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Sizing up a gas hot water heater ---

sanblas
sanblas Member Posts: 19
I am looking for a gas hot water heater that works separate from the heating boiler.
House is a 6 family, has 6 baths and 6 kitchens. 2 roommates in each apartment. How do i calculate what tank i need to buy?
From this forum i see that lots of people use bradford white or ao smith. Any recommendations to a specific model ? Preferably a high efficiency long lasting product.

Any help is appreciated!!

Comments

  • sanblas
    sanblas Member Posts: 19
    Thank you. I already like what i see. Glad i asked the question. Any other options ?
  • RobG
    RobG Member Posts: 1,850
    Do you have a heating boiler already? If you do an indirect or reverse indirect might be a better fit. Why have two appliances when one will do the job and not require any additional venting?
    jonny88
  • Rich_49
    Rich_49 Member Posts: 2,766
    The 76k unit light duty probably won't do that kinda demand . Maybe with the 80 gallon tank . If they have the hot water available they will use it more . Human nature Hat . He would probably be better off with the PH100-80 , don't think the 130 would be necessary though .
    You didn't get what you didn't pay for and it will never be what you thought it would .
    Langans Plumbing & Heating LLC
    732-751-1560
    Serving most of New Jersey, Eastern Pa .
    Consultation, Design & Installation anywhere
    Rich McGrath 732-581-3833
  • RobG
    RobG Member Posts: 1,850

    RobG said:

    If you do an indirect or reverse indirect might be a better fit. Why have two appliances when one will do the job and not require any additional venting?

    Venting issues aside, he'd need to leave the boiler at 190/170 24/7/365 to be sure of meeting the hot water needs, and he still needs an 80 gallon indirect.

    All the losses from the boiler that must remain at high temperature............forever. Kind of reminds me of the old tankless coils where the boiler had to be kept at 180°F. year round. How'd that efficiency work out?

    It's not like a residential unit that can live most of its life at a lower temperature and rise on a call from the indirect.
    That is a completely incorrect statement. The boiler only has to fire when the tank aquastat calls for heat.
    Charlie from wmassjonny88icesailor
  • sanblas
    sanblas Member Posts: 19
    Thanks guys. I rather be on the safe side and go with the larger one instead of getting complains!
    This forum is great!
  • RobG
    RobG Member Posts: 1,850
    I'll tell you how much, the same or less than a tank type water heater. Why do you think they make indirect water heaters?
  • wogpa67
    wogpa67 Member Posts: 238
    If there's no mixing valve a minimum of 12 times.

    Do you have laundry facilities and dishwashers on site?
  • RobG
    RobG Member Posts: 1,850
    You are completely mistaken but I'm going home now and this can be taken up tomorrow.
  • sanblas
    sanblas Member Posts: 19
    I realized the pheonix requires direct venting to outside. This is not possible in my case. Any other models that can vent/share a chimney with a gas boiler?
  • Rich_49
    Rich_49 Member Posts: 2,766
    HTP even has better stuff than the competition in lower efficiencies Hat .

    http://htproducts.com/htp-heavy-duty-gas-water-heater.html

    You are right though , many confuse high efficiency with high output .
    You didn't get what you didn't pay for and it will never be what you thought it would .
    Langans Plumbing & Heating LLC
    732-751-1560
    Serving most of New Jersey, Eastern Pa .
    Consultation, Design & Installation anywhere
    Rich McGrath 732-581-3833
  • Rich_49
    Rich_49 Member Posts: 2,766
    You'll get no argument from me about that .
    You didn't get what you didn't pay for and it will never be what you thought it would .
    Langans Plumbing & Heating LLC
    732-751-1560
    Serving most of New Jersey, Eastern Pa .
    Consultation, Design & Installation anywhere
    Rich McGrath 732-581-3833
  • Matt_67
    Matt_67 Member Posts: 284
    Not arguing - but shouldn't we know his cold water temperature to make a recommendation? Where I live our water is 34-35 degrees in the winter and it makes a huge difference in performance.
  • Rich_49
    Rich_49 Member Posts: 2,766
    edited April 2015
    Matt , a condensing technology water heater will always be more efficient . Especially with a colder entering water temp because more energy can be transferred the larger the temp difference .
    So, in short , NO . We do not need to know his incoming water temp , only that it is incoming and needs to be heated .

