Smallest allowable tank size?

Discussion in 'Water Heater Forum, Tanks' started by kcodyjr, Nov 18, 2013.

  1. kcodyjr

    kcodyjr New Member

    Messages:
    103
    Location:
    Chelmsford, MA
    I bought a 1971 12x60 mobile home that the seller had just replumbed. As it turned out, they were repairing a rusted out main, but I had to learn that from the next door neighbor after i bought it.

    Their replumb included a 30 gallon Whirlpool electric tank, but didn't include repairing the rotten subfloor the thing was sitting on. I was able to grab the top of the tank and swing it around by about 6 inches. I've ripped it all apart and discovered the weight of it was carried on only one 2x4, laying on its side, and the metal outriggers below that aren't particularly wide in that outer 2 feet.

    I'm not convinced that any amount of reinforcement can make that safe, it's only a 100A service so an electric tankless is out, and there's no gas in the street, and leasing a propane tank would be prohibitively expensive just to run a water heater.

    It's only my two year old daughter and I, so Army-style showers would be only a minor inconvenience. She gets shallow baths.

    How small a tank have people gone with in this situation?
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,015
    Location:
    New England
    What is the wattage on the existing tank? A larger tank doesn't necessarily mean higher wattage, it just means it takes longer to recover. Depending on what else is in the mobile home, there are bigger tanks that use lower wattage elements, and would be no worse than what's there.

    Any water heater needs a solid floor, and obviously, a larger tank may become a bigger issue, but it sounds like this needs to be addressed, regardless.
  3. kcodyjr

    kcodyjr New Member

    Messages:
    103
    Location:
    Chelmsford, MA
    I can't see the spec plate at the moment - it's disconnected and jammed into the back of the master bedroom closet, which its normal space abuts - but it's fed by a 30A 240V circuit; at 80% loading, maximum possible wattage would be 5760.

    The performance of the tank isn't an issue, it's the sheer weight of the thing. Guessing 70 for the tank plus 30*7=210 for the water, 280lbs.

    If I do go with the small tank strategy, a similar power rating would be good. I'd rather not rewire for 110, and the faster recovery might be sort of like a consolation prize. Maybe even fast enough to reheat while I soap up, but that's probably too much to hope for...

    Whatever I do, it'll be feeding a shower, a kitchen sink, and a double (??!!) bathroom sink. No laundry, no dishwasher. Commode is on cold.
  4. Reach4

    Reach4 Active Member

    Messages:
    2,251
    Location:
    IL
    They do have small on-demand water heaters that run off of 240 volt 30 amp, or even smaller, circuit.

    Those are more efficient for occasional use than heavy use, because they don't waste power keeping the water hot all of the time. On the other hand, they may be more trouble than they are worth. We recently read of one on-demand heater maker who's warranty was invalid if you used the unit with water with more than 7 grains of hardness! It sounded pretty unreasonable to me.
  5. kcodyjr

    kcodyjr New Member

    Messages:
    103
    Location:
    Chelmsford, MA
    All else being equal, I'd rather go with tankless, but I have to question how effective a 6 kilowatt unit would be in Massachusetts.

    I'd expect town water temperatures to occasionally be just above freezing, mid-40's average during snowplow season.
  6. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,015
    Location:
    New England
    I do not know what the code allows on this, but you may be able to put something like an a/c compressor pad on the ground beneath, something like this: http://www.hamiltonhomeproducts.com/c/35/condenser-pads?orderby=15, then, maybe build a platform on top of it to support the subflooring underneath.

    You'd have to check with the local building inspector. Maybe someone else will have a better solution.
  7. kcodyjr

    kcodyjr New Member

    Messages:
    103
    Location:
    Chelmsford, MA
    The trailer is standing on cinderblock stacks - notice I didn't call them piers. The whole thing is prone to shifting and settling, and so would any attempt to support the heater from the ground. In fact, I think that heater is the reason I just had to rebuild that particular stack. The bottom two cinderblocks had sank fully halfway into the dirt.

    Unfortunately, I don't think effective anything can be done about that. It's leased land. I can stack all the cinderblocks I want, but no digging and no probably no mortaring either.

    Just to cover the bases, what kind of $$ would I be talking about to bring in propane?
  8. Reach4

    Reach4 Active Member

    Messages:
    2,251
    Location:
    IL
    Because the water supply is well below ground, I expect the water temperature of the flowing water to not vary all that much winter vs summer.

    However I see the http://www.stiebel-eltron-usa.com/mini.html heaters cannot do much a heat rise. Their rate to detect flow and turn on seems to be too insensitive to be worthwhile. So scratch that.
  9. kcodyjr

    kcodyjr New Member

    Messages:
    103
    Location:
    Chelmsford, MA
    Not just the temperature rise; those minis don't have much flow capacity even at the rise they're rated for. Stiebel's website says I should be using the Tempra 20. At 6kw, I might as well hold a cigarette lighter under the pipe. However, the 20 would take literally every ampere I've got coming in. Hot shower plus one lightbulb equals blown main; just add profanity when the water is suddenly back to street temperature.

