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  1. #1
    42yrs exp is offline Professional Member BM -bad email address
    Join Date
    May 2003
    Posts
    176
    If a 90 percent heater is installed and PVC is used,what is usually done with the water heater flue. Since the heater is no longer using th Chimney doesn't that make the chimney well oversized for the water heater?

  2. #2
    Join Date
    Dec 2002
    Location
    Toledo, Ohio, United States
    Posts
    12,901
    yes and a chimney liner is installed for the W/H
    No Heat No Cool You need Action Fast

  3. #3
    Join Date
    Aug 2002
    Location
    Westlake, Ohio
    Posts
    2,470
    When the old furnace was still installed how many times did the water heater operate in that flue when the furnace wasn't running? Most of the summer for sure but I bet it cycled in the winter independently of the furnace. When the old furnace was installed but was not running how did it help the water heater? In fact the draft hood of the furnace cooled the flue gases of the water heater when it was idle and made it harder to vent. The water heater by itself should heat the chimney better without the furnace draft hood dilution. The flue is not too big if the water heater is running correctly. If it is crying it just might be lonely.
    captain CO

  4. #4
    Join Date
    Dec 2004
    Posts
    23
    I had high efficiency furnace installed recently and my natural gas water heater was left using chimney. I had chimney made out of some sort of metal. I was told that code in our area (Toronto, Canada) requires chimney to be religned. I had 6'' chimney, they came in and put lining 4''. Here it cost about 400 CA$. If you have brick chimney you might have different problem - corosion.
    I was told that in very very cold days water heater allone cannot heat chimney flue by itself to make sure that burned gas is lifted out, so some of CO can go back into house.

    Regards,

  5. #5
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    33,918
    We've found more venting & condensation problems with orphaned water heaters than anything else. The 7 times rule in the NFGC addresses sizing.

    Even had one that met the 7 times rule, inside chimney, high BTU, 4" draft hood outlet. Still wouldn't vent til a nice little 4" liner kit was installed.

  6. #6
    Join Date
    Aug 2002
    Location
    Westlake, Ohio
    Posts
    2,470
    Originally posted by vm020306
    I had high efficiency furnace installed recently and my natural gas water heater was left using chimney. I had chimney made out of some sort of metal. I was told that code in our area (Toronto, Canada) requires chimney to be religned. I had 6'' chimney, they came in and put lining 4''. Here it cost about 400 CA$. If you have brick chimney you might have different problem - corosion.
    I was told that in very very cold days water heater allone cannot heat chimney flue by itself to make sure that burned gas is lifted out, so some of CO can go back into house.

    Regards,
    So you are saying in Canada on cold days the furnace must also operate everytime the water heater is running. If not how does the furnace help the water heater vent if the furnace is not running?
    captain CO

  7. #7
    I have struggled with the same concern because our company will not orphan a water heater, without relining when installing a 90+ furnace. The reason that was explained to me is that on very cold, windy, low pressure days, the flue gases could condensate and cause the gases to back down the flue and exit through the diverter potentially causing a CO problem.

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