    The units we are discussing deal with a 100* temp rise right in the specs .
    a condensing type heat exchanger will always perform to a higher efficiency with colder entering water temps . Out may vary but not performance . Don't confuse the two .
    You didn't get what you didn't pay for and it will never be what you thought it would .
    Langans Plumbing & Heating LLC
    732-751-1560
    Serving most of New Jersey, Eastern Pa .
    Consultation, Design & Installation anywhere
    Rich McGrath 732-581-3833
  • sanblas
    sanblas Member Posts: 19
    Thanks for all the technical info! I will vent to the side. Lots of more work but worth it
  • jonny88
    jonny88 Member Posts: 1,139
    @Hatterasguy I see you converted to the HTP. Good idea to listen to Rich eh....... "joking ok."
    RobG
  • RobG
    RobG Member Posts: 1,850
    jonny88 said:

    @Hatterasguy I see you converted to the HTP. Good idea to listen to Rich eh....... "joking ok."

    I think Rich gets kickbacks from HTP. :p
    Rich_49
  • Rich_49
    Rich_49 Member Posts: 2,766
    edited May 2015
    Although I find that amusing could we please refrain from even mentioning that impossibility ? That sounds alot like some veil of impropreity and ethical situation that could not be farther from the truth .
    Let it be known that I have no ties with any manufacturer . I choose my equipment possibly different than others based on what I know , how it will perform a certain function and to make my life and the end users easier . I am not alone in the thinking that tight channeled wall hung mod cons and what must sometimes be added to the system to insure they operate the way they should will serve them up a shrinking market as they drive costs up also .

    Once again , RobG , I do get the humor there but please do not cast me in that kind of light of perception in the future .
    You didn't get what you didn't pay for and it will never be what you thought it would .
    Langans Plumbing & Heating LLC
    732-751-1560
    Serving most of New Jersey, Eastern Pa .
    Consultation, Design & Installation anywhere
    Rich McGrath 732-581-3833
  • icesailor
    icesailor Member Posts: 7,265
    Rich said:

    Matt , a condensing technology water heater will always be more efficient . Especially with a colder entering water temp because more energy can be transferred the larger the temp difference .
    So, in short , NO . We do not need to know his incoming water temp , only that it is incoming and needs to be heated .

    The units we are discussing deal with a 100* temp rise right in the specs .
    a condensing type heat exchanger will always perform to a higher efficiency with colder entering water temps . Out may vary but not performance . Don't confuse the two .

    That's not quite true.

    To a heater, doing DHW plumbing, it isn't true. To a Plumber that understands DHW/Potable water heating, it definitely isn't true.

    If you need a bigger water heater, you can raise the temperature and store more hotter water. Which theoretically increases the size of the tank.

    When you lower the incoming water temperature, you increase the demand for energy. It takes more energy to heat a 50 gallon water heater with 35 degree incoming water than the same heater that has 55 degree incoming water to the same temperature in the same amount of time. BTU's Per Hour. With a heating system dealing with a 20 degree Delta T to whatever temperature you may choose, you only raise the temperature 20 degrees. In a Potable water heater, if the stored or discharge temperature is 155 degrees, and the incoming cold water is 35 degrees, the Delta T is 120 degrees. The 155 degree water isn't recovered and recycled. It goes down the drain.

    When it is cold outside, you can leave a window open and still have a warm house. Leave a potable hot water faucet running, and you will quickly run out of hot water. Its a really bad misconception. Unless you have done a lot of service work on potable DHW systems in hotels, motels, restaurants, hospitals and nursing homes, you have no idea how fast you can run out of hot water, and what it takes to recover it. Most people think of recovery in BTU's Per Hour. What will it take if you change a 80 gallon commercial gas water heater to a high performance 60 gallon water heater. That extra 20 gallons you gave up may need twice the input to recover that lost 20 gallons with quick needs. Especially in restaurants or commercial kitchens. You never know what or when a dishwasher dumps the contents of a pot sink and refills it with hot water in the middle of dinner. Same with the wash water in a commercial dishwasher. When the wash tank gets nasty, you have to dump it and re-fill it. And there's no hot water left because the water heater isn't big enough. Boilers are rated through that universal hydronic formula of 20 degree Delta T at X GPM. Water heaters aren't.

    In my experience.

  • Rich_49
    Rich_49 Member Posts: 2,766
    edited May 2015
    Could it be possible that you Icesailor don't quite get the magic " up to ?% efficient numbers . Could you also be not quite up to speed that a wider Delta T allows more heat transfer ?
    I remind you thast these are not what you installed Ice . IME for you was quite some time ago , no offense meant .
    When you theoretically increase the storage capacity of the tank you also lessen the amount of cold entering fluid and in a mod con water heater you can also WRING more BTUs out of the HX and into the fluid . Lower flue gas temps and all .
    So while your output may be slightly less your appliance will be operating at a higher efficiency . This is a system and not just one part , plumbers and heaters know that .
    Ice , those boilers which are in essence the same as water heaters except for the Delta T thing are also at their max efficiency with lower EWTs . Correct?
    You didn't get what you didn't pay for and it will never be what you thought it would .
    Langans Plumbing & Heating LLC
    732-751-1560
    Serving most of New Jersey, Eastern Pa .
    Consultation, Design & Installation anywhere
    Rich McGrath 732-581-3833
  • icesailor
    icesailor Member Posts: 7,265
    @Rich:

    You're talking "Space Heating". I'm talking "Water Heating". Domestic water heating.

