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Thread: Air Gap

  1. #1
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    Default Air Gap

    I saw this in my new construction inspection today. Never seen it before and it does not work.
    Comments are encouraged.

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  2. #2
    Joseph P. Hagarty's Avatar
    Joseph P. Hagarty Guest

    Default Re: Air Gap

    Never seen an install like that either.

    Hope that I never will....


  3. #3
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    Default Re: Air Gap

    I don't think that is a problem with it draining to the air gap, though not needed.
    I do see a problem with the discharge being that high off the floor.
    Also are those lines 3/4" CPVC?

    ' correct a wise man and you gain a friend... correct a fool and he'll bloody your nose'.

  4. #4
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    Default Re: Air Gap

    They are 3/4 cpvc.
    However when I lifted the the release for the drain line water went everywhere.
    The coupling acting as a funnel filled up almost instantaneously and the discharged water had no place to go.


    Captain


  5. #5
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    Default Re: Air Gap

    Absolutely wrong, presents a potential scalding hazard to occupants, get it done right.

    Jerry McCarthy
    Building Code/ Construction Consultant

  6. #6
    Richard Moore's Avatar
    Richard Moore Guest

    Default Re: Air Gap

    IRC(2006)
    P2803.6.1 Requirements for discharge pipe. The discharge piping serving a pressure-relief valve, temperature-relief valve or combination valve shall:
    1. Not be directly connected to the drainage system.
    2. Discharge through an air-gap located in the same room as the water heater.
    3. Not be smaller.....
    4. Serve a single relief device....
    5. Discharge to the floor, to an indirect waste receptor or to the outdoors. Where discharging to the outdoors in a area subject to freezing, discharge piping shall first be piped to an indirect waste receptor through an air gap located in a conditioned area.
    6. Discharge in a manner that does not cause personal injury or structural damage.
    7. Discharge to a termination point that is readily observable by the building occupants.
    8. Not be trapped.
    9. Be installed to flow by gravity.
    10: Not terminate more than 6" above the floor or waste receptor.
    11. Not have a threaded connection at the end of the piping.
    12. Not have valves or tee fittings.
    13. Be constructed of listed materials...

    Some of this is new for 2006. #2 and #5 seem to be a little repetitive.
    As for Mitchell's air-gap...it would meet the need for an air-gap, but then would appear to be in violation of #6. There is no way a full discharge is not going to splash back from that fitting. Hell, a full discharge would probably bend the CPVC(?) back enough so that nothing entered the receptor! It looks fine for catching and observing small leaks, but not much more.

    I have a feeling that the new air-gap requirements are more "subject to interpretation" than they should be. #13 states that the piping has to be "listed" materials but there doesn't seem to be anything about "listed" or "approved" air-gap designs.

    I suppose the re-write of that section was meant to clarify the requirements. I'm not sure they have done that.

    Last edited by Richard Moore; 10-18-2007 at 11:33 AM.

  7. #7
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    Default Re: Air Gap

    It does bend back the pvpvc when I released the valve. Of course I didn't release it all the way.
    It's just wrong but I have a feeling nothing will be done, I did my job and reported it and show how it didn't work to the super. And told my client to get in writing and signed if they don't fix it.

    Captain


  8. #8
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    Default Re: Air Gap

    They've got the right idea and are on the right track, but their execution was all wrong.

    Air gap too little (needs to be at least 1-1/2" for a 3/4" pipe).

    Receptor too small diameter (needs to be large enough to capture all the dispersing spray).

    T7P discharge line needs to be supported (to keep from kicking it up).

    Receptor too short (needs to be able to hold sufficient amount of water so that the water draining out can keep up with the water being discharged without overflowing the receptor).

    Jerry Peck, Construction / Litigation Consultant
    Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
    www.AskCodeMan.com

  9. #9
    Richard Moore's Avatar
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    Default Re: Air Gap

    Quote Originally Posted by Jerry Peck View Post
    Air gap too little (needs to be at least 1-1/2" for a 3/4" pipe).

    Receptor too small diameter (needs to be large enough to capture all the dispersing spray).

