# On demand gas water heater in a crawlspace



## retire09 (Dec 19, 2013)

I have a house with a gas, on demand water heater mounted to the foundation wall in a crawlspace.

The location is in Alaska with -30 temperatures outside.

The crawlspace is heated and has a vapor retarder covering the ground.

Where do you terminate the T&P drain line from the heater?


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## Gregg Harris (Dec 19, 2013)

retire09 said:
			
		

> I have a house with a gas, on demand water heater mounted to the foundation wall in a crawlspace.The location is in Alaska with -30 temperatures outside.
> 
> The crawlspace is heated and has a vapor retarder covering the ground.
> 
> Where do you terminate the T&P drain line from the heater?


504.6 Requirements for discharge piping. The discharge piping serving a pressure relief valve, temperature relief valve or combination thereof 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 than the diameter of the outlet of the valve served and shall discharge full size to the air gap.

    4. Serve a single relief device and shall not connect to piping serving any other relief device or equipment.

    5. Discharge to the floor, to the pan serving the water heater or storage tank, to a waste receptor or to the outdoors.

    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 so as to flow by gravity.

    10. Not terminate more than 6 inches (152 mm) above the floor or waste receptor.

    11. Not have a threaded connection at the end of such piping.

    12. Not have valves or tee fittings.

    13. Be constructed of those materials listed in Section 605.4 or materials tested, rated and approved for such use in accordance with ASME A112.4.1

#7 would be hard to accomplish, but it could discharge into a pan with an alarm to notify the occupants.


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## mtlogcabin (Dec 19, 2013)

If I am not mistaken Alaska is under the 2009 UPC.

The UPC does not permit the T&P to discharge into the crawlspace. You can only run a T&P discharge pipe horizontal or vertically downward.

Therefore the state of Montana has issued an interpretation a water heater can not be located in a crawlspace

With that said can you mount the unit high enough to horizontally discharge the piping to the garage through the rim? It will be visible to the occupants if it leaks and it will not freeze as easily in the garage on the house side. The garage floor will need to be below the house floor joist.


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## retire09 (Dec 19, 2013)

That would be a great idea, but we can't  get enough height.

I have thought about allowing it to go through the vapor retarder and into an open pit that would soak into the ground below. Like a 5 gal bucket with no bottom. The ground here is all sand and gravel that will soak this up easily.

I know it's not code compliant but is there a better way?

I don't see this as a life safety concern and would rather not disallow the use of the crawlspace.

Any other ideas?


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## Gregg Harris (Dec 19, 2013)

retire09 said:
			
		

> That would be a great idea, but we can't  get enough height.I have thought about allowing it to go through the vapor retarder and into an open pit that would soak into the ground below. Like a 5 gal bucket with no bottom. The ground here is all sand and gravel that will soak this up easily.
> 
> I know it's not code compliant but is there a better way?
> 
> ...


The only issue with it terminating into a french drain is that it would go unnoticed. I would have it discharge into a pan first with a water sensing device that has an audible alarm to the occupied space, and then into the french drain.


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## markw (Dec 23, 2013)

Put a condensate pump on it. Prob got 120v there anyway for the WH. Pumps have float with a overflow switch that can be wired up for shutdown.Your welcome.


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## ICE (Dec 24, 2013)

markw said:
			
		

> Put a condensate pump on it. Prob got 120v there anyway for the WH. Pumps have float with a overflow switch that can be wired up for shutdown.Your welcome.


I haven't seen a condensate pump that could handle the flow.


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## Sifu (Dec 24, 2013)

IN one previous jurisdiction we terminated them into a gub which gave us the air gap and termination in the same room.  Then the hub ran outside to a conspicuous location.  Here we allow a sump to get it out since we are deeper in the ground and can't get gravity to work in our favor.  Not sure either works to effectively alert the occupant of a weeping T&P.


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## Francis Vineyard (Dec 24, 2013)

Do not know what the UPC requirements are but the code, standard and manufacturers do not require a temperature relief valve for tankless appliances.   The pressure relief valve can be installed in either the cold or hot water line as long as a valve is not between it and the heater.   The discharge could then be inside where not subject to freezing.


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## mark handler (Dec 24, 2013)

Most tankless heater units I have seen require a pressure only relief valve on the hot water output. Pressure only valves such as Cash Acme FWL-2, Zurn P3000BR, or Watts 174A would be required. Temperature sensing is done internally via an integral hi-limit switch.

Refer to the manufactures installation instructions

As to the discharge, you could allow the discharge into a sewer pipe with a "sensor" alarm alerting the owner


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