    You're talking Mod-Con space heating boilers. I'm talking Potable Hot Water Heating.

    For uncalculated round numbers, if you have a building that looses 100,000 BTU's with 180 degree water on design day of zero OAT, and you are maintaining 70 degrees IAT, and you shut off the boiler to work on the system, and the system drops to 70 degrees or less, and after 8 hours, you turn the system back on, the building will not heat up to 70 degree inside until the OAT goes up.

    The same scenario when the temperature is 35 degrees outside, and the boiler is twice the size needed. It will heat up. Or why some don't do heating system repairs on a cold day. You can have all the cold exhaust efficiencies you want. They only apply to heating. And I still haven't seen anyone call for that on steam boilers.

    With potable DHW, Its always cold outside. Because the incoming cold water is cold. It has to be heated up to the temperature that is needed. Every day of the year. Regardless of the OAT. DHW works in an environment like the OAT is constantly going up and down. The inlet temperature always remains about the same. Its the outlet and storage that goes up and down.

    A commercial application like a hotel with a restaurant, laundry and rooms has two Bock 73E oil fired water heaters, each fired at 1.75 GPH (Gross 490,000 BTU's) and each recover 220 gallons per hour at 100 degree rise. So you have 440 gallons recovery with 140 degrees stored. That comes to over 600 gallons for a first hour draw. If someone in the kitchen decides to fill a triple bay pot sink with hot water, the dishwasher is washing dishes, and people want to take showers or baths in the rooms. they will run out quickly. Because the whole mess is being cooled with 50 degree water. You space out your usage. That never happens in a heating system.

    As far as flow rates? The only way to accurately know what is going on (my experience) is to know the flow head through the circulator, look on the flow chart for that particular circulator, Once they know the pressure, they convert it to head pressure, and then the chart gives you the GPM. Measuring the Supply & Return temperature gives you the BTU output. If you don't know the actual/accurate flow in GPM, you're just guesstimating.

    Put your hand onto the boiler supply of a Indirect and the return. You can have a 30 GPM, 50' head pump, pumping through the coil with 180 degrees coming and going with a lukewarm tank, the coil is probably dirty. Slow the flow down to 1 GPM. If the water returning gets hot, its a dirty coil. It means Jack Schitt what the rated output the manufacturer says. That's for a new and perfectly clean indirect coil.

    Commercial buildings with heating systems designed by ME's and all the flow characteristics of the design, have circuit setters, where some certified circuit setter comes along with his/her briefcase full of magic wheels for all the different circulators, and take an oversized circulator, and set the setters so that every circuit has the correct pressure/flow through it to have balanced flow throughout the system.

    HINT!!! Want to really "F" something up? Reset all the circuit setters to wide open. Watch what happens when someone that doesn't understand what happened, try to figure it out.

    DON'T TOUCH THOSE CIRCUIT SETTERS!!! THEY ARE LOCKED IN PLACE WITH THAT TAG FOR A REASON!!.

    There are no circuit setters on a water heater.



  • Rich_49
    Rich_49 Member Posts: 2,766
    Here's a hint for ya Ice ! We are discussing modulating condensing water heaters with a high storage temp anf mixing valves . The sensors in these are placed in a way that when I design one for a situation or the worst case I can virtually guarantee there is nothing any idiot able to turn a faucet on or off can do to run it out of hot water .
    here is another hint along with a question . A modulating condensing water heater is no different than a modulating condensing boiler save for one thing , the water heater as you stated always has cold water entering . This insures that the burner will always deliver more energy to the fluid . Colder EWT = higher efficiency % .

    please see the following 2 links to understand .

    http://www.htproducts.com/pioneer.html

    http://www.htproducts.com/phoenixwaterheater.html

    Can you tell the difference ? I can tell you what the difference is , 1 is white , the other black , one's controls and sensors are set up for 180* and the other 160* .
    Yes , Ice , they are one in the same . Pay attention a bit more often . This is not your grandfathers boiler nor is it his water heater . Welcome to the 21st century .

    Maybe the ME in your example should have paid closer attention in class and he might've learned how to properly balance and design a system that did not require so may devices and people to make it work right .
    Steam boilers , circulators and circuit setters , Oh my . how did they ever enter a discussion about DHW ?
    You didn't get what you didn't pay for and it will never be what you thought it would .
    Langans Plumbing & Heating LLC
    732-751-1560
    Serving most of New Jersey, Eastern Pa .
    Consultation, Design & Installation anywhere
    Rich McGrath 732-581-3833