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DHW for four women

I live in a house full of women-one wife and three daughters. To make matters worse I have three full bathrooms-one with a stall shower and a large Jacuzzi soaking tub, so three of them could easily take long showers at the same time. Right now DHW is provided by the following:

Oil fired Buderus Logano G215
135Mbtu/hr Gross
117Mbtu/hr Net IBR
Grundfos circulator pump
46 gallon Bradford White storage tank
I don't know anything about the heat exchanger

Right now my oldest is 9 so we don't really have an issue right now, but I'm planning for the future. The only complaint I have now is that we really can't fill the soaking tub with hot water. Before the water gets deep enough (above the jets) the water goes ice cold and the tub ends up lukewarm. In any event, what would be the best way to expand the capacity of the system? I have plenty of room for another tank right next to the current tank.

Comments

  • SuperTech
    SuperTech Member Posts: 1,687
    A large indirect tank would be the best option. How well is the current setup working? I would make sure that the tank temperature is kept high, over 140 degrees at the minimum.  Definitely equip the tank with a quality thermostatic mixing valve to mix down the the hot water to about 120-125 degrees.  Keeping the tank hotter and mixing at the outlet of tank will increase the capacity of the tank.  
  • Larry Weingarten
    Larry Weingarten Member Posts: 2,281
    Hi, Everything @SuperTech says, and use low flow shower heads, like 1.5 gpm. ;)
    Yours, Larry
    kcoppfenkel
  • Robert_25
    Robert_25 Member Posts: 352
    Your existing setup is probably fine for everything but the big tub.  In addition to the items already mentioned, I would make sure the existing tank is piped properly.  A lot of indirects get installed with undersized piping and/or the wrong circulator.


  • heathead
    heathead Member Posts: 160
    I used to have a huge jacuzzi tub and standard 50 gal. 36k BTU Gas burner. Before I got a 80 gallon indirect It would be hard to fill the tub in the winter because of colder incoming water. I would crank water heater temperature up before using tub, and fill with the tub with hot side water only no cold water mixing at the tub, then it would fill with very hot water before it turned colder. It also helps to fill the tub slower with hot water only. It would work but you need the tempering value for safety. That tempering valve is the low hanging fruit in this. You should have that installed anyway and can try it before changing the indirect or adding to it. Measure the volume of the tub. Start by timing fill on a 5 gallon bucket down the the seconds. Then time amount of time to fill tub. Calculate tub volume and measure incoming water temp in winter. Then calculate everything. The numbers tell all. Good luck. I never have run out of hot water with the 80 gallon indirect now, and my boiler is only 60k BTU. The tub is the huge demand dump that needs to be calculated.
  • hot_rod
    hot_rod Member Posts: 15,012
    @heathead has it right, you need to know the capacity of that tub. I would say at least an 80 gallon, maybe a 120 gallon.
    You will find the family adjust to the amount of DHW you have available :)
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    kcopp
  • Zman
    Zman Member Posts: 6,965
    Do you have a separate flat plate exchanger or are using a tankless coil in the boiler? Does the boiler run at full output with no cycling during a DHW call?
    I think that much more storage is going to be the key. I would consider a 120 gallon indirect with an antiscald mixing valve which would allow you to run the tank hotter if more (effective) storage is needed.
    With those large tubs, the problem is usually the flow rate of the tub fill valve. I have a similar setup in my house, when I fill the tub with the valves partially closed, the water stays hot for the entire fill. You would be better off throttling the supply lines to the tubs with hidden valves than trying to convince the ladies that filling the tub more slowly will make it hotter :)
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • tim smith
    tim smith Member Posts: 2,397
    80 or 119 indirect depending on Jacuzzi size.
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 2,355
    edited December 2020
    Blessed art thou...

    We filled a 200-gallon tub with a Buderus oil fired boiler smaller than yours and a 40 gallon Buderus indirect tank. There was no problem getting there because we designed the boiler piping for maximum output. 1-1/4 supply and return from the tank to the boiler. The key is in the pipe sizing!

    You should have the capacity with the boiler you now own to generate about 3.5 GPM at a 70° temperature rise. This means that if you fill the tub at 3 GPM you should never go cold. That said... since you are experiencing a temperature drop over the filling time, there are one of two things happening. You are filling faster than the 3.5 GPM capacity of the system... or ... the transfer piping, heat exchanger, or pumping rate is not set up for maximum transfer rate. One or more of the links in that chain are too small.

    This could be the piping is too small to move the heat from the boiler to the exchanger, the exchanger is too small, or the piping from the exchanger to the tank is too small. wt some point in the future, when it is time to replace the tank, you might be well to purchase an indirect tank. Go for the 60 gallonish size and look at the transfer rates/capacity of the tank and use oversize piping. If the boiler tappings are 1-1/4" then for "Crips Sake", don't let the installer use 3/4" copper pipe to connect it to the boiler.

