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Thread: Tie sink vent & boiler vent together?

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    DIY Junior Member zaothusia's Avatar
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    Exclamation Tie sink vent & boiler vent together?

    I have a wall mounted high efficiency boiler. It is direct vented with 3 inch PVC outside the house. I am going to be adding a sink and need to vent it quickly, can I tie into this, or will it cause my boiler to run less efficient?

    If I cannot tie into this I am wonder if anyone knows if an AAV is legal in Minneapolis, Minnesota? I would prefer to not have to redo this in the future

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    Plumber krow's Avatar
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    Quote Originally Posted by zaothusia View Post
    I have a wall mounted high efficiency boiler. It is direct vented with 3 inch PVC outside the house. I am going to be adding a sink and need to vent it quickly, can I tie into this, or will it cause my boiler to run less efficient?
    Don't you dare try that. You could end up killing yourself if any methane gas gets in the boiler while its firing, if you don't blow up the neighbourhood first

    I'm not sure if AVV's are legal in Minneapolis, but it would be better than the original idea.

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    Journeyman & Gas Fitter Doherty Plumbing's Avatar
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    Quote Originally Posted by zaothusia View Post
    i have a wall mounted high efficiency boiler. It is direct vented with 3 inch pvc outside the house. I am going to be adding a sink and need to vent it quickly, can i tie into this, or will it cause my boiler to run less efficient?
    no..................

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    Got to be the best post of the year

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    Moderator & Master Plumber hj's Avatar
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    Default vents

    That would not be the best idea you have had this year, nor the smartest one. I can just imagine someone doing that, and then using AAV's on all the other drains and wondering why NOTHING drains properly while the boiler is operating.

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    DIY Junior Member Daltex's Avatar
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    I know you wouldn't have posted this if you understood the implications of doing it. Quick answer is for a quick vent use an AAV if only for the one sink. May not be code so you might want to check it out with the city first. They are not quiet btw.

    Problems with connecting the vent to the boiler vent=

    When the boiler fires, it will have positive pressure running in the vent. This could/would cause the exhaust along with the CO and combustion by products to push its way through the sink's p-trap and cause deadly gas to be released inside your home.

    The vent from the sink will be connected to the main sewer line which has methane gas and odors. When the blower is in between cycles, the methane could be vented back inside your boiler. When ignition occurs- bang! There is no p-trap on the exhaust vent so it could also fill the room with methane along with the sewer odor.
    Last edited by Daltex; 01-05-2010 at 02:04 PM.

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    Journeyman & Gas Fitter Doherty Plumbing's Avatar
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    Quote Originally Posted by Daltex View Post
    When the boiler fires, it will have positive pressure running in the vent. This could/would cause the exhaust along with the CO and combustion by products to push its way through the sink's p-trap and cause deadly gas to be released inside your home.
    What deadly gases? A properly burning gas appliance doesn't produce any deadly gases. You could obviously produce carbon monoxide but it's not a regular byproduct of combustion in anything close to deadly amounts. But don't get me wrong I'm certainly not trying to say this guy should hook up his plumbing vent to his gas vent.


    Quote Originally Posted by Daltex View Post
    The vent from the sink will be connected to the main sewer line which has methane gas and odors. When the blower is in between cycles, the methane could be vented back inside your boiler. When ignition occurs- bang! There is no p-trap on the exhaust vent so it could also fill the room with methane along with the sewer odor.
    You know that natural gas and propane (the stuff being burned in the boilers) are just forms of hydrocarbons so is methane (in fact NG is basically methane).

    Not only that all boilers that are electronically ignited have a prepurge time of the fan to clear the combustion chamber of any gases.

    And on top of that you need the proper mixture of air to methane to combust it. So is it possible that you could ignite methane from the sewer inside the combustion chamber and have it explode all the way back into the city sewer..... absolutely not.

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    Jack of all trades frenchie's Avatar
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    Quote Originally Posted by Doherty Plumbing View Post
    What deadly gases? A properly burning gas appliance doesn't produce any deadly gases. You could obviously produce carbon monoxide but it's not a regular byproduct of combustion in anything close to deadly amounts. But don't get me wrong I'm certainly not trying to say this guy should hook up his plumbing vent to his gas vent.




    You know that natural gas and propane (the stuff being burned in the boilers) are just forms of hydrocarbons so is methane (in fact NG is basically methane).

    Not only that all boilers that are electronically ignited have a prepurge time of the fan to clear the combustion chamber of any gases.

    And on top of that you need the proper mixture of air to methane to combust it. So is it possible that you could ignite methane from the sewer inside the combustion chamber and have it explode all the way back into the city sewer..... absolutely not.

    http://www3.gendisasters.com/idaho/1...osion-may-1916

    http://query.nytimes.com/gst/abstrac...649D94659ED7CF

    http://query.nytimes.com/gst/abstrac...6E9C94649ED7CF

    http://news.google.com/newspapers?ni...g=3887,1484502

    http://news.google.com/newspapers?ni...g=5847,1487983

    http://www.wreg.com/news/archive/hol...,4337430.story
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    Journeyman & Gas Fitter Doherty Plumbing's Avatar
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    Only the last article is from post 1930 and it doesn't even say conclusively that it was sewer gas that caused the explosion in the house. They just had no other explanation so they picked sewer gas as the culprit. Certainly not rock hard evidence.

    All the other articles (glanced over them quickly) were caused from someone actually down inside the main sewer with an open flame or another source of ignition like a short in some underground wiring. Again they were all basically from 80+ years ago too.

    So I don't think any of those articles prove what I said is wrong. I'm not saying sewer gas can't be explosive but the chances of a HE boiler with a positive vent pressure lighting up your neighbourhood's sewer is 0%.

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