is 1" id enough?

Discussion in 'Tankless Water Heater Forum' started by tarjan, Apr 21, 2012.

  1. tarjan

    tarjan New Member

    Messages:
    9
    Location:
    VA
    Drip... Drip... Drip. I hear it somewhere, but cannot figure out where. Not in the kitchen, not in the bathroom. Where?

    Dog? Nope, he is asleep.

    Shoot, I hear it coming from the utility room. Venture in and I find water in front of the furnace. "That's not good at all" I think. Then it gets worse, the water isn't coming from the ac condensate line like I was expecting. Backtrace and it is coming from the top of my hot water heater and draining down the outside of the furnace/blower to the floor drain. DARN, so after 12 years and one month my Ruud 75 gallon unit is toast.

    So now I have to replace it. I have a whirlpool tub, and the 50g tanks won't cover it. Do I want to get another 75 gallon tank OR do I want to get a tankless unit? If I get it installed before the end of the month there is a rebate available for high efficiency tankless. I'm thinking tankless, space savings and no longer using inside air for combusion since my gf and I are extremely allergy sensitive. Limiting drafts would help.

    The condensing units are running around 1400-1600 unit cost, add in the service valves and PVC venting and it should be about 1800 total materials cost (sans copper and gas line of course).

    That leads me to the real question. After calling a few places and getting price quotes from 3k to 6k for the install, the one thing that keeps popping up is the gas line. Mine is 1.3"OD (measured with calipers) which should equate to 1" ID from the meter into the house. Goes up about 6' in about 5, turns 90 for 5, turns 90 for 5 and hits a t. One end goes to my gas oven, the other end goes to the utility room about 10' either way.

    In the utility room it goes from 1" to 3/4" at a t, one side to the furnace and the other to my existing HWH.

    Is this enough information to say if the 1" pipe is enough? (199k BTU)

    Otherwise the install is bone simple. I have power in there, the floor drain is easy to get to and the utility room has an exterior wall. Go up high enough and you can cut through the siding and have a simple exit. No features, windows, or anything else nearby. Gas line on the other hand is in the ceiling and the basement is finished. That would add thousands to the cost :(

    (was thinking rinnai 98i condensing or rheem 95dvn condensing since that's what the vendor has. )

    Gas appliances are furnace, range and oven and gas fireplace.

    The help is MUCH appreciated.
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,949
    Location:
    New England
    This website may help you figure it out http://www.engineeringtoolbox.com/natural-gas-pipe-sizing-d_826.html. You'd probably want to keep the line 1" all the way to the tankless, but if the furnace and the tankless were both on at the same time, it will happen, you have to take all of those things into consideration. I didn't run your situation, you may need to upgrade your entire gas service. Starving the appliance for fuel would be a big hit to performance.

    Also, VA probably doesn't have super cold incoming winter water temps, but it might, depending on how the piping is run, and the weather. A deep well could be super cold all year long, rather than a municipal supply in the middle of winter. The tankless units produce lower temp hot water as you reach the max flow. Most can raise the incoming water temp around 50-70 degrees at max flow. You need to read the spec sheet VERY carefully to determine if you're going to get decent flow to fill a big tub in a timely manner. With a tank, it has potentially hours to recover...with a tankless, it's doing it upon demand, and the only way to get more hot water is to use a bigger flame or slow it down to maintain the desired temperature rise.

    So, the decision is yours. You probably haven't done anything to the WH in those 12-years...you will not get away with that on a tankless which may require at least annual descaling (depends on your water chemistry and use). Think teapot...eventually, you have to clean out the deposits. Maybe a quart or two a day. Now, amplify that by a factor of 100's (but, the water doesn't get as hot, so you don't get as much per gallon heated). You see what I mean...those deposits limit heat transfer and flow, they need to be removed on a regular basis. If you're really lucky, you can go awhile, but you will need to do it eventually.
  3. saphman

    saphman New Member

    Messages:
    19
    Location:
    Northwest Florida
    I Agree with jadnashua. The gas line is a critical factor in performance of the tankless units. I just installed the Paloma phh 32dvn which is a rheem unit identical to the model you quote. It sounds like you are running 1/2 psi gas pressure with the size of the incoming line you have. Do your research and check the natural gas tables on line size and CFH. This all relates to BTU's and you will need to supply that heater with 200,000 of them RELIABLY, or you will get error codes and little or no hot water.

    You might also ask your gas supplier about upsizing your gas meter and or pressure. Many newer systems are running 2 psi gas pressure. With that amount of inlet pressure you will have no problem using a 3/4 " gas line to that unit. In that case you would need regulators for your gas appliances.

    Having just completed my installation, I cannot emphasize enough: Do your research!!!! Installing one of these takes careful planning and reading. There is lots of good information on this site.
  4. tarjan

    tarjan New Member

    Messages:
    9
    Location:
    VA
    FYI: I actually did try to take care of the WH :) . Draining it once a year to clean out the sediment etc. A 75 gallon tank takes hours to drain. I did not replace the anode since it was listed as non-replaceable, but didn't figure out till later that is not quite true.

    The idea of running some vinegar through the system is no big deal, I'll just use the same on my espresso machine when I am done since I do that yearly as well :)

    The real issue is still the gas line. I don't think I have a 2psi system based on the fact I don't see anything that looks like a regulator in the line at my gas appliances. Just a normal shutoff at each point. I would imagine in my situation that would be a much cheaper solution than ripping out the pipe and replacing.

