Announcement

Collapse
No announcement yet.

Water Heaters in Series vs. