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Hot water production

KC_Jones
KC_Jones Member Posts: 4,625
So I read on here all the time about people being concerned about DHW production. Upsize boilers because they need enough, etc. I can't quite wrap my brain around it.

I run a standard 50 gallon 40k BTU tank water heater at 140. We regularly have all 5 family memebers take back to back showers, the wife (longest shower) goes first and I go last. Many times we don't even turn it off between children as one jumps in after the other. I will admit I can tell we are getting to the end during my shower, but it's still plenty hot. And to add insult to injury we do not have a water saving shower head. This thing will cause you physical pain if turned up to the max.

My question, why are some people so worried about this? Is this really a problem? Are people running hot water continuous for several hours? I only have my experience to go by, just can't get my brain around what I read on here. Another point, I've never seen a concerned post with more than 5 people, so I'm trying to do an apples to apples comparison to my situation.

This has me very curious.
2014 Weil Mclain EG-40
EcoSteam ES-20 Advanced Boiler Control
Boiler pictures updated 2/21/15
https://www.facebook.com/media/set/?set=a.10202744301871904.1073741828.1330391881&type=1&l=c34ad6ee78

Comments

  • hot_rod
    hot_rod Member Posts: 14,552
    I've found families are more sensitive to DHW, or lack mod, then heat:)

    And the amount DHW families want, or think they need varies widely.

    I also found that high use families can often never get enough, give them 80 and they want 100 gallons, different mindset.

    We are fine with a small tank, 40 gallon talk or combi able to supply 2 gpm.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    hvac
  • Zman
    Zman Member Posts: 6,454
    Most contractors do not understand the relationship between storage and production and do not understand the universal hydronic formula. Homeowners also know very little about the subject and only know to complain if their house is not warm or they run out of hot water.

    Most contractors install grossly oversize equipment because they don't know how to properly size it and have learned that when in doubt, go bigger.

    The most aggravating conversation I have is trying to convince contractors and supply house designers that you don't need to match the boiler to the indirect. Just because the 80 gallon model will produce "x" GPM at "y" Btu input does not mean cannot produce adequate hot water with a smaller boiler. You just need to understand 5th grade math and figure it out.

    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • Docfletcher
    Docfletcher Member Posts: 476
    We have the HTP SSC-35 contender indirect , gobs of hot water, even though I reduced from 1" to 3/4" at the boiler. It was fine even when there were 4 of us here. Our boiler is over sized by 40000 btu but even if it were not I'm sure the contender would be just fine.
  • STEVEusaPA
    STEVEusaPA Member Posts: 4,823
    edited November 2018
    When I was a kid, we were told to shower faster. If it ran out, oh well. I remember we originally had an electric water heater with the extra electric meter that shut off power to the water heater (I think over night.
    That was 2 parents, grandmom, 5 kids (2 of them girls), one bathroom.
    steve
  • hot_rod
    hot_rod Member Posts: 14,552
    Folks that need large amounts of DHW, might also drive 600 HP passenger cars :)
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Leonard
    Leonard Member Posts: 903
    edited November 2018
    At least 4 main variables, input water temp, shower temp, flow rate, stored water temp.

    Input (ground) water temp varys north to south. In winter in Miami can wash your hands in cold water (~70 deg) , not so here in NH in February (42degs). What state are you in?

    Also depends on what you consider a hot shower. What wife considers hot I consider cold. I like it steamy 100+ degs to make back pain go away. I filled a 5 gal bucket for 1 minute during a shower, measured gallons and it's temperature.


    I don't have low flow shower head either. Have tankless DHW coil in furnace water jacket. I'm in NH, takes 88k BTU/hr to water to heat 3 GPM from 42 degs to 101 degs. If down south or take cooler shower that 60 deg temp rise might be cut in 1/2 and a ~ 44k BTU/hr heat input would be OK for 24/7/365 continuous run

    I taped a thermocouple on city water pipe where it came into the house, measured cold water temp while wife took a shower.

    Our city water is supplied by a HUGE lake, ~ 1--3 miles across. I suspect our water might be bit warmer if supplied by a well, don't know.

    OF course can run hot water storage tank HOT and temper hot water line with mixing valve at tank for extra shower time,

  • KC_Jones
    KC_Jones Member Posts: 4,625
    I'm in PA, city water, I go last and take a shower that Almost melts my skin. Yes I run it high and temper down, which makes a difference.
    2014 Weil Mclain EG-40
    EcoSteam ES-20 Advanced Boiler Control
    Boiler pictures updated 2/21/15
    https://www.facebook.com/media/set/?set=a.10202744301871904.1073741828.1330391881&type=1&l=c34ad6ee78
  • Gordy
    Gordy Member Posts: 9,530
    This seems to always come up when sizing a mod/con when heating loads are low.

    As you said a conventional DWH has less output than the smallest mod/cons available.

    If you use an imdirect of proper size and an extended temp setting I don’t see any issue unless there are large tubs, or car wash shower heads. Up size the indirect to compensate.

    Combos are limited with multiple fixtures.
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 8,540
    40 gallon gas hot water tank or an indirect with 40,000input is plenty for most houses. Unless they have a whirlpool tub or something.

    But then again I watch a lot of the home remodeling shows and there are plenty of houses with 3,4 or 5 bathrooms. There is usually not more people in these homes just more bathrooms. Maybe they leave the hot water running in all the bathrooms all the time
    Gordy
  • Leonard
    Leonard Member Posts: 903
    edited November 2018
    From my BTU/hr DHW measurements, tankless DHW requirements can drive furnace sizing.

    I have over sized furnace, it's sized to also heat 2nd floor that was never finished/heated. It used to have ~ 1.35 GPH nossel. Slowly tried smaller ones till got to ~ .95, That was too small, had to drop room thermostat setting while showering to keep shower HOT in February. Bumped nossel up to ~ 1.1, no more cool showers while heating house.
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