    That leads me to the table in Jim's message. To read it do you add all of the pipe lengths up in the house and compare or is it the length from the meter to the appliance and use the total CF/BTU requirements of the house? Looking at some sites it seems to be the longest length seen in the system (which this would be,) and not total length of each leg.

    If the latter is this case I would estimate 30ft from the meter to the spot where the TWH would be, which would give me a figure of 320CFH conservatively. Realistically it is more like 27ft. Either way, 320 doesn't give me much leeway because adding my appliance up I get 326. (180 TWH, 64 furnace, 60 oven/range (single oven 4 burners), and 22 for fireplace. Drier is electric)

    Now the chances of me ever turning on all the burners on my stove and my oven on full AND having my fire place running AND have the furnace on are nill. But I definitely could have a burner or two on medium and the oven on with the furnace and needing hot water.

    So based on this, if I am understanding everything correctly, I *may* be able to do it safely, but it is sufficiently tight that I need to have a professional bless it no matter what. Reasonable assessment?

    BTW: water is municipal, temp in the winter is 45 or so and summer is probably 55-60. One sheet shows the water temp to be 58 in the summer, but I figure it is less than that, who knows. So I would need about a 60deg gain and if I get the 9.8gpm unit that comes out to be about 6gpm max to maintain the 60deg gain which i think should be ok, though I wouldn't be able to run other things at the same time.
  5. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,949
    Location:
    New England
    Each elbow creates resistance, and the effective length of the pipe gets shorter. IOW, if you figured it on a straight pipe and were minimal, throw in a bunch of changes of direction and you now aren't.
  6. tarjan

    tarjan New Member

    Messages:
    9
    Location:
    VA
    Gotcha. So it may be unlikely it will work without an upgrade and I definitely need a pro to help me out.

    Thanks for the help Jim! Hopefully I can have someone out Monday to help me decide on which direction to go, but at least now I have the information I need to make sure it is going to be done right.
  7. Dana

    Dana In the trades

    Messages:
    2,814
    Location:
    01609
    The 50 gallon Vertex 100 condensing tank with the 100K burner delivers 160 first-hour gallon- better performance than most 75gallon standard-efficiency tanks with ~75K burners, and would be far less likely to run into gas supply issues than with a 199KBTU/hr Rinnai.

    Unit cost is ~$2KUSD, but should be pretty much a drop-in for the 75 gallon tank.

    What's the burner size on the leaking Ruud, and was it able to fill the whirlpool without running tepid at the end?
  8. tarjan

    tarjan New Member

    Messages:
    9
    Location:
    VA
    It was 75k btu and yes it could when set at 135-140deg winter, 125 summer. Colder than that and it could be an issue.

    A few high end 50g tanks were used during the construction of the homes but all were eventually replaced with 75g tanks when they were found to not work well enough for the two person soaking/whirlpool tubs, though they were not condensing units. They would gather people while the demo houses were under construction and those show houses would run out of hot water 75% of the way through during the demos (only one demo a day). Obviously that wouldn't work so they said "we are only temporarily using these and will put in larger tanks" hence 75g and 60(summer)-75 (estimated winter)/month bills.

    So here is where I am, the first company came out and we went over the details. No way to run on existing line, like expected. Two answers are either to upgrade to 2psi as is, which requires regulators at each appliance (difficult with the fireplace, no way to make it fit vertically) or to do a split system and run a second pipe next to the house in a pvc sheath close to the ground. Then up and in at the right location. I could plant some bushes to hide it very easily.

    Cost of either solution to the gas line sizing would be about the same and the later would not cause a drywall kerfuffle, nor would it require a 24hr whole system retest for the inspector, but it is visible.

    Total between 3600-4000 installed, rinnai rc98i. 300 dollar rebate being offered by my local utility for high efficiency tankless units.

    I have a few more quotes coming, but initial quotes seem to be fairly close though we will see.

    The condensing unit is tempting, but the reality is 3600 would give me twice the ownership length in theory... it could pay itself off if it lasts darn near forever. :) Unfortunately it means no new carpet for another year.
  9. Dana

    Dana In the trades

    Messages:
    2,814
    Location:
    01609
    The 75K burner Ruud you've been living with is only good for ~140-150 first-hour gallons.

    Condensing tank heaters have fewer issues than tankless, since they're fundamentally simpler beasts (no flow sensing or modulating fire/temperature regulation to worry about.) It's probably worth at least getting the Vertex 100 quoted, since it probably won't need new gas lines, and will likely work at least as well as the 75 gallon tanks.

    Initial tub-filling rates would be higher than you'd get with a 199K tankless, but depending on volume you may have to throttle back toward the end. The BTU/hr output of the 75K burner on the Rheem is only 60KBTU/hr- enough for about a 2gpm flow of 110F water forever at typical VA incoming water temps, whereas the 100K burner on the Vertex 100 is good for more than 3 gpm continuously. What you'd get with the condensing tank is better than 50% more heat output for only a 33% increase in burner size.

    There's rarely a real "payoff" with a condensing water heater when the source fuel is natural gas- it's a much easier financial argument with propane.
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