Tankless install and re-route fixture supply lines

dgeistJuly 24, 2014

I am in the planning/prep stages of converting from a tank to tankless water heater. The new unit will be wall-mounted just to the right and below the capped-off copper trap in the picture. I plan on extending the 3/4" lines at the top center over to that area for hot and cold connections (blue and red lines starting from top center).

I'd also like to move the existing fixture supplies over to that new section of trunk (i.e. closer to the outside wall, new lines in blue and red. Lines to be removed in black). Will moving the branching points over there impact impact flow much vs where they are now? I'd like the middle of the room to have a few joints and valves as possible for when I put in some finished spaces later.

FYI, I'm in Atlanta (temperate) and I'll be blocking and sealing the rim joists with foam at the same time, along with installing a new frost-free sillcock. So..minimal freeze consideration necessary.

Is my reasoning sound here? Are there any gotchas with pipe and shutoff placement that I need to consider?


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Nope, I think you are good.

Do you have adequate gas supply to the new heater? will also need outlet and drain if you are using condensing heater.

    Bookmark   July 24, 2014 at 2:23PM
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Hi, Jake. The gas rating is 199k BTUh, and I'm planning on having either a licensed mechanical contractor or plumber do the black-pipe and gas termination. Also, I need a meter upgrade and my local utility won't dispatch for the (free) service without the signature of a licensed contractor (even with the right documentation and calculations present...).

I have a standard 15A outlet reachable for now and plan to hard-wire it on a new dedicated circuit later when I do some electrical upgrades. My city is okay with either.

As for the drain, there's a sump for the perimeter drain tile just to the right of the waste stack. The tankless has an internal consumable neutralizer upstream of the drain, so I think the PH will be fine to plumb to the sump. I intend to plumb the TPR valve to the same place with a hard line since the outside grade is above the install height. The current tank has the TPR overflow going UP and out to the back yard (front and center in the picture). I thought the output had to be below the TPR valve by most code, but if not, I could always reuse the existing 3/4" line going out through the concrete block.


    Bookmark   July 24, 2014 at 3:46PM
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Hey Dan,

Just a couple of tips: Your existing outlet is fine... you don't want to hardwire it and you don't need to put on a dedicated circuit. The power draw is very minimal (100 watts if freeze protection is on, I think). The plug provides a disconnect means - otherwise if you hardwire you have to provide a disconnect within sight of the unit so that you can service it. I did install an outlet right next to my heater - but not on a dedicated circuit.

The code on the TPR discharge is that the end of it must be visible ( in addition to not being reduced or restricted). It sounds like you will be fine... but just a heads up.

Here is a link that might be useful: TPR discharge piping

    Bookmark   July 25, 2014 at 9:43AM
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On the power, I'm planning on putting in a small panel of "battery-backed" circuits for the house, to which I want the tankless connected so we have hot showers if there's a power outage. I know the current draw is very low. I've run them off computer UPSs before for this very reason. The outlet or hard-wire would have a switch at the appliance location either way I wire it, but that can be a decision for another day.

Thanks for the link. #5 definitely confirms that the current TPR drain line does NOT comply (pretty sure it's not going to drain by gravity 3 feet uphill...)


    Bookmark   July 25, 2014 at 12:26PM
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#6 makes it a no-no also... guess Jake-TWD didn't read his own link.

UPC *used* to be (still is?) very explicit about TPR piping, i.e. all segments have minimum 1/4-in-12 DOWN slope, no more than 360 degrees total bends/ells, etc., the INTENT being that the slightest volume of discharge be immediately evident at the discharge/air-gap.

Do hope your tankless adventure doesn't get too... adventurous. There's so much to be said for ye olde drama-free highly-debugged NON-electronic zero-rotating-parts long-lasting INexpensive gas-fired conventional WH ;')

    Bookmark   July 28, 2014 at 5:10PM
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Yes, Fixizin, I did read my own link.

He was intending to send the TPR discharge to the sump.
I don't know the exact layout of that... that's why I sent him the link.

Fixizin, your conventional gas water heater isn't that great. It sends about 35 cents of every dollar spent on hot water out the flue. They typically lasts 12-15 years (because you can't clean them) and they take two guys to wrestle them out of the basement.

What's more - you typically have a flue that's part of that initial cost for conventional gas tank. Upkeep of that flue and protrusion through the roof is another cost (I've seen a lot of corroded to the point of perforation water heater vents as well as leaky roof boots). With a condensing tankless, you have a PVC pipe through the wall in most cases and can use an outside air intake as well.

I have an older house - I changed to a smaller 95% furnace and a tankless water heater - and didn't need to change gas service. I did need to run about 30 ft of 3/4" gas line.

People should know all the costs before committing to tankless, but your FUD isn't helpful.

    Bookmark   July 29, 2014 at 9:53AM
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Your lay-out looks fine. A consideration however is pipe lay-out to the house fixtures. Keep in mind that the cross sectional area of 1/2, 3/4 & 1" pipe is .19, .44 & .77 sq in. Those numbers equate to vol of water to be moved before delivery of hot. In some situations I've run a dedicated 1/2" pipe to the kitchen so I basically by-passed the main 3/4" trunk. My point is to look at your water heater placement as a component in your "system". Where is the best location for the water heater for your on-going comfort and conservation of both energy and water. Don't be afraid to move the water heater upstairs if you can vent it and it improves the system.

I would strongly suggest as you develop your finished basement spaces that you not Sheetrock the ceiling. That basement ceiling is your mechanical area. Put in a drop ceiling. You will still be able to access everything. I am having this issue at my daughters house. The PO rocked the basement and garage and I now have to trash all of it.

Oh, one other thing. Install a 3/4" pex recirc line. You may not need/use it, but if you decide to it is there. Easy money when it is open. Not so when done. Your plumber will likely suggest 1/2", but depending upon the recirc system you install you will have much better operation with the 3/4".

    Bookmark   July 29, 2014 at 11:46AM
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This isn't my first tankless rodeo, so I agree (and have experience with) all the points jake mentioned. I choose to ignore the troll.

Jack, I get what you're saying to keep diameter as small as needed to improve delivery speed. The kitchen is (literally) directly above the install location, and I intend on what amounts to copper 1/2" "home runs" to the extended 3/4" trunk for everything there. Getting 199k BTU/h upstairs and re-plumbing everything is not really worth the small decrease in delivery time that it would translate to. Perhaps if it were new construction.

I'm not sure what you mean about putting in a PEX recirc loop... I'm plumbing this part all with copper (may do home-run PEX down the road when I remodel some bathrooms, but not yet).

    Bookmark   July 29, 2014 at 12:10PM
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His point was that you can install a return loop for recirc now, while everything is open. You don't have to hook it up, but it's there if you decide you want it later. I think he was saying to use PEX because it's cheap and easy - esp if you end up not using it.

BTW: I did replace my 3/4 run to my kitchen with 1/2" just to cut down on wait time.

Also, be sure to insulate all of your hot water pipes - it makes a big difference in the amount of time water stays warm between uses (cuts wait time for hot water) It also cuts heat loss in the event you do decide to install recirc.

    Bookmark   July 29, 2014 at 1:59PM
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Here's the finished install, BTW. You can see how I removed all the old distribution and appliance connections and plumbed in the new. I've yet to remove the old water heater, but that's a minor issue.


    Bookmark   December 28, 2014 at 1:09PM
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