How BIG do I buy 30 or 40 gallon?

Discussion in 'Water Heater Forum, Tanks' started by sherri, Apr 27, 2010.

  1. sherri

    sherri New Member

    Messages:
    1
    Location:
    Florida
    I am single in Florida and my water heater went out. It is what the plumber says is a "LOW BOY", which to me means that it is shorter than the regular ones. I read the label which states that it is 40 gallon. But my question is this - I'm not here that often and I travel. Sometimes friends from up north come down to visit but that is sporadic, and maybe happens twice a year. Can I get by with the 30 gallon low boy or should I just put in what came with the house originally?

    I hate paying extra electric for a larger water heater, when I'm not here. If I cannot notice a difference, I'd just get the 30 gallon. Am I making a mistake? What say ye, professionals?


    Thanks for any help figuring this out!

    Sherri
  2. johnjh2o1

    johnjh2o1 Plumbing Contractor for 49 years

    Messages:
    1,143
    Location:
    South*East
    I would say a 30 should be fine. If the heater is under the AC unit as most low boys are here in Florida. There is a good chance that a new 40 won't fit there any way. The new 40 lows are bigger in diameter then the old.

    John
  3. Dana

    Dana In the trades

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    The difference in standby loss between a 30 vs. 40 gallon lowboy is quite small- look at their EF ratings. EF 0.90 units will have the same standby loss, independent of tank volume. Unless you like to take super-long showers, or have multiple guests, taking showers one after another a 30 gallon unit will be just fine in warm-water FL. (It draws substantially less hot water from the tank to take a shower when you're mixing it with 65-75F water from the street as opposed to areas that have 40F water.)

    But for when you're leaving town there's nothing quite like turning off the breaker to the HW heater before you leave for taking the standby power down to zero. The only downside to that approach is you'll have to wait for the hot water to heat up before showering after you come home from a trip, but again, heating water from 70F room temp to 115F showering temp just doesn't take all that long, and with the same heating elements, a 30 gallon unit takes only 3/4 the time to heat up as a 40 gallon unit. This approach is commonly taken on vacation & weekend-getaway places. If you think you might want to try it, when comparing units, look at both EF numbers and the wattage. (Higher is better for both.)
  4. hj

    hj Moderator & Master Plumber Staff Member

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    Location:
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    In many cases, a 30 gallon heater is going to cost the same, OR MORE, than a 40, due to the economies of scale in producing them. There is little difference in operating costs between them. You heat the water you actually use, and reheat what is in the tank when it is dormant. The only thing that increases the efficiency of an electric heater is more insulation. There is a limit to how high wattage elements you can use, and they are exactly the same regardless of the heater's size.
  5. Redwood

    Redwood Master Plumber

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    7,450
    Location:
    Connecticut
    Yep! HJ's right! Here the 30 gallon costs $25 more than a 40 at the supply house...
  6. Dana

    Dana In the trades

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    Is that true for low-boys as well? I had thought there were a lot of 30 gallon low-boys being installed in mobile homes & 1-br apartments these days, and that they might be slighly cheaper than 40 & 50 gal low-boys. A quck internet search says the difference is "in the noise"- priced about the same.

    Within a manufacturer's model/line there seems to be a 0.01 EF advantage with a 30 gallon version vs. a 40 gallon version (eg. EF 0.93 for the 30 gal vs. EF0.92 for the 40 gallon version.) That may not seem like much, but it's about a ~10% reduction in standby loss going with the smaller unit- primarily a function of less surface area at the same R-value. Insulating the near-tank pluming with closed cell foam pipe insulation would probably make a bigger difference though.
  7. cacher_chick

    cacher_chick Test, Don't Guess!

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    Location:
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    If there will ever be a need to wash a load of laundry and take a shower consecutively, you will have greater satisfaction if you don't run out of hot water.
  8. Dana

    Dana In the trades

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    Running out of HW with only a 30 gallon tank is more likely in the land of cheese than in the warm swamps of Florida where incoming water temps in winter are 30F lower than typical FL temps, but neither is in great danger with consecutive washer + shower draws. A 10 minute 2.5 gpm shower @ 105F with 35F incoming water uses ~20 gallons of 120F water, but with 65F incoming water it's only ~18gallons. If the storage temps are 125F the HW volumes are lower 120F is something of a lower-limit. If your shower head is only running 2gpm (about where many 2.5gpm-rated showerheads actually run except in high water-pressure areas), it's more like 16 gallons in cold-water country, 14 gallons in FL.

    A clunky full-size old-skool top loading washer will use ~40 gallons of water, but not all cycles need to be hot water- a warm-wash/cold-rinse will draw ~8-10 gallons from the HW tank, but hot-wash/cold rinse will draw 16-20 gallons from the tank. A water-sipping mid-size front-loader will use roughly 1/3 the hot water of a top loader as long as the rinse cycle is cold: 3-4 gallons for a warm-wash, 6-7 gallons for hot-wash. It's not as favorable if the rinse cycle is warm or hot (since more water is use in the rinse than the wash cycles on front-loaders) making it more like 2/3 of the hot-water draw of a top loader on similar warm/hot settings.

    With either a hot wash/warm-rinse front loader or warm-wash/cold rinse top-loader followed by (or concurrent with!) a 10 minute shower scenario the 30 gallon tank keeps up in FL but will fall short in WI. And a hot-wash/warm-rinse with a full sized top loader would be an issue for taking long showers even with a 40 gallon tank. (With the slow recovery rates of tanks, it's possible to do-in almost any sized tank if you work at it, as teenagers all over America prove daily! :) ) First hour ratings on 30 gallon tanks are tyically in the ~45gallon range, but 40 gallon tanks are only in the mid-50s, only 20-25% more, not the 30-35% more that the storage size might imply.

