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Recomendation for 2 DHW tanks; Series or parallen equal distance?

Empire_2Empire_2 Member Posts: 2,343
Currently have a job with 2 tanks, 1 40 gal, 1 50 gal. It has been piped in series, but I am not sure if this is the best Idea? Any help greatly appreciated. The reason the tanks are mismatched is that they added a large spa type tube and needed more hot water so someone piped the 50 gal. in series.

Comments

  • icesailoricesailor Member Posts: 7,265
    Piping in series is a fine thing. Especially if they are electric water heaters. The first heater comes on as soon as the cold water hits the thermostat, and the second tank won't come on until the first tank is exhausted of hot water.

    When they are carefully piped in parallel, both elements will come on at about the same time, and you have double the recovery. If one tank is shorter/smaller than the other, they tend to balance out and get cold at the same time. The must be as close to perfectly balanced as you can make them with the connections exactly between the inlets and the outlets of the two tanks. If not, they won't be balanced. And the tank with the least resistance will run out first. There are all kinds of ways to do it. Series piping isn't one that is recommended.
  • AbracadabraAbracadabra Member Posts: 1,948
    Use reverse return. I wouldn't use parallel on different sized tanks.
    Henry
  • clammyclammy Member Posts: 2,501
    Usually all the multi tank jobs including multi storage tank jobs i have done i have always piped them in parrell and didn t have any issue with temp differentals between tanks.I usually always tryed to keep it all even meaning same amount of ells,isolation valves and pipe lgth before tying into my main tees .I usually split my inlet cold n hot mains using tee and piped it bull headed i know this is a no no for hydronics and pumps but this way the drop is even on the split and feeding and exiting the tanks .Im big on using unions so i always set up these types of jobs with unions i feel that may be in the future if so havs to replace the tank it can be done easly with having to repipe and possible screw things up (knuckle head it) Hope this helps some where amoung all books and refrence crap i have there s some clear manafacture info .I believe my example may be from a old rheem hand book peace and good luck clammy
    R.A. Calmbacher L.L.C. HVAC
    NJ Master HVAC Lic.
    Mahwah, NJ
    Specializing in steam and hydronic heating
    icesailor
  • AbracadabraAbracadabra Member Posts: 1,948
    edited March 2015
    @clammy I've always used parallel on same sized multi-tank DHW jobs, but parallel on different sized tanks?
  • Empire_2Empire_2 Member Posts: 2,343
    Thanks gentlemen...

    Mike T.
  • clammyclammy Member Posts: 2,501
    Good point on the differnt size thanks .I had to do a re pipe on a job years ago that had issues and they where pipe in series and differnt sized tanks .I re piped parrell and it was a vast improvement but still was not hot enough for what the custermer wanted .As for a reverse retrun on portable i ve never done it but use it for multi boilers,hydronic sysytems and feeding multi indirects i always use the proper piping when necessary .i was going off what i ve done and i m pretty sure i went to the book i ain t that smart to think this stuff up and i don t like to make my custermers pay for my guess work no they always want the same as i postive results ? Usually when faced with doubts i go to manafactures techincal literture and in this computer age is pretty easy some times easer then finding it on my book shelf .peace and good luck clammy
    R.A. Calmbacher L.L.C. HVAC
    NJ Master HVAC Lic.
    Mahwah, NJ
    Specializing in steam and hydronic heating
  • icesailoricesailor Member Posts: 7,265

    Use reverse return. I wouldn't use parallel on different sized tanks.

    I've re-piped more than a few, done by others, that were uneven and in series, They worked better when piped as "balanced"
    than any other way. They even ran out together.

    The taller tank used the most hot water until both tanks were in thermal equilibrium. That was my experience. I did a lot of houses for a designer that was nuts, He wanted single 80 gallon electric water heaters in 40 inch (5 block) crawl spaces. I convinced him to let me put in two fo's that I didn't have to dig a hole to put them in, he had twice the recovery rate as a single 80 gallon heater, and the recovery was the same as a 4o gallon gas water heater.
  • hot_rodhot_rod Member Posts: 13,287
    Depends on the use, somewhat. We used series with vacation homes where the load changes with occupancy. Keep the first low, or vacation mode until the home fills up.

    I also see installers using balance valves, but I don't think that would work with different size tanks, same with reverse return.

    I think series might be a good option, under your conditions.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • Robert O'BrienRobert O'Brien Member Posts: 3,190
    edited March 2015
    With new DOE water heater regs taking effect next month,this is going to become much more common. No more conventional gas/electric tank type heaters over 55 gals
    To learn more about this professional, click here to visit their ad in Find A Contractor.
  • wogpa67wogpa67 Member Posts: 238
    I think we'll be seeing two smaller tanks more often after april.
  • SWEISWEI Member Posts: 7,356
    Time to prepare for a rash of common venting no-no's?
    Robert O'Brienkcopp
  • wogpa67wogpa67 Member Posts: 238
    Oh I need to find a pic from 2 years ago. A classic.
  • Bob Bona_4Bob Bona_4 Member Posts: 2,083
    And they are physically bigger too with new DOE required insulation. Got to watch those tight replacements.
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