    I could run the 15, just barely, though there might be issues if the furnace and fridge kicked on. I really doubt 12 would cut it.

    I'm still waiting to hear back from the power company about what's coming in. The meters look 200A capable, but I have no way to tell what the rating is on the cable running from there to the connection drop, or on the drop itself. I know I'd have to do a panel and feeder.
  10. Reach4

    Reach4 Active Member

    Messages:
    2,251
    Location:
    IL
    240*100amps is 24 kW. Not that you can do that, but you could approach about 80% of that. What amperage 240 V breaker was the old heavy water heater wired to?
    Last edited: Nov 18, 2013
  11. kcodyjr

    kcodyjr New Member

    Messages:
    103
    Location:
    Chelmsford, MA
    It was wired (poorly) to a 2-wire plus ground 12ga cable and a 30A breaker.

    Also, I believe you've got a decimal error there. 240V x 100A = 24000W = 24kW.

    I just sent Stiebel Eltron an email asking if the Tempra 24 can be derated to run on one element while waiting for a service upgrade. Seems like nobody's chiming in with success stories of using a small tank, so going with a weak tankless through the winter might be the only option.
  12. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,015
    Location:
    New England
    Those platforms are designed to hold an a/c condenser unit, often up to 300+ pounds with NO extra anything while sitting on the ground. The only thing you have to do is to level the ground, set it in place, and it acts as a stable platform to distribute the weight. They come in different sizes. It should easily hold a WH. If you built a platform on it to the level of the bottom of your subfloor, then all of the weight would be transferred to the ground, and essentially none on the subfloor. But, I do not know if it would pass code for this application. It might, and would be cheap and easy to then rehook up the WH you have. Worst case, you dig a little soil out and put in some gravel or crushed stone first.

    FWIW, a 12g wire on a 30A circuit is NOT sufficient! If the WH doesn't need that much to run (you'd have to look either at the data plate or find the spec sheet), you might be able to drop the CB to 20A, the max a 12g wire can support, or you'd need to run a new wire to support the 30A breaker.
  13. ImOld

    ImOld New Member

    Messages:
    73
    Location:
    In the rumble seat
    Blah, blah, blah!

    While you all are suggesting all kinds of answers, the correct answer is FIX THE FLOOR.

    This problem is almost a given in a mobile home of this age.

    Then install a 30/40 gal heater on #10 wire on that 30A breaker.

    I can do all of that, worst case, in a couple of hours and ImOld!

    Did I mention I had the same problem in an identical mobile home.:D
  14. kcodyjr

    kcodyjr New Member

    Messages:
    103
    Location:
    Chelmsford, MA
    Really, a 1971 Windsor? How did you bear the weight down to the ground?

    At that point in the trailer, it's supported beneath by metal triangular outriggers (zero thickness at outer edge) and within the floor by a single 2x4 laying on its side that I assume canitlevers weight back to the frame rails.

    Short of tearing the trailer open all the way to the centerline (toilet, vanity, bathroom floor, parts of the partition removed) to accommodate a piece of 3/4" hardwood plywood in a cantilever application, I just don't see what's going to hold it up.

    If it was located between the two frame rails, I'd agree without hesitation; fix the floor and be done with it. But, we're not talking about just fixing, we're talking about retrofitting it to handle weight it was never designed for.

    Re: 12 gauge not being enough. Why doesn't that surprise me... now I'm positive, there was no permit for that replumb. As though that wire just sticking out of the wall wasn't clue enough... yeah, no junction box or anything, just an torn hole in the wood paneling and a wire sticking out. I wish I knew the hack's name so I could report his sorry tail.
  15. kcodyjr

    kcodyjr New Member

    Messages:
    103
    Location:
    Chelmsford, MA
    Just dug it out of the closet to check the label. It says 3500 total connected watts, but also says the upper and lower elements each draw 3500 watts. Does that mean it only runs one at a time? Anyway, the manual says that a 20A circuit will suffice at that wattage, so I can be thankful for solutions to minor problems... now if only I can get a grip on the major ones.
  16. nukeman

    nukeman Nuclear Engineer

    Messages:
    711
    Location:
    VA
    Yes. Electric WHs will use only one element at a time. With a 30A breaker, you could run a 40, 50, etc. gallon heater (assuming you had the space and support). Most of the larger WHs have 4500W elements and some have 5400W elements.

    However, a 30A circuit normally protects a 10ga wire. Normally, you have a 20A breaker protecting a 12ga wire. I do know that mobile homes do not always follow the same codes as stick-built, but not sure offhand where the electric codes fall under that.

