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  1. #1
    Join Date
    Mar 2004
    Location
    Central NJ
    Posts
    25

    Need to understand 95% Eff venting requirement

    I'm getting bids on a residential split system replacement with heat. I wanted to qualify for the $1500 tax incentive so he told me it's easier to hit with heating since the 16+ SEER ACs are a bigger investment and given my Northeast location, the 95% AFUE would have a shorter pay off period.

    Right now I have both the NG hot water and furnace venting into an all metal chimney (I'm guessing it's 10" diameter). I understand the 95% units use two PVC pipes, one for intake and one for exhaust. But what I thought I read around here is that the larger chimney is no longer appropriate to vent just the water heater. He just said that they'd block off the HVAC entrance in the WYE and it's fine.

    The company is 75% NATE certified but I want to be an educated customer for the next couple bids. Thanks for any help.

    Bobby (NJ)

  2. #2
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,095
    It is really 10"? Could be a venting issue if the common flue is really that big. If the inside dimension is smaller, it would be OK. Can snake a small flue liner through that big pipe to avoid condensation too.

  3. #3
    Join Date
    Mar 2004
    Location
    Central NJ
    Posts
    25
    I guess I should measure it. It goes up through a 2x4 framed chase until it gets to my attic. The exterior dimension as it pokes through the roof certainly looks to be 10-12" but are these usually double walled?

  4. #4
    Join Date
    Feb 2007
    Posts
    999
    Bobby: Here is a link to the NJ building codes. You'll have to search for the section.

    http://www2.iccsafe.org/states/newjersey/

    I had my furnace replaced and the issue of a liner was discussed.

    The code spells out acceptable situations which take into consideration the heat input of the water heater, and the diameters of the water heater flue to the (old) furnace flue.

    I did not have a liner installed, but tested it with furnace on/off with WH pilot only running. No back drafting.

    Amp

  5. #5
    Join Date
    Jul 2000
    Location
    Northern Wisconsin
    Posts
    2,006
    Leaving a water heater connected to a chimney that was used to serve it and a furnace is not a good idea. Each fuel burning appliance requires a specific amount of diameter, slope, rise of the entire flue connected to it to ensure that the appliance operates safely and properly.

    Ask to see the venting table for the water heater that says that leaving it connected to the large chimney is recommended.
    Use the biggest hammer you like, pounding a square peg into a round hole does not equal a proper fit.

  6. #6
    Join Date
    Mar 2004
    Location
    Central NJ
    Posts
    25
    The second guy I had in for estimates said that the inspector usually lets it go on Bvents that travel up internal chases but fail it if it runs outside of an exterior wall. They have a preprinted line item on the extimate form for inserts but mine will be more work. It goes up a chase in my garage, turns nearly horizontal in the attic, then turns vertical again and exits the roof. I'm afraid I'm going to be forced to use a ventless.

    I appreciate the link to the NJ codes but I couldn't quite figure out what it was talking about (and I read standards documents for a living).

  7. #7
    Join Date
    Aug 2004
    Location
    S.E. Pa
    Posts
    6,180

    Thumbs down choices

    " I'm afraid I'm going to be forced to use a ventless."

    You mean Lung Vented...........

    The orphanned WH would need a liner or smaller B-vent.
    Hearthman

  8. #8
    Join Date
    Mar 2004
    Location
    Central NJ
    Posts
    25
    I don't know why I wrote ventless. I was thinking the alternative was a high efficiency power vented. My biggest problem with the liner is the convoluted way the existing b-vent is run. If it has to be taken apart to install the liner, wouldn't it be the same work to just fully change out the B-vent for the correct size? I went up on the roof and verified that it's a single wall, 9" diameter B-vent and the water heater output is 3". If I read the code correctly, the flue can't be more than 7x the cross sectional of the appliance feeding it. I'm screwed in that regard.

  9. #9
    Join Date
    Aug 2008
    Location
    Burlington , Mass
    Posts
    469
    Use a 95% condensing gas boiler for heat and domestic hot water using a superstor. You already have the new flue being installed on the boiler. It would save alot of time and aggrivation of installing flue system just for a water heater. The upfront cost will be a bit high but in the end you'll be safe of deadly flue gas, and you will very seldom run out of hot water. and you wont be doing the usual changing of gas water heater every 6 or 7 years, and you wont need any makeup air for the burner.
    I'll be there when I get there and not a minute later

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