Drain options for landlocked water heater

Old 02-24-17, 06:36 PM
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Drain options for landlocked water heater

Hi All,

I am considering replacing our existing tank-type water heater with a tankless. The heater is in a hall utility closet and the building is on a slab foundation. There is no floor drain installed in the closet and there is no good route for a PRV drain line out to the outside of the building. However, there is a lavatory sink on the other side of the wall that I could potentially tie an indirect waste pipe to. My governing code is the California Plumbing Code 2016, no local amendments.

Section 608.5 requires that the discharge from a pressure relief valve be directed to the drainage system via an air gap (i.e. indirect waste pipe) or discharged outside. This section also prohibits the discharge pipe from being trapped.

Section 812.1 says that clear water wastes from appliances, drip pans, etc, should be discharged to the drain system via an indirect waste pipe.

Section 804.1 says that no indirect waste receptor can be installed in a closet, cupboard, or other part of the house not in routine usage by the occupants.

So the code seems to be telling me to install an indirect waste receptor but it's also telling me I can't install such a receptor in the utility closet where the water heater resides.

Has anyone run into this issue before? Can you install an indirect waste receptor serving the water heater PRV adjacent to a water heater in a utility closet and then pipe that waste to a lavatory tailpiece?

Any thoughts would be welcome.
Old 02-24-17, 06:49 PM
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I am not the pro here but my thoughts are you wouldn't want a pressure relief line discharging into a sink drain line as it could cause heat/steam injury to someone standing at the sink if it discharged.
Old 02-24-17, 07:32 PM
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That's a good point and I recall reading some IPC code sections that basically said that you couldn't discharge into a lav. But that doesn't seem to be in the CPC. And the presence of the air gap means that the water going into the waste pipe is only under the pressure of gravity, which reduces the chance of a big geyser of water in the sink basin. Still, it's worth consideration.

Unfortunately, if I have to drain the PRV to the outside, it means opening up an entire bathroom wall since I can't run it uphill to the attic first.

If I stick with a tank-type water heater, I can go with a Watts 210 valve and a PRV at a more convenient location, but I'm still stuck with running an indirect drain for the drip pan. That said, the drip pan isn't going to ever create enough flow to blow water up into the sink.
Old 02-24-17, 08:15 PM
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A permit is required to install a water heater. The local inspector should work with you and explain the PRV drain requirements.

Here's a good guide, courtesy of the city of Concord:

Here's one quote:
When approved by the Chief Building Official, such drain may terminate at other
locations (i.e. laundry tub, floor sink, or floor drain). No part of such drain shall be trapped and the terminal end of the drain shall not be threaded.

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