    I can't believe how many indirect and storage tanks I have seen with undersized piping. That one weak link in the chain can make all the difference.
    Edward Young
    Retired HVAC Contractor from So. Jersey Shore.
    Cleaned & services first oil heating system at age 16
  • Jamie Hall
    Jamie Hall Member Posts: 17,025
    There is another option. If you have space for another tank, you also have space for a direct fired, oil fired, hot water heater. Granted you would need a flue for it, but perhaps that could be done. Bock has at least one with a recovery rate of about 3 gallons per minute with a 50 gallon tank... you would have a hard time running it out of hot water.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 10,231
    Yeah, a bigger tank.

    But spending more time training the women not to all shower or bathe at the same time will be more productive.

    Good luck with that
    ethicalpaulEdTheHeaterManSuperTech
  • Jamie Hall
    Jamie Hall Member Posts: 17,025

    Yeah, a bigger tank.

    But spending more time training the women not to all shower or bathe at the same time will be more productive.

    Good luck with that

    Oh yeah. Right.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Big Ed_4
    Big Ed_4 Member Posts: 1,775
    If they had 40 gallons of hot water their shower would be 20 min , if they had 80 gallons of hot water their shower would be 40 min
    , if they had......
    I have enough experience to know , that I dont know it all
    Solid_Fuel_ManSweatyInToronto
  • Solid_Fuel_Man
    Solid_Fuel_Man Member Posts: 2,304
    I've got a 120 gallon indirect.....

    I keep the women happy. Happy wife happy life. It's a small price to pay! Showers are cheaper than cars!
    Serving Northern Maine HVAC & Controls. I burn wood, it smells good!
    EdTheHeaterMan
  • motoguy128
    motoguy128 Member Posts: 374
    Just add a 50 gallon electric as a storage tank in series after the indirect.  Doubled your storage and adds some supplemental heat on long draws.  

    Otherwise I’d just get them to at least take shower in series not simultaneously.  even a 46 gallon indirect can supply a single shower head almost continuously.  

    It’s the jacuzzi tub that’s the killer.  The electric tank will hell with that.  

    I have a single 40 gallon WM indirect snd we’ve taken 3 back to back showers while the dishwasher was running and didn’t run out.  It can supply a shower continuously and a dishwasher or clothes washer is easily handled by the storage.  We have a small whirlpool tub and no issues taking a shower after that. 

    The real challenge is simultaneously long draws.  But in reality you probably mommy have plumbing for about 5gpm peak flow.  
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 2,355

    Yeah, a bigger tank.

    But spending more time training the women not to all shower or bathe at the same time will be more productive.

    Good luck with that

    Training Women ... Yea ... Right... That always works out well! LOL
    Edward Young
    Retired HVAC Contractor from So. Jersey Shore.
    Cleaned & services first oil heating system at age 16
    Solid_Fuel_Man
  • mattmia2
    mattmia2 Member Posts: 3,941
    I think 5 people and 3 full baths would have sufficed..
  • Larry Weingarten
    Larry Weingarten Member Posts: 2,281
    Hi, Not sure if we're dealing more with physics or politics here, but I have found that plumbing teaches people how much hot water they have to use. People learn that when their hair is full of soap and the water is cooling down, it's not fun. Next shower time things get done differently somehow to avoid the dilemma. :# Maybe add a shut-off to that 1.5 gpm showerhead. o:)

    Yours, Larry
    Canucker
  • archibald tuttle
    archibald tuttle Member Posts: 818
    edited December 2020
    @Larry Weingarten maybe neither physics nor politics but pyschology

    @Jamie Hall what about a condensing propane on demand if flue is a problem.

    @Swamp_Yankee obviously that brings in the problem of piping in a [more?] sizeable propane tank. I'm assuming you don't have access to natural gas.

    what i have done with interior soaking tub is wrapped it in pex and made it a zone. i keep it filled and with a floating hot tub sterilizer thing (spa frog) and that takes care of that. no excess water use for the soaker and it's always ready and is a heating element for the bathroom when not in use. I don't know why they are not simply molded this way at this point.


  • mattmia2
    mattmia2 Member Posts: 3,941
    Probably because most people don't want a huge source of humidity and a science project in their bathroom.

    Running the tank hotter and using a tempering valve is the way to go(especially with a conventional boiler). The tank temp will vary with the indirect between when the boiler is heating up if it has been off a while, large demands that drop the temp to some lower equilibrium of the demand and what the boiler is supplying and overshoot from the hot boiler water sitting in the coil after the call ends. The thermostatic valve will give you hot water of a consistent temperature if it is applied correctly.
    SuperTech
  • hot_rod
    hot_rod Member Posts: 15,012
    Elevate the tank to 150 and use a top brand thermostatic valve. Two benefits, 30% more DHW and anti bacteria protection. Elevated temperature operation can shorten tank life however, more mineral precipitation
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    SweatyInToronto
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 10,231
    @EdTheHeaterMan

    When my son got to taking half hour showers I told him to cut it out........he didn't.

