This is the first time I’ve ever seen the water pipes for the tankless water heater installed this way on a new construction. Usually, the hot and cold water pipes are completely separate, but at this house they are connected by the valve in the middle. There is also typically a separate shut off valve on the cold water pipe right after it comes out of the drywall, but none here. This is a rinnai RE180i BTW. Not really sure what they are trying to do here? Any ideas?
Looks like a bypass valve.
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Agree, but not sure why.
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Can you do the flush or a full service without interrupting water in the home? Yes, I realize you’d get no hot.
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A poor man’s mixing valve? Not sure why you would do it on a tankless, but you never know.
Or part of a recirculating system? 
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Looks like a system that does space heating plus domestic, with one tankless, where that bypass is used. Also looks like a relatively small gas line for tankless. More pictures?
Images further back please, Yu.
Thought about that too…but couldn’t continue down that line of thinking because what are we really bypassing here though? yea its odd.
yea…normally you get no water coming out on the hot side if you shut water off just to the water heater for service. Now you get cold water coming out the hot side for the plumbing in the house? Not sure that really helps that much, unless people like taking cold showers?
Nope, not that fancy. Only a single tankless for the hot water in the house. House has a gas furnace/electric AC for heating/cooling purposes.
Nope, no recirculating system no pump. No water softener. That’s why it makes no sense to me.
This is as far as I got in the garage. Left of the water heater is the main water shut off to the house, PRV, and shut off for exterior hose bibs.
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Thank you. Much appreciated.
The bypass is probably built in at the request of the client to winterize the plumbing system.
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I have a tank less in my home, I assume it is for flushing out the heater without shutting down the whole house and just flushing the unit.
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Where does that condensate line go? Remember condensate eats through everything, but plants like it.
That’s just the pressure relief pipe run to the floor. Not a condensing unit
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Looks good from here.
Where do you see a condensate line?
The OP stated that’s a TPR instead. I had thought condensate, based purely on the type of pipe used. Thus my question switches to the usual technical concerns about TPR in plastic.
What’s your concern?
It’s not my concern, though it commonly comes up here. The plastic pipe is not rated for the temperature of the potential outflow (212F +) from a malfunctioning water heater.
It is CPVC OK
What say you @mwilles
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