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  1. #1
    Join Date
    Jan 2008
    Posts
    7

    powervent water heater

    2-3 weeks ago I had installed a 75 gallon A.O. SMITH powervent water heater. The question is --- isn’t there supposed to be a post purge on the tank after it shuts off. It has a pre purge of 30 seconds before the tank goes on. But after the tank shuts off , the powervent only runs for 3-4 seconds. Then I get a constant back draft and all the fumes end up dumping back into the house. Currently I operate the tank manually, then go out and tape a bag around the vent cap. Otherwise everyone in the house including the animals have health problems.
    The house doesn’t have a chimney or smokestack effect – but it does end up having negative pressure due to stove fan, bath fans, dryer, and especially the powervent. I’ve contacted A.O. SMITH, and after almost 3 weeks of emails to them – they cant tell me a thing. They don’t know how long it is supposed to run for or even if it is even supposed to have a post purge. It’s like asking a politician a question – you get all sorts of answers, but not the answer to the question. I looked at other companies, such as Bradford White. They have a 15 second pre-purge, and a 15 second post purge. The contractor who did an excellent job installing a new furnace, is clueless about the water tank, that it is even supposed to have a purge system. The house was checked for CO, but none was found anywhere in the house. Which leads me to my final question – if CO doesn’t come out of the tank then what gases do. I have talked to at least 5 different contactors in the past 6 months and not one can tell me what gases come out of the tank or a furnace for that matter. The mind set seems to be that if there isn’t any CO , then you don’t have a thing to worry about. So is the tank defective? And what in fact does come out of the tank other than CO? thanks.

  2. #2
    Join Date
    Dec 2002
    Location
    Toledo, Ohio, United States
    Posts
    12,921
    Twilli says call the guy that installed it and have him fix the problem.
    No Heat No Cool You need Action Fast

  3. #3
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,611
    I find it hard to believe that what little flue gases come out after the burn cycle are really affecting anything/anybody. If all is burning right, CO is a tiny part of the combustion products. Most are Co2 and water vapor. I've put a meter on many water heaters, usually get around 11-12 ppm. A smoker's breath can read 10 times that.

    We had a house that the furnace has been venting into the basement due to a plugged flue all winter. They had no symptoms other than condensation in the plugged flue which is why they called. This is probably hundreds of times the amount you get from your water heater.

    Probably a way to rig up a post purge put seems to me if the mfr. thought it necessary, they would have done it.

  4. #4
    Join Date
    Mar 2005
    Location
    Suppy NC
    Posts
    4,517
    installed a lot of ao smith dirrect vent and there is no post purge
    once the gas shuts down there are no biproducts being made.

    If your house is in that much of a negative pressure then you need to look into resolving it rather then redesigning all of your appliances

  5. #5
    Join Date
    Jul 2004
    Location
    Massachusetts
    Posts
    6,841
    Quote Originally Posted by tinknocker service tech View Post
    installed a lot of ao smith dirrect vent and there is no post purge
    once the gas shuts down there are no biproducts being made.

    If your house is in that much of a negative pressure then you need to look into resolving it rather then redesigning all of your appliances
    I agree. If all your vented appliances leak back into the home, why focus on the water heater? You need to pressurize the home as now it is under a negative pressure for whatever reason. You say the house doesn't have a chimney effect? How do you know? Did you have a blower door test done? If you already know the house is under negative pressure, why not cure that problem? Other than a few oil boilers, I've yet to find any other piece of residential combustion equipment that's designed to run when the room is under a negative pressure. A simple solution, rather than covering the exhaust after ever water heating cycle, is to open a window. If that doesn't do the trick, open two. That'll get rid of the negative pressure for sure. And it'll be a lot less work and a lot safer than putting a plastic bag over the exhaust.
    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!

  6. #6
    Join Date
    Mar 2001
    Posts
    1,213
    The contractor that did the 'excellent' job of installing your furnace should have dealt with the negative pressure issue. Probably all you need is passive make-up air, & some mechanical make-up air to set it right. This should be covered in your building code & fuel gas code.

  7. #7
    Join Date
    Feb 2004
    Posts
    2,597
    3 letters

    ERV (or 2)

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