    With 3500W elements, you should be pulling about 15A, so the 12ga wire is okay from that point of view, but the 30A breaker still may not be correct.

    Maybe with some pictures of the structure under the WH, we might be able to come up with some way to better support it.
  17. guy48065

    guy48065 Member

    Messages:
    117
    Location:
    SE and north MI
    I'm in agreement with ImOld on this one. Water heaters haven't changed much in the 40 years since your MH was built--it was designed to handle the weight back then, so what does it need to meet the challenge today?
    Is the space the heater inhabits only supported by one cantilevered outrigger or will adding a new layer of 3/4 ply span 2 outriggers? Is the HWH located in its original spot or has it been moved? Having the wire come through a hole punched in the wall sure doesn't sound original-spec to me.
  18. ImOld

    ImOld New Member

    Messages:
    73
    Location:
    In the rumble seat
    Let's try again!

    The water heater is in the normal area, rear closet, for that type of mobile home.

    It is designed to be there.

    The fact that DIY's have screwed things up over the decades doesn't change that fact.

    I removed all the bad stuff, including an absolute maze of plumbing and wiring from a 3'X3' floor area.

    I then sister-ed floor joist material onto the good stuff.

    I then covered the area with 3/4" plywood and on top of that 1/2"of hardi cement board.

    At no time did I feel a need to add any support to the ground although you could with cement blocks and shims, just as the frame is being supported.

    This is the 12 year old, 30 gal water heater, that was removed and re-installed after the floor repair.

    Works as new.

    I love pictures.

    Attached Files:

  19. kcodyjr

    kcodyjr New Member

    Messages:
    103
    Location:
    Chelmsford, MA
    I don't believe the WH has been moved on the basis of a whole bunch of old crappy corroded copper tubing that converged on that spot in parallel with the newly poorly installed pex. I do believe the original heater was smaller though; there's supposed to be a linen closet above the space starting at 34" above the floor, which had been sloppily gutted to make room for a taller heater. Also, the idiot had taken a sawzall to the master bedroom closet wall to make the access opening taller.

    I should clarify, the underbody outriggers aren't cantilevered; they're welded to the I-beam, 9" in height there, and extend 32", about 2" short of the edge of the trailer. The spacing changes; there's one near the forward edge of the heater location, next one forward 3', next one back 4', but the measurements were imprecise. If I were to guess, either the spacing is in metric units, or the workmanship well and truly blows like nothing has ever blown in the history of workmanship, or blowing.

    Above that is a layer of some kind of board; thin, weak, and seemingly asphalt coated, or similar. Above that is a thin layer of factory fiberglass and a poly vapor barrier. Hey, wait a minute - that means the subfloor cavity is supposed to dry inward, which it won't in a bathroom. Duh, there's why a seeping tub turned into a big rot problem. Looks like I'm ripping out as much of that poly as I can see.

    Above that are the 2x4's on their side in the transverse direction. Those are the ones that cantilever weight. They're spaced 4' on center and don't quite line up with the outriggers below.

    Above that are irregularly spaced longitudinal 2x6 joists, notched where they ride over the transverse 2x4's, including a single thickness "rim joist" that doubles as a sill-in-midair.

    Next the factory put down 3/4" particle board subflooring, then 1/4" of finish flooring edge to edge, and then started building exterior, then interior walls. Yeah, stupid. Much of that has been ripped out and replaced already, and from what I've seen, without much regard to the fact that it's supposed to be holding the walls up.

    My first thought to handle the weight was to cantilever inward using some 3/4" hardwood ply, but it would mean tearing up the vanity, the partition separating the bathroom from the master bedroom, the toilet, and a few layers of flooring.

    My next thought is that I could expose more subfloor cavity about 2.5' sternward into the MBR closet, to reach the next transverse 2x4. The next one forward is under the tub and already exposed, but already subject to significant loading by the tub. Unfortunately, the next one forward of that is under my kitchen. There's an accessible void there, which stops 9" short of where that 2x4 would be. I'd think two extra 12' joists, spanning a total of four transverse 2x4's, just might do the job.

    I'll see what I can do about getting some pictures.
    Last edited: Nov 19, 2013
  20. kcodyjr

    kcodyjr New Member

    Messages:
    103
    Location:
    Chelmsford, MA
    That looks a good bit shorter than the one I have, and doesn't look any wider. Stanley McTape says mine is 45" high and 18" in diameter. If that wall plate is at the standard height for a lightswitch, mine would be blocking the view of it.

    Agreed that it's the location it's supposed to be, but it isn't the heater that's supposed to be there. It's definitely bigger than original, and neither the manual nor the tank says anything about being UL approved for mobile homes.
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