Newbe supplemental tankless questions...

Discussion in 'Tankless Water Heater Forum' started by wilobe, Oct 1, 2011.

  1. wilobe

    wilobe New Member

    Messages:
    10
    Location:
    Central Florida
    We’re planning an extension to our master bath, and would appreciate input on adding an electric tankless WH as supplement to our existing plumbing within that expansion. Current configuration has a single MB sink at the outside (framed) wall that we intend to remove for the extension. Existing plumbing comes up out of the slab into that wall, so we understand some of that slab will have to be demoed/replaced to connect to that location for the hot/cold water source to the expansion. Planned addition includes a double shower, two sinks and possibly a tub. Our intent is to have the tankless heat the hot water line (cold water slug?) between the natural gas tanked WH, (about 40 ft away in the garage) and the master bath.

    Questions:

    1. As we haven’t opened that wall as of yet (thus suspect ½†supply at that existing sink) , is it reasonable to reroute that existing hot water supply line (under the future slab extension) up thru the master bath electric tankless to the new shower heads and sinks?
    2. Are we correct in assuming that since the tankless will only be a supplement at the remote location (master bath), that a smaller (less wattage) unit will work well?
    3. Is there a need for a water filter at the input to an electric tankless WH?
    4. As we eventually intend to convert the garage gas WH to tankless, are there any issues we need to be aware of?

    Thank You, in advance for your expertise,
    Jerry
  2. Surfing Plumber

    Surfing Plumber New Member

    Messages:
    10
    Location:
    Orange County, CA
    Electric tankless is not efficient and you will NOT reach your desired shower temperature. I tried to install an electric tankless one time and the amount of work: subcontract an electrician to upgrade the panel and running 3 220V plugs was ridiculous!! That is like running 3 electric clothes dryers simultaneously!! I think you should re-think about propane powered tankless. Its a lot more efficient and you will definitely be more happy with it.
  3. wilobe

    wilobe New Member

    Messages:
    10
    Location:
    Central Florida
    Thank You for your reply. I have been rethinking the issue and reading more on this forum. We were hoping to mitigate the cold water slug at the far end of the line (master bath) by running it, in series, through an electric tankless within the new expansion. It looks like we’ll need to really weigh the cost vs gain tradeoff. We were not aware of the apparent problems with the electric tankless units.

    Any additional comments on converting the main storage type gas WH to tankless in the future?
  4. johnjh2o1

    johnjh2o1 Plumbing Contractor for 49 years

    Messages:
    1,142
    Location:
    South*East
    Electric tankless heaters have a flow restrictor to allow the water to heat. You will not be happy with the volume of water you will get in your DBL shower.

    John
  5. Dana

    Dana In the trades

    Messages:
    2,785
    Location:
    01609
    If you have only 40-50' of 3/4" plumbing between the gas-fired tank and the new showers, etc you're talking about only about a gallon of water. A tiny 4-8 gallon electric tank heater located at expansion in series with the hot water feed from the main tank would provide sufficient dilution for the tepid-water in the 50' of plumbing that showering would be fine, and on short-draws there wouldn't be any wait. It needn't be fast-recovery or anything- something that works on a 15amp service would be fine. The cost of upgrading the electric power for a sufficiently high flow tankless just to heat up that gallon of water 1-3x per day is daunting- would take about 900-1500 years to pay off on utility savings over a tiny tank solution. Displacing a gallon of 125F water in the local 4-gallon tank with a gallon of 70F water from the intervening plumbing between the tanks only drops the temp to ~111F, which is still above the typical ~104-108F showering temps. Don't go smaller than 4 gallons or you'd have to crank up the temp on the mini-tank considerably. If it's half-inch feed it's roughly half the volume and you'd be OK with 3 gallons of local tank.

    Replacing the gas fired tank with a tankless has some payback on efficiency if it's propane, not so much if it's natural gas (unless it's heavily subsidized by the local utility). With a gas fired tankless you get the convenience of never running out of hot water, but your peak flow rates will be lower than that of a tank. You also buy back a few square feet of floor space in the garage (especially if you mount it outdoors, which is fine in FL, but not in places with more serious freeze potential.) A condensing gas-fired tank would have higher peak flow and is about as efficient as a tankless, but in most cases it would provide fewer first-hour gallons than a tankless.
  6. wilobe

