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Old 04-06-2013, 01:52 PM   #1
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Vacuum breaker with tankless water heater?

I'm getting ready to replace a leaking, power vented 40 gallon gas water heater with a tankless model. Plumbing code requires that a vacuum breaker be installed between the cold water shutoff valve and the cold water intake of the water heater.

The problem is placement of the vacuum breaker. Various places I've read indicate it must be 6" above the <fill in the blank>. Every tank type water heater I've looked at, as well as various online sources, shows the breaker 6" above the top of the heater. I suspect that's where it should be, relative to the tankless as well. Right?

But why it goes 6" above is puzzling. Since it's a bottom feed (and exit) tankless heater, perhaps it should be 6" above where the cold water goes into the heater? Note that both my cold and hot lines will be dropping down along the wall from the ceiling joist level in the basement. So, whether I place the tee off to the vacuum breaker 6" above the bottom, or 6" above the top, I don't know. And, do I/can I put in an elbow to raise it up higher, even if the tee is below the top of the heater?

One of my concerns is placement of the shutoff valves (not the cleanout/service valves, which attach directly to the bottom of the WH). I don't want to have them closer than 6" from the bottom of the joists, which then 'forces' the vacuum breaker down another 6", which then 'forces' the WH down yet another 6". Since I have 6-7" 'tall' service valves to attach, plus hot water pressure release valve, and drain valves for both hot and cold along the lowest points in each pipe, I'm getting terribly close to the floor for it all to 'fit'.

Lowering the top of the water heater more than about 12-13" from the joists also causes a condensate drain line problem as well. Lacking a floor drain in the house, I'm planning on running the condensate line to the top of the set tub in the basement, about 6 feet to the right of the heater. Any lower than currently planned, I'll either have to put a line directly into a copper and cast iron drain line from the set tub or get a condensate pump and deal with that, too. I'm familiar with the pump method as my high efficiency gas furnace uses one.

Any ideas or thoughts are most welcome.


Last edited by braman; 04-06-2013 at 01:55 PM.
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Old 04-06-2013, 03:12 PM   #2
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Why would you need a vacuum breaker on a tankless HWT.. Main word is tankless...


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Old 04-06-2013, 04:44 PM   #3
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Looked on line at the install directions for the heater?
I've never seen one on a tankless, there's no tank to sphion.
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Old 04-07-2013, 01:40 AM   #4
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As I have read in numerous places online, vacuum breakers, a form of backflow preventer, are required any time contaminated water (even that already in the pipes in my house) could be siphoned back into the water system. It would make more sense to me to simply put a backflow preventer directly after the meter, but that's more than I want to bite off.

From what I've read online, it's not a matter of tank or no tank. It's any water beyond that point as it could have lead from ancient solder, or whatever else in it. Even underground sprinkler systems require a vacuum breaker that's at least 12" above the ground level in some states.

And, for what it's worth, I've seen one tankless installation video on Youtube that included a backflow preventer connected right at the cold water inlet of the WH. THAT would make sense to me.
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