    So the next time he was in their too long I went down stairs and shut off the hot water, leaving the cold on of course.

    He got out pretty quick
    Le John
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 2,355
    edited December 2020
    I tried that @EBEBRATT-Ed . It did not go well with the wife or teen daughter.

    Here is an idea that might work. "For your chores, you will get an allowance of $ **.00 each week and 7 hot water tokens" (no price here because don't want to have @Erin Holohan Haskell scold me for price-fixing teen allowance rates)

    https://www.kingsupply.com/Token-Operated-Coin-Timer-p/coin-984.htm

    I remember thinking about getting a payphone installed in the daughter's room. (the was before cellphones and you paid extra for out of area calls)
    Edward Young
    Retired HVAC Contractor from So. Jersey Shore.
    Cleaned & services first oil heating system at age 16
  • mattmia2
    mattmia2 Member Posts: 3,941


    I remember thinking about getting a payphone installed in the daughter's room. (the was before cellphones and you paid extra for out of area calls)

    i remember that episode of the brady bunch
    EdTheHeaterManratioethicalpaul
  • archibald tuttle
    archibald tuttle Member Posts: 818
    mattmia2 said:

    Probably because most people don't want a huge source of humidity and a science project in their bathroom.

    you are the cautious type i think. me, i'm the guinea pig type. i've had the same water in there for two years. i'm thinking it might be time for a change. it's not growing anything. haven't died of legionaire yet. (maybe there is an advantage to the water having come from a deep well and i guess covering limits the constant open exchange with whatever is in the air - by all means let the public health folks chime in). I just cover it with a piece of XPS insulation when not using. very little humidity actually. I don't have a super sealed house but we're not getting anything like cloudy mirrors in the bathroom as if the shower were on all the time and i have never added any make up water and it's still full two years later. . . . Theoretically i installed a heat recovery ventilator that has bathroom outlets but i've never got around to getting it working because the house, much tighter than when i started, doesn't have symptoms of being overly tight so . . . priorities . . .

  • TAG
    TAG Member Posts: 489
    We had a big tub at a vacation place .... like most it was rarely used. Had it's own tank .... real waste. We took the tank out when it was getting up in age and got a dedicated electric on-demand for the tub. If you have the power it's an easy solution ... the cost to heat water for the times used is small and no standby loss.

    I also have an on demand for our outside shower at the beach -- they work great for dedicated single use ...hate them whole house
  • Solid_Fuel_Man
    Solid_Fuel_Man Member Posts: 2,304
    I've put in a few electric on-demand water heaters. 

    They work pretty well for a single use fixture which wont be used much. They will scale up and burn up the elements pretty quickly due to the high watt-density. 

    Most will end up with 2 double pole 50 or 60amp breakers. And will draw 80-100 Amps. So a 200 amp service is required. Pretty much the only real thing which will actually draw serious power in a residential setting.

    But for camps, and occasional use stuff they do work remarkably well. You can also use them to boost the temp of your existing hot water just for the tub. But only the PWM units will accept preheated water. The others are just a two or three stage flow switch and some contactors for the elements. 
    Serving Northern Maine HVAC & Controls. I burn wood, it smells good!
  • archibald tuttle
    archibald tuttle Member Posts: 818
    @Solid_Fuel_Man PWM ????

    you are absolutely right about these heaters being really useful in certain limited circumstances. I'm kind of ambivalent about how handy and relatively inexpensive they are. In this era of "demand management" for delivered utilities (and that kind of indicts NG on demand as well) I feel like they could overwhelm grid/pipe capacites.

    I guess the planners (people I generally have about zero faith in) are thinking that this can be handled stochastically by the low probability that everyone will turn them on at once.

  • Solid_Fuel_Man
    Solid_Fuel_Man Member Posts: 2,304
    PWM is pulse width modulation. Controlled by SCR's. Silicone controlled rectifier. Basically a solid state really fast switch. 

    Controls the heat output very accurately. 
    Serving Northern Maine HVAC & Controls. I burn wood, it smells good!
    archibald tuttle
  • Jamie Hall
    Jamie Hall Member Posts: 17,025
    @archibald tuttle -- you are so sadly right.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • SweatyInToronto
    SweatyInToronto Member Posts: 73
    hot_rod said:

    Elevate the tank to 150 and use a top brand thermostatic valve. Two benefits, 30% more DHW and anti bacteria protection. Elevated temperature operation can shorten tank life however, more mineral precipitation

    And replace the anode rod if haven't recently.

    What do you think about drain water heat recovery? More applicable to showers/cost savings but I guess warmer water into the boiler can increase recovery speed too.