    And of course, taking the shower first, letting the washer use the possibly-tepid water is still an option if it falls short. A 10-25F reduction in temp at the middle or end of the cycle is a disaster in a shower, but not so much for a washer- the hottest water would be used for the wash, even if the warm-rinse ran tepid. And again, in warm-water FL the transition to cooler-water at the end much less jarring than in frigid WI.
  9. cacher_chick

    cacher_chick Test, Don't Guess!

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    Location:
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    Very informative post Dana, thanks for that!
    I guess part of the problem is my showers tend to be at least 20 minutes. ;o)
  10. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,825
    Location:
    Cave Creek, Arizona
    The cost of the heater is not in how many are being installed, but rather how many are being made. And there are MANY, MANY more 40 gallon heaters of ALL heights produced than 30 gallon ones. A 30 gallon ELECTRIC heater has such a limited application, (and a 40 or 50 usually fits in the same location), that there is little incentive to go with the smaller heater.
  11. Dana

    Dana In the trades

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    I agree there's little incentive for going smaller, and yet, internet-pricing of 30 gallon electric lowboys is within $40 of 40 gallon versions, and usually cheaper than the 40 within a manufacturers model line. The price delta seems inconsequential relative to the whole cost of installation.

    The number made vs. installed numbers are by definition identical over time. The price is relative to demand vs. supply, which is an installation vs. manufacturing rate, with a small amount of manufacturer's material-cost delta. Whether they're installing 5x as many 40 gallon as 30 gallon lowboys or not, as-measured by the internet price, the rate of manufacture of either is commensurate with the market demand.
  12. MACPLUMB 777

    MACPLUMB 777 TROJAN WORLDWIDE SALES RP

    Messages:
    679
    Location:
    Houston, Texas, United States
    ALSO BE AWARE IF YOU ARE GONE FOR A PERIOD OF TIME THEN BE AWARE OF THIS



    CAN A DISHWASHER EXPLODE
    YES

    It is not the dishwasher however; it is hydrogen sulfide gas created in the hot water heater of a vacant house that caused it. Hydrogen sulfide gas is flammable and in confined spaces can be explosive. If a dishwasher explosion occurs it can cause damage and possibly personal injury.

    PROBLEM

    The problem is two fold. The first is the formation of gas in the hot water heater. The gas forms because anaerobic bacteria in the water react with the metal anode in the hot water heater. This anode is made from magnesium and is there to prevent corrosion inside the water heater. If the hot water is not used for some time, usually considered to be over two weeks; magnesium in contact with the bacteria causes the gas to form. Since the water is not moving the gas has no where to go so it remains in solution in the hot water heater. When a valve is opened the hot water flows and the hydrogen sulfide gas comes out of solution and flows with it.

    The second problem is the introduction of a spark into the gaseous atmosphere. The spark can come from an exposed switch, motor or timer in the dishwasher. As the dishwasher fills, the water level rises in the bottom. A water level switch inside the dishwasher will activate to shut off the flow of water when it reaches the proper level. If this switch or any other open switch or motor sparks inside the dishwasher, it can ignite the gas. Hydrogen sulfide gas can be easily ignited.

    SOLUTION

    The best solution is that if your residence has been vacant over two weeks do not run the dishwasher until you have fully opened all faucets and allow them to run for a minimum of 10 minutes. Do not have any source of ignition such as a cigarette, candle, stove, oven or other source while you are doing this. It is also suggested that you completely drain the hot water heater at least twice.

    The reason for this is to release hydrogen sulfide gas which may be in the water lines. If you run the dishwasher and this gas is present, the gas in the dishwasher could explode.

    If you smell rotten eggs while the faucets are open that is hydrogen sulfide gas.

    This is especially important in foreclosed properties where the residence may have been vacant for months.
    Last edited: May 1, 2010
  13. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,825
    Location:
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    THere are NO components in a dishwasher that produce an "open spark" ANYWHERE, and especially NOT in the chamber itself. Any stories of Dishwashers exploding probably belong with other urban legends like alligators in the sewer system. The number of heaters produced versus those installed will be equal in the "big picture" but in any given locality, it may seem that one size is very "popular", but that might not hold true for the entire population. YOU may install a "lot" of 30 gallon water heaters, but I have installed a SINGLE one in the past 20 years. I could show you exactly where that one is, but the occupants sold the house a decade or more ago, and both have passed on since then.
    Last edited: May 1, 2010
  14. Scuba_Dave

    Scuba_Dave Extreme DIY Homeowner

    Messages:
    885
    Location:
    South of Boston, MA
    I can run a 40g out of water with a shower...in the summer
  15. Dana

    Dana In the trades

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    I know folks who could drain a 100 gallon electric tank in FLORIDA in summer with a shower, eh? ;-)

    Your incoming water temps in MA rarely break out of the low 50s, in FL they're rarely below the high-60s- it's enough to make a difference. But unless you have a tankless hot water heater, it's ALWAYS possible to run out. (The #1 selling point of tankless heaters.)
  16. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,825
    Location:
    Cave Creek, Arizona
    One thing which has not been addressed is what she means by "Low boy". It could mean a "short" heater as opposed to the tall narrower ones, but it could also be a "32 inch high countertop" heater meant for installation in a cabinet, which changes the pricing and installation structure.
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