Air Gap in boiler feed?

Dave in QCA

Hi all,  Strict back-flow regulations have arrived in Iowa!  Water service for commercial buildings including multifamily of 4 units or more, must now include back flow prevention.  If there are no "cross connections" a testable double check valve  at the service entrance is sufficient.  If there is a cross connection, such as to a boiler, then a reduced zone back flow prevention device is required.  This device reduces the pressure of the whole building (a very bad thing) and costs about twice as much as a testable double check valve, which does not reduce pressure.





If I can improve my boiler connection, I can use the double check at the service entrance.  There are 2 ways I can improve the boiler connection so as to remove the "cross connection".  One, I can install a reduced pressure zone back-flow prevention device.  Yes, the 1/2 size needed for the boiler cost much much less than the 1 1/4 size needed if I installed the same type of device at the entrance.  However, a reduced pressure device for the boiler would also have to be tested by a licensed tester each year along with the double check at the service entrance.  I proposed to the authority at the water company, that I could feed the boiler through an air gap device since my boiler runs at 8 oz of pressure or less.  She approved this approach.  It would have to be inspected by the water company to verify that there was an "air gap separation", but no ongoing annual testing would be required.





That finally brings me to the question at hand.  Has anyone else done this?  I am planning on running 1/2 copper pipe from the output of the fast fill valve and the MM 47-2 fill valve up to the ceiling level, where the fill pipe will pour into an "air gap" funnel device.  The outlet of the air-gap will be 1" pipe for 4', where it will reduce back to 1/2" and tie into the boiler piping at the same point that the present fill line connects.  My thought is that even if my vapor-stat failed and the pressure ran up to 1 psi, the setting on my pressuretrol, it would still not be enough to block flow of incoming water on a 48" tall open pipe.  I also would install a swing check below the water line, just for extra assurance.





The traditional Watts 9D Dual check is as good as nothing in the new plumbing code.  Incedentally, this is comming from the 2009 Uniform Plumbing code which Iowa recently passed as their current code.  Many states have not done so yet.  It is coming!





I may have not explained this very well, but I am wondering if anyone else has run into this problem, and if anyone has come up with the same idea to reduce the ongoing expense of testing and the one time outlay for expensive hardware.

Jamie Hall

Not exactly...

I've not run into exactly the same problem, Dave, but back in another life when I was one of the two building inspectors for the whole State of Vermont we did require backflow prevention on pretty much anything that wasn't drinking water.  We accepted both RPZ backflow prevention (and yes, they do drop the pressure in the building -- but only slightly) and air gaps -- and nothing else (except, oddly, vacuum breakers on urinals -- don't ask).  I never saw an air gap feed on a boiler, but I can't see any good reason why it wouldn't work just fine at the pressures we run these things at.  Just remember when you are piping the thing that one of the requirements for an air gap is that it be solidly mounted, and that the bottom of the opening of the feed pipe be at least two diameters above the highest point on the funnel or drain or whatever (funnel in this case) it is feeding into.