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  1. #1
    Join Date
    Feb 2010
    Location
    Manassas, VA
    Posts
    15

    Orphaned water heater venting question

    We are in the process of getting a new split-system and during the visit by one of the possible contractors he mentioned that the we might not be able to install a high efficiency furnace, since that would orphan the existing 40k BTUH water heater. The obvious question is - is the current vent (6" OD Type B) too big? The run from the water heater to the vertical vent is about 5 feet and is 4" single walled pipe. The vent itself is is about 35'-40' long (furnace is in basement of a two story house). Looking at this: http://www.hartandcooley.com/Librari...?download=true (Page 9, bottom right), it would seem that the current vent is not too big (10 inches being the max). Having done a search on this site, I see that others have had to have a smaller pipe liner installed, which I really don't want to do if I don't have to beaciuse of the added cost. My first inclination is to trust the contrator's word, but I don't want to limit myself to another 80% furnace if I don't have to.

    The other contractor that has visited mentioned nothing about the venting system.

    On another note - As a new member, thanks to you all for contributing on this site and answering the questions of us homeowners. I have been lurking here for the past few weeks and it has been eye-opening to learn all the in's and out's of the process needed to replace our current system. Seems trying to get a contractor to do a Manual J calulation is like pulling teeth. I have done my own using HVAC Calc, but so far neither contractor that have visited have offered to do one. In fact the second asked why I wanted one done (but that's another story yet to be completed...).

  2. #2
    Join Date
    Jul 2009
    Location
    Ontario, Canada
    Posts
    913
    Have the contractor check with local codes. Im sure a liner down the flue should do the trick. The size of liner also depends on btus of current water heater, as well as chimney height that you mentioned. Have him check the code book for proper verification.

  3. #3
    Join Date
    Jun 2006
    Location
    Richmond, VA
    Posts
    2,827
    Trust the contractor that knows to do it right. Orphaning water heaters is a huge problem when converting to a 90 plus. I do manual J's on every job and its great that someone has done the research to understand the importance of doing a job right
    Give a man a fish, he will eat for a day. Teach a man to fish, he will eat for a lifetime.

    Give a man a capacitor, doesn't know what to do. Teach a man to install it, now he knows everything.

  4. #4
    Join Date
    Jun 2003
    Location
    West of Ottawa Ontario
    Posts
    310
    Just drop a proper liner and be done with it. In Canada, Ontario in particular, outdoor b vent is causing issues. Issues in the sense that tightening regulations want us to use liners, power vent, or direct vents. Outdoor bvent will be the way of the do-do soon. Orphaned water heaters need to have the proper size vent to ensure no condensing in the chimney of flue products. Where I live, an orphaned Hwt can go up a 6'' liner or b-vent provided the bvent is in an interior space( chase in interior wall or engineered and built with the house on the outside wall), or in an existing brick chimney lined with bvent or a liner. The waterheater input has to be larger than 30000 btu, and the combustion air is also a consideration. I personally would drop a liner, use bvent on the inside portion to keep up exhaust temp. Just make sure your local contractor follows the "regs". I like natural draft tanks, they are quiet,dependable, use no electricity.
    Last edited by polar ice; 02-21-2010 at 07:13 PM. Reason: I was stupid....had to edit myself
    Save me Jebus

  5. #5
    Join Date
    Jul 2008
    Location
    Rochester NY
    Posts
    4,696
    Eventually natural draft appliances will be gone. Get the 95, they are so nice and the incentives are too good to be true.

    Assuming there is no liner, How old is water heater?
    Which makes more sense to you?
    CONSERVATION - turning your thermostat back and being uncomfortable. Maybe saving 5-10%
    ENERGY EFFICIENCY - leaving your thermostat where everyone is comfortable. Saving 30-70%

    DO THE NUMBERS! Step on a HOMESCALE.
    What is comfort? Well, it AIN'T just TEMPERATURE!

    Energy Obese? An audit is the next step - go to BPI.org, or RESNET, and find an auditor near you.

  6. #6
    Join Date
    Feb 2010
    Location
    Cal
    Posts
    1,596
    Ask your contractor to explain page 17/bottom of the referenced guide. The warm/buoyant flue gas needs to be creating a draft. A properly sized flue will but not one drastically super sized. The building inspector will have the final opinion on what will be allowed so why not ask now. Submit a detailed drawing with what you propose/have, then have your contractors bid on what CODE ALLOWS.

