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Hot Water Tanks and Sizes

kgk14 Member Posts: 24
My domestic hot water needs include capacity to fill a 30 gallon bathtub, take a shower and run a dishwasher at the same time.  I've received proposals that include a Super Stor 40, a Buderus SST150 40 gal, LAARS 40 gal stainless steel, a 40 gal TurboMax indirect, and a 50 gal State or AO Smith hybrid heat pump. 

I'm interested in a product that has good value (performance v cost) and will hold up over time.   Would also like to know if these units are sized right to meet my needs.  What do you recommend?


  • icesailor
    icesailor Member Posts: 7,265

    Your expectations of having enough hot water to do what you are asking is totally unreasonable. First of all, that 30 gallon bathtub doesn't use 30 gallons of straight hot water to fill it, and if the shower was using hot water, set at the code legal limit of 120 degrees, you would be seriously injured from scalding. The human body can't tolerate hot water sprayed on the body at 106 degrees for long. The dishwasher requires hot water settings of at least 130 degrees for the detergent to work properly. In spite of what is said about low temperature detergents. If you filled the bathtub with 120 degree water and got in it and stayed there, it will kill you. You will become hyperthermic, go into convulsions and die. if your body temperature goes over 106.

    If anyone that you received proposals tried to tell you what I just said, that's the one you should hire unless it is the one that told you that a 150 gallon Super Stor is your answer. Unless they also told you that for you to have that kind of available hit water, you need to re-pipe the whole house.

    Any others that didn't say the above, might not have an understanding of making domestic hot water.

    In my opinion.
  • Zman
    Zman Member Posts: 7,573

    You have fairly low hot water requirements.

    It sounds like you are trying to decide between an indirect and an electric.

    What is heating your hot water presently? How well does it work?

    What type of boiler do you have? What fuel does it run on?

    If you have an oversized oil boiler, the electric is usually a good option as it saves you money in the summer.

    If you have a high efficiency gas boiler, the indirect is usually a good call.

    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    The dishwasher requires hot water settings of at least 130 degrees for the detergent to work properly.

    I wondered about this, so I looked at the installation manual of my dishwasher. It did not really matter since the water piping is buried in my concrete slab along with the radiant heating tubing, and there is no separate water pipe for the dishwasher, so I could not supply water over 120F anyway. The water leaves my indirect at about 125F and the most I can get from the nearest tap is 120F. The dishwasher is some distance farther away, so it gets a little less.

    My dishwasher's owner's manual says:

    "Inlet Water Temperature: 120ᵒF (40ᵒC)"

    The installation manual says:

    "1. This dishwasher may be connected to either hot or cold water. If the water can not be maintained below 149ᵒF (65ᵒC), the dishwasher must be connected to cold water."

    Since it can run on cold water, I infer it has an electric heater in it. It must be on a dedicated circuit with a 15Amp circuit breaker. Well, the rest of it does not need 15 amp, so that must be for its internal water heater. Mine is hooked up to the hot water to minimize electrical cost.
  • kgk14
    kgk14 Member Posts: 24
    Tank Make and Size and Comps


    Yes, I am trying to decide between an indirect and an electric hybrid heat pump.  I have an old, inefficient cast iron tankless oil burner that provides scant hot water now, and I want to replace it, most likely with a high efficiency oil or propane boiler.  I've looked at various options and will decide soon. I am interested in anyone's recommendation or comments on the water tanks that have been proposed (see original post).   If there is a chart or other aid where one can do an apples to apples cost comparison based on usage of a heat pump hot water heater to an indirect off a high efficiency oil or propane boiler, please send or direct me to it. 
  • icesailor
    icesailor Member Posts: 7,265

    Yup, and if the dishes are really nasty, and you set it on a Sani setting, the heater heats the water to 150 degrees before it washes. And the dishes are cleaner.

    Dishwashers still need a 15 amp circuit.

    I use cold water detergent in my clothes washer. It works fine. Warm water works better,
  • icesailor
    icesailor Member Posts: 7,265
    Cost Analysis:

    If it's cost that is your concern, and you have a oil boiler with a tank less, buy a 30 to 50 gallon electric water heater connect it to the tank-less coil with a circulator and store the hot water in the tank. You do NOT connect the water heater electrical elements. They have no function in the tank except to plug the holes in the tank. Far cheaper than installing an indirect. If you are going to change from a oil to gas boiler, install an indirect of whatever you want. If you want cost for less or more for less, install a storage tank.
  • Rich_49
    Rich_49 Member Posts: 2,766
    Relax Ice

    a buderus sst150 is a 40 gallon tank that will provide 181 gph continuous .   I completely agree with your water temp opinion .  I just completed a house utilizing a Taco 5000 series mixer at the heater because we are storing at 160* because of demand in the home . The inspector would like me to turn the temp for whole house up to 130* and add a second device at the soaking tub to get that 120* or below . All the faucets are 8" 2  handle faucets with the exception of single lever tub / shower valves .  Refuse to perform this work and will see him at a construction board of appeals , will these guys ever follow the spirit of the code ?   
    You didn't get what you didn't pay for and it will never be what you thought it would .
    Langans Plumbing & Heating LLC
    Serving most of New Jersey, Eastern Pa .
    Consultation, Design & Installation anywhere
    Rich McGrath 732-581-3833
  • icesailor
    icesailor Member Posts: 7,265
    Another way:

    There's another way to do what you are doing, that will make the AHJ happy, or if not, he/she will be wrong. IMO.

    "Jetted Tubs/Soaking Tubs" use a huge amount of water. That 40 gallon Buderus SST150 40 gallon tank isn't big enough, no matter how hot you make it, and at 160 degrees, the tank won't last very long.

    Add a 50 gallon water heater tank (I always use electrics because they are cheap) and use the SST150 as a heat source like a side arm heater. Use that heater to just fill the tub. You don't have excessive demand, 24 hours a day, just occasionally. So, storage tanks work well. Like peak shaving in power generating.

    If there is any kind of a hand spray in the tub, it must be fed with a mixer. We usually set them under the tub with check valves so that they were always set to deliver legal water.

    It will be a lot more effective to add a storage tank to increase available hot water than to get into a urination contest with the AHJ's. You'll never win.

    In the late 1980's I did a 5 bath house with a 2 person jetted tub in the master bedroom. Spec'd by a designer. I installed a 50 gal. State Direct Vent gas water heater. I never heard a complaint. Two years later, I saw the owner and he told me that he needed a bigger water heater because he couldn't fill the tub without the water going cold. Everything else was fine. He wanted at least a 100 gallon heater. I told him I could add a storage tank and he would have 100 gallons of stored water. I installed a 50 gallon electric WITHOUT CONNECTING THE 240 VOLT and just used a Taco 006B. Never another complaint and still running after more than 25 years.
  • icesailor
    icesailor Member Posts: 7,265
    Rated Delivery

    "" "a buderus sst150 is a 40 gallon tank that will provide 181 gph continuous. " ""

    181 gallons of water weighs 1500+ pounds. Unless the boiler is rated at way above 150,000 BTU;s, I doubt that it will heat the water you want.