    .....

    Receptor too short (needs to be able to hold sufficient amount of water so that the water draining out can keep up with the water being discharged without overflowing the receptor).
    Jerry...in that first line, are you talking about the diameter of the receptor or the piping below?

    Not arguing here, actually anything but. But...even if the receptor was the size of a coffee can, and conical at the bottom to prevent splash back, I don't see how a continuation pipe below an air-gap, of the same size as the discharge pipe, could keep up with a full discharge. We all know that flow rate is dependant on pressure and "volume". With the continuation pipe effectively open to the atmosphere, the pressure in that pipe is going to be less than that coming out of the tank and the flow reduced. That might be somewhat mitigated, and back-up and overflow delayed, depending on the size and shape of the receptor, but I would still expect problems. It would seem to me that in order for a TPR discharge system with an air-gap to really function well, and not eventually flood the room during a discharge of any length, then the continuation piping below a well designed receptor would have to be increased in size. No?

    As the new code doesn't spell this out, I guess we can expect to see more "cobbled" systems that simply don't work and, probably, more water damage in the immediate area. I know that very few homeowners actually test their TPR valve yearly (as recommended by the mnfrs) but I would imagine even less doing so if it gets "messy" every time they do.


  10. #10
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    Default Re: Air Gap

    Quote Originally Posted by Richard Moore View Post
    Jerry...in that first line, are you talking about the diameter of the receptor or the piping below?
    The receptor.

    IF the receptor was large enough with a large enough drain, say maybe a 55 gallon drum with a 1" drain ... at some point ... the head pressure in the receptor would be sufficient to force enough water out the drain to keep up with the incoming water from the T&P discharge pipe.

    I guess I'm going to have to start doing to some testing ... cause I've been discussing this very same issue with a builder trying to figure out the best way to meet the requirements of the code.

    Jerry Peck, Construction / Litigation Consultant
    Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
    www.AskCodeMan.com

  11. #11
    Matthew Skowron's Avatar
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    Default Re: Air Gap

    If you read the stamping on CPVC it states that it is rated for 75-150 deg. a T&P discharges at 210 deg. 170 psi. I read some where that there should be no plastic pipe with in 18 inches of a water heater Ill look for that info and post it when i do.



    OH BY THE WAY CHECK THIS OUT
    Water Heater Blast!

    Last edited by Matthew Skowron; 10-19-2007 at 06:13 AM.

  12. #12
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    Default Re: Air Gap

    Quote Originally Posted by Matthew Skowron View Post
    If you read the stamping on CPVC it states that it is rated for 75-150 deg. a T&P discharges at 210 deg. 170 psi. I read some where that there should be no plastic pipe with in 18 inches of a water heater Ill look for that info and post it when i do.

    CPVC has been tested and listed for use as a discharge line from T&P relief valves.

    This is because, as the valve opens, the hot water which is discharging is being replaced with cold water from the inlet, which will drop the temperature of the water in the tank, which lowers the temperature of the water being discharged, which is replaced by cold water from the inlet, which lowers the temperature of the water in the tank, which lowers the temperature of the water being discharged ...

    ... to a point, and fast enough, that the CPVC is not compromised.

    Jerry Peck, Construction / Litigation Consultant
    Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
    www.AskCodeMan.com

  13. #13
    Brandon Chew's Avatar
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    Default Re: Air Gap

    The flow rate coming out of the water heater TPR line is going to have a minimum of the house supply pressure and a max of about 150-170 pushing it out. Once it hits the air gap that pressure is now reduced to atmospheric. If the inside pipe diameter after the air gap is the same size as the inside pipe diameter before it, the only way the drain will be able to keep up with the flow coming into the receptor is if you find some way to put at least the same amount of pressure back on the water.

    The practical implications of what I just wrote are:

    If you use the same size pipe after the air gap as the line feeding it, you are going to have to blow it into a sump and then pump it out (in order to get the pressure back on the line).