    PS- The flue is the same size year round, how many appliances are using the flue/chimney during the summer months and what has been the outcome ?

  7. #7
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,704
    Is this a B vent chimney inside the house?
    Contractor locator map

    How-to-apply-for-Professional

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

  8. #8
    Join Date
    Aug 2002
    Location
    Southold.calm
    Posts
    5,414
    Quote Originally Posted by btuhack View Post

    PS- The flue is the same size year round, how many appliances are using the flue/chimney during the summer months and what has been the outcome ?
    In the summer months the flue is 50 to 60* warmer.

  9. #9
    Join Date
    Feb 2010
    Location
    Cal
    Posts
    1,596
    Quote Originally Posted by pecmsg View Post
    In the summer months the flue is 50 to 60* warmer.
    Your point is well taken and the thought was considered prior to "submit" The furnace is off at 70 osa, agreed? So what is the ambient at the bvent-(see beenthere) now? 10?
    Also, b-vent liner is designed to warm quickly to minimize troubles relating to your concerns.

    A lined/sized flue is ideal for sure, but if code allows the existing and the mfg supports the concept, my earlier posting has merit.

  10. #10
    Join Date
    Aug 2003
    Location
    Central Kentucky
    Posts
    6,247
    Gotta agree with tedkidd, natural draft appliances should be gone.
    The draft hood should have been deep sixed years ago.

    A flue liner won't magically make a natural draft water heater installation safe, it might even cause the reverse to occur
    Have you set up a Google alert for Carbon Monoxide yet?
    Click here to find out how.

  11. #11
    hearthman's Avatar
    hearthman is online now AOP Committee/Professional Member*
    Join Date
    Aug 2004
    Location
    S.E. Pa
    Posts
    6,136

    Cool

    If the B-vent is routed through the interior of the home, then at 6" it is probably acceptable. Obviously, a properly sized liner is ideal but.......

    No liners are listed for use inside B-vent. Functionally, it shouldn't be a problem but a sharp AHJ could flag it. You can vent a 40K WH into up to a 7" round so it is 'legal' but that doesn't necessarily make it a good idea. The standing pilot will help a little but not much. There is no post-purge of a WH so summertime condensation can be a real problem not to mention there is almost no natural draft in summer.

    For the cost of a liner, you have to consider switching to a power vented model instead. If not and you do reline, use a 315Ti stainless steel that carries a transferrable lifetime warranty and use B-vent for the connector.

    HTH,
    Hearthman

  12. #12
    Join Date
    Jul 2004
    Location
    Massachusetts
    Posts
    6,829
    Obviously I can't speak for other jurisdictions but in ours, it's a simple math question for b-vent. If the chimney for the appliance (any appliance, not just water heaters) is more than 7X the area of the appliance vent connector pipe then a new chimney or chimney liner must be used or buy a new appliance that sidewall vents. In the case of a 40,000 Btu unit, that should have a 4-inch vent connector which is 12.56 sq. in. X 7 = 87.92 sq. in. So any vent of at least 12.56 sq. in. area and not more than 87.92 sq. in. area will work nicely. A 6-inch B-vent has an area of 28.26 sq. in. and so will work with no problem, at least in our jurisdiction, which I believe is fashioned quite closely to the National Gas Code. But my code book is in the truck, which is outdoors where it's cold so no, I'm not going there to find chapter and verse on this. Suffice it to say I just finished my annual continuing ed class last week and that was a topic of discussion.
    If YOU want change, YOU have to first change.

    If you are waiting for the 'other guy' to change first, just remember, you're the 'other guy's' other guy. To continue to expect real change when you keep acting the same way as always, is folly. Won't happen. Real change will only happen when a majority of the people change the way they vote!

  13. #13
    Join Date
    Feb 2010
    Location
    Manassas, VA
    Posts
    15
    Thanks to all for your replies! I obviously will go with what the chosen contractor recommends and now also know to ask the other contractors about it. As you all have said - local code and the inspector will have the final say. Unfortunately, the vent takes a couple of 45* bends in the attic before exiting through the roof, so it wll be more than a simple liner install up a straight pipe. I had hoped to avoid that due to cost.

    This contractor was also concerned at the length needed for the new PVC intake/exhaust pipes for a high efficiency furnace. The current unit sitts in the front middle of the basement with all the nearest walls not suitable for the exhaust (Garage, windows or gas meter there). The only suitable exit point is about 35' away (with a few right angle turns needed to get there) and the contractor was also worried about that. A high efficiency may not be in the cards for us...

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