How-to-apply-for-Professional

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

  12. #12
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,613
    Outside chimney, line it!

    http://www.johnmills.net/liner/liner.html

  13. #13
    Join Date
    Jan 2006
    Posts
    12
    That's a great link that answers my questions about sizing and the source of the rule. Never would have come across it myself. Thank you.

Page 1 of 2 12 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Comfortech Show Promo Image

Related Forums

Plumbing Talks | Contractor Magazine
Forums | Electrical Construction & Maintenance (EC&M) Magazine
Comfortech365 Virtual Event