From my google searching, I understand this is a very common forum thread.

Background:
House is 2 years old, located in NC
3 stories, with crawlspace, crawlspace tall enough to walk around in
Existing piping is all PVC / PEX
Community well (run by a private company)
Septic in back-yard, gravity fed from house, no pump

The logical place to install the water softener is in the crawl space next to the door, which is also where the well water enters the house. It's all 1" PEX inside the crawl space. There is an existing cartridge particulate filter at that location.

I'm not concerned with the supply side, that's very straight forward, with the typical 2 ea. 1" FNPT fittings. I'll tie-in to the existing PEX piping just downstream of the filter. The backwash drain is the typical 1/2" poly tubing.

Because there isn't a floor drain / washing machine (located up on the second floor), there isn't a great place for the drain to connect into. The nearest drain piping is directly below a half bath on the first floor. There is a 2" from the sink, and a 3" from the toilet. I suspect this same 3" drain also serves a bath, and laundry room on the second floor.

AS you can see from the photos, there is not a lot of space above the 2" line. I would need to tuck the trap, and the vertical section up in the joist cavity. There is about 18" from top of pipe to bottom of floor decking.

There is more vertical space above the 3" as you can see.

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I envision need a Y to a P-trap to a vertical section to an air gap fitting. Like this (stolen from internet):

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Any thoughts on whether I should tap into the 2" line or the 3" line. Am I missing anything else?

Thanks!

Glenn

I would tap the 3" line as that gives you more vertical space for the standpipe.

I would not have an open drain in the crawl space. If you have a stoppage down the line water would back up out of the drain and you wouldn't notice since it's under the house. I'd install a hi flow dual inlet air gap at the kitchen sink and pipe the discharge to it.

Thanks for the responses so far. The open drain does make me a bit nervous, as you are correct, we only visit the crawl space every couple of months to change the cartridge filter currently.

The first floor kitchen sink is not a large vertical run, and is probably a 15' horizontal run, so head pressure wouldn't be an issue I don't think. The sink doesn't have a disposal, but the dishwasher is plumbed into one of the bowl drains above the p-trap. There is no air gap currently installed, presumably the builder used a high loop.

It's on an interior wall, with a large window over the sink. It has a Studor RediVent AAV where the drain goes into the wall.

Unfortunately, that would also mean I'd have to cut a hole in the granite for a not-so-appealing air gap.

Neither is a great option.



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There are plenty of choices when it comes to water alarms these days. Some are even smart, so that should not be a deterrent.

The water sensor would be another viable option to avoid having all the rework to the kitchen. I should be able to find one with a set of dry contacts to pull into the alarm system as a separate zone.