    wilobe New Member

    Messages:
    10
    Location:
    Central Florida
    Again, Thank You for your reply. Sounds like a tankless will be cost prohibitive, especially with respect to electrical upgrade requirements. I must admit I never even thought about a small storage unit within the expanded MB area. I really like the idea of a single 120 volt hookup as our electrical panel is also about 40’ from the future expansion area. Preliminary search results seem to indicate that an in-line point-of-use (?) wall mount mini-tank may be just what we need. Any specific brand recommendations?
    As stated in our initial post, we haven’t opened that wall as of yet (thus suspect ½” supply at that existing sink) , is it reasonable to reroute that existing hot water supply line (under the future slab extension) up thru this new in-line electric mini-tank to the new double shower? What kind of flow restriction should I expect? Also since the wall where these current sink supply lines penetrate the slab will be removed, to provide walkway access to the new area, will it be OK to have the connection joints below the slab for the line to the new devices? Reason I’m asking is cause I believe there may be access to a ¾” above slab connection in another wall about 5” away – obviously that will require more slab cutting. Your inputs appreciated.......
  7. Dana

    Dana In the trades

    Messages:
    2,785
    Location:
    01609
    It's reasonable to route the supply anywhere- just be sure to insulate it with at least 5/8", and preferably 3/4" wall-thickness closed cell foam pipe insulation. Uninsulated, if embedded in concrete or soil the heat losses will be many times that of being simply suspended in air (uninsulated.) Even where it's only surrounded by air insulating the pipe to R4+ is cost-effective, and much easier to do as you go along rather than retrofit. The stuff sold at box stores is typically only 3/8" goods. The fatter stuff may need to be sourced online, at plumbing supply distributors, or at Graingers.

    If run only 1/2" pipe with lots of twists & turns you may run into sufficient water pressure drop to limit flow with more than 1 shower running, but usually not. It depends on the total length, your water pressure, and the number of bends (every sharp turn in half-inch is like adding 3.5' of length to the pipe from a pressure drop point of view.) If you go to 3/4" you get better flow, but have roughly twice volume of tepid water in the pipe, meaning you'd need to go bigger on the mini-tank. Bucket-test the existing half-inch feed- if you can get 5+ gallons per minute out of it you're going to be fine unless you put real gushers for shower-heads or have side-sprays or other high flow aspects to the showers.

    Decide where you're going to run the pipe and measure the length and decide on diameter before picking the tank. You need to know the volume first to get it right. The minimum size of the tank that works ultimately determines the available options.
  8. wilobe

    wilobe New Member

    Messages:
    10
    Location:
    Central Florida
    Thanks for the insulation tip, we will incorporate. As we’re still months out, we can’t open that wall right now to connect directly to the 1/2” pipe, however we did a quicky check-see at the single-piece faucet (aerator insert removed), 3/8” (?) shut-off valve / rigid supply tube – and consistently got about 4 GPM. So because of the 3/8” restriction, would it be reasonable to assume that the GPM (before the restriction) will probably be at least 5 GPM? From that connection point (below the slab) it should be a straight run (about 8’) then up into the storage WH. Incidentally, we did a pressure check at the outside spigots, all three were about 72 PSI.
    We’re now of the opinion that we’ll need to read up on in-line point-of-use wall mount mini-tanks – 4 or more gal, ½ input, single 120/120 volt. Any BRAND recommendation????
  9. wilobe

    wilobe New Member

    Messages:
    10
    Location:
    Central Florida
    We're currently attempting to develop a budgetary estimate for our overall project/MB expansion. Part of the communications with two different plumbers was that, in their opinion, we should install a hot water recirculation pump/system as opposed to the supplemental MB mini-tank we’ve been discussing above. So we’ve searched/read about recalculating systems on this site. From what we understand/believe a dedicated return, because of the slab, is not particle. Still don’t quite understand the hook-up utilizing the cold water lines as the return; but....

    Questions:
    1) Wouldn’t a cold water line draw, anywhere in house (including outside bibs), siphon hot water out of the main storage tank?

    2) Anybody care to hazard a guess for an insulation cost? (utilizing cold water line for the return)
  10. Dana

    Dana In the trades

    Messages:
    2,785
    Location:
    01609
    When you open a cold water tap the water flows from the point of highest pressure, which is where the mains come in from the street to the point of lowest pressure, the tap. (It would take quite a feat of plumbing-idiocy to have the cold water for the rest of the house plumbed in series with the HW tank, but I'm sure it's been done. :) ). With a recirculation pump there is the issue of tepid water at some intermediate temperature being abandoned in the section of cold line being used as the return after the pump stops, and the cold taps on that line will sometimes not be cold, but rather luke-warm.