    If you want it to drain away by gravity, then you will need to increase the size of the line after the air gap. For it to work properly, this line needs to be sized like a DWV line serving a fixture with a flow that is equivalent to that coming out of 3/4" pipe flowing full at house supply pressure (like a wide-open hose bib or laundry sink faucet), because that's the kind of continuous flow you will have if the TPR valve blows and sticks in the open position. Use DWV sizing because the flow regime after the air gap is a pipe that is not flowing full and is at atmospheric pressure.

    Theoretically there are more options than the above that would make the same size pipe before and after the air gap work, but I don't think they are practical (e.g., develop a water column high enough to create 170 psi at the bottom...have a large volume receptor that will act as a flow equalization tank, but this would still need an emergency overflow that would drain by gravity to a safe location in order to protect against water damage -- if the discharge from the TPR continues long enough, the tank WILL overflow.)


  14. #14
    Richard Stanley's Avatar
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    Default Re: Air Gap

    This was also in the 2003 IRC, but, applicable only to freeze areas. Anybody up north got a pic of how they do this?? Still trying to figure out why it's needed. Over kill. Would some type of an AAV work?


  15. #15
    Peter Drougas's Avatar
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    Default Re: Air Gap

    In New Hampshire water heaters are typically in basements and the line (when installed correctly) simply discharges about 6" off the floor. In Mobil homes it just drops straight through the floor. The only questionable installation I have seen up here (besides the usual mistakes) is in apartment condo's where the tank is in a closet and the discharge line goes straight across into a wall, never to be seen again!


  16. #16
    Richard Stanley's Avatar
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    Default Re: Air Gap

    Time to get serious.
    The air gap is the space between termination and the floor / ground / waste receptor. Max 6" interior, 6 - 24" exterior.
    The big box is giving away a free case of TP air gaps with every purchase - so I heard.


  17. #17
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    Default Re: Air Gap

    Quote Originally Posted by Richard Stanley View Post
    Max 6" interior, 6 - 24" exterior.
    Huh?

    Where did you get those dimensions from?

    The minimum air gap is 1" or 2 times the diameter of the pipe discharging the waste - meaning a 3/4" pipe requires a minimum 1-1/2" air gap.

    Jerry Peck, Construction / Litigation Consultant
    Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
    www.AskCodeMan.com

  18. #18
    Richard Stanley's Avatar
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    Default Re: Air Gap

    I don't know where the minimums are stated - so if the termination was min. 1 1/2" (for 3/4" pipe) above the surface and within the maximums, it should be good, eh?


  19. #19
    Jim Entwisle's Avatar
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    Default Re: Air Gap

    I was near one when it released and it was not nice.... it started with a loud bang then steam .... the steam came out horizontally and 360 degrees around the opening of the discharge pipe.... it did not discharge vertically.... the one in the picture would certainly spray scalding steam into the face of anyone standing nearby because it is as high as the top of the water heater and not within six inches of the floor.... the purpose of it being six inches above the floor is to prevent scald injury and to notify the owner that something is wrong with the water heater and it needs professional servicing (because he sees water on the floor).... when the discharge is out of sight then the owner has no knowledge that something is wrong with his water heater and it could lead to an explosion .... I always refer the buyer (owner) to the water heater manufacturer's installation instructions when I question the installation....


  20. #20
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    Default Re: Air Gap

    Quote Originally Posted by Jim Entwisle View Post
    the purpose of it being ... and to notify the owner that something is wrong with the water heater and it needs professional servicing (because he sees water on the floor)....
    when the discharge is out of sight then the owner has no knowledge that something is wrong with his water heater and it could lead to an explosion ....
    Okay, so ...

    If the purpose is to let the owner/occupant know, why are water heaters allowed to be installed in ...
    - attic
    - storage closets
    - out of the way places where the discharge has no hope of being seen until great amounts of water damage due to flooding has been done?



    I've talked to many Chief Plumbing Officials about this and they all agree on one thing, that they would prefer that the water be installed in ...

    ... the middle of the living room - so this will be readily observable by the occupants!

    Of course, they also acknowledge that installing the water heater in the middle of the living room is not really a good idea, and no one would go for it even if it was a good idea, so, I asked 'Why let them install the water heater in the attic or in a storage closet where it will never be seen?', 'Because we cannot tell them where they can and cannot install the water heater.' is their reply. I asked 'Then seeing the discharge is not really that big of an issue, is it?', 'Yes, it is, but we cannot control it.' I said 'You could if you wanted to and really thought it was that big of an issue, simply by making those requirements in the code.', 'We can't do that, no one would do that anyway.' I said 'Let me get this straight, then, you want it there so it can be seen, but you are not going to enforce it to be seen?', 'Right.' they said.

    Anyone else but me see the conflict in what they are saying there?

    In my opinion (which means little there) is that *IF* the intent is "to be able to see the water", then that means that *water is running*, right?

    And, if water is running, *AT THAT POINT*, (that bears repeating, *AT THAT POINT* - *with the water running*) the safety explosion issue has passed - it passed *as soon as* the T&P relieved itself.

    If *THAT* (the explosion issue) is the issue (and it is), then what is wrong with the T&P discharge draining to the outside like it used to?

    None.

    With the T&P discharge draining to the outside, the water heater will no longer make hot water, probably make it barely warm ... THAT (no hot water) will get the occupants to check it out or call a plumber!

    The end result is now the same as flooding the inside of the house.

    Jerry Peck, Construction / Litigation Consultant
    Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
    www.AskCodeMan.com

  21. #21
    Richard Stanley's Avatar
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    Default Re: Air Gap

    FWIW, you are correct. How about an alarm? Bells and whistles! The cool water is a silent alarm. Probably not that silent - step into cold water in the tub / shower.


  22. #22
    Matthew Skowron's Avatar
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    Default Re: Air Gap

    Of course, they also acknowledge that installing the water heater in the middle of the living room is not really a good idea, and no one would go for it even if it was a good idea, so, I asked 'Why let them install the water heater in the attic or in a storage closet where it will never be seen?', 'Because we cannot tell them where they can and cannot install the water heater.' is their reply. I asked 'Then seeing the discharge is not really that big of an issue, is it?', 'Yes, it is, but we cannot control it.' I said 'You could if you wanted to and really thought it was that big of an issue, simply by making those requirements in the code.', 'We can't do that, no one would do that anyway.' I said 'Let me get this straight, then, you want it there so it can be seen, but you are not going to enforce it to be seen?', 'Right.' they said.
    Looks like a case we all deal with "He who has the money makes the rules"
    none of us like it but if you think about it its the way our buisness works.

    We inforce rules no one wants us to inforce, we fight to save people that dont want to be saved. ( IMO: If we do our jobs FireFighters dont have to do there's)

    I went to Arlington BPI confrance and heard that the NFPA was going to fight to get Waterheaters out of attic's due to killing fire fighters. When they go in to debree the scene and pull the 40 gal heater down on them selves and never knew it was there it isnt good ( not to mention the 3-4 replacements left up there). from what i have been told Dallas TX has out- lawed heaters in attic's (someone conferm or debunk).


    Matt

    Definition- IMO= In my Opinion


  23. #23
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    Default Re: Air Gap

    And apparently all of you find it appropriate to actually tamper with the relief valve. Not me. You just hope it re-seats itself I guess. Because if it doesn't, you go some 'splaining to do.
    JLMathis


  24. #24
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    Default Re: Air Gap

    Jeff,

    You might want to check out the current thread.


    Leaking TPR Valve.

    It Might have Choked Artie But it ain't gone'a choke Stymie! Our Gang " The Pooch " (1932)
    Billy J. Stephens HI Service Memphis TN.

  25. #25
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    Default Re: Air Gap

    Quote Originally Posted by Jeffrey L. Mathis View Post
    And apparently all of you find it appropriate to actually tamper with the relief valve.
    "tamper with"

    Raising the *TEST* lever is not "tampering with", it is considered a REQUIRED TEST.

    If you don't think so READ A TAG ON ONE SOME DAY.

    Jerry Peck, Construction / Litigation Consultant
    Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
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