    With a recirculation system with controls set up to keep the hot water always available at the remote bathroom the standby loss is considerable, even with insulated pipes. Even the timer operated versions that turn off overnight waste more energy than a mini-tank. To avoid that loss there are some that require manually hitting a switch to call the hot water, and the pump kicks off via a local temperature sensor control. Recirculation systems cost more than mini-tanks up front too.

    Insulation costs vary bulk from internet sources, or at some plumbing supply outlets it's somewhat cheaper than this.

    http://www.grainger.com/Grainger/INSULTUBE-Pipe-Insulation-3F410?Pid=search

    http://www.grainger.com/Grainger/NOMACO-KFLEX-Pipe-Fitting-Insulation-4NRF2?cm_sp=IO-_-IDP-_-BTM_BTB05209020&cm_vc=IDPBBZ2

    http://www.grainger.com/Grainger/NOMACO-KFLEX-Pipe-Fitting-Insulation-4NPY8?Pid=search

    http://www.grainger.com/Grainger/NOMACO-KFLEX-Pipe-Fitting-Insulation-4NRA5?cm_sp=IO-_-IDP-_-RR_VTV70300505&cm_vc=IDPRRZ1

    Figure on something like a buck a foot for the straight sections, but don't forget to insulate the Ls & Ts too (either with the pre-formed purpose-made goods, or 1-part spray foam such as Dow GoodStuff, etc.) Average may be closer to buck and a half per foot, installed by pro, not DIY.

    Or maybe you meant "installation cost", for a recirculation system (and not "insulation cost", thus)?? Too many variables to say- it depends on the equipment chosen, the relative ease of installation, and plumber's rates in your area. Get some quotes. It's comparable overall to the mini-tank solution. The cost for the pumps themselves runs similar money to 5-8 gallon 120V tanks.

    http://www.******.com/Reliance-6-6-SOMS-563661836/prices-html

    http://www.amazon.com/dp/B003DR2EX8/ref=asc_df_B003DR2EX81747492?smid=ACP9B1ET1BHYS&tag=******usmp0403817-20&linkCode=asn&creative=395105&creativeASIN=B003DR2EX8

    http://www.amazon.com/Watts-500800-Premier-Water-Recirculation/dp/B000E78XHG/ref=sr_1_1?s=hi&ie=UTF8&qid=1319655138&sr=1-1

    Installation ease of tank vs. pump will vary with the particulars.
  11. wilobe

    wilobe New Member

    Messages:
    10
    Location:
    Central Florida
    Trade-off assistance please

    Thanks for the thorough "insulation cost" info Dana, I'm sure it will be very useful during our plumbing rough-in. Right now, I'm embarrassed as my brain/finger coordination, or lack there of, is exposed. You were correct, I did mean to ask about "installation costs" - Thank You! I could be wrong, again, but it seems to me that installing a nondedicated-return recirc set-up, as a retrofit, into our existing slabed home would be more beneficial to the Plumber than to us.

    That said, I think we're back to incorporating an electric storage tank in our MB addition. Now the trade-off, I think, is between a small supplemental booster tank (probably 2.5 to 4 Gal) feed by a 1/2" line coming from the main WH, OR a bigger stand-alone tank (6 to 10 Gal) feed by the (colder) 3/4" line from street. It seems, to us, that the initial cost (purchase and installation) is nearly a wash between the two.
    Inupt Info: 2 adults / Central Florida / 2 individual 1/2" shower controller valves / 2, 2.5 GPM shower heads.


    Questions / Requested Advice:

    1) Since the small booster tank would only really be utilized to heat the initial cold water slug, from the main WH at the start of a draw, and maintaining the desired storage temp between draws, wouldn't the expected operating cost be quite low?

    2) Any estimate of the street feed stand-alone operating cost as compared to the above smaller booster unit arrangement?

    3) Would the increased water pressure/volume, at the shower heads, from the stand-alone 3/4" street feed, really be worth the (I think) increased cost difference as compared to the small booster 1/2" main WH feed?

    4) Considering the above, would we better off just continuing to tolerate the approx. 1 minute cold water delay when turning on the hot water in the master bath?
  12. wilobe

    wilobe New Member

    Messages:
    10
    Location:
    Central Florida
    Sounds like we'll be continuing to tolerate the approx. 1 minute cold water delay when turning on the hot water in the master bath. Its been that way since the house was build, just thought that with this addition it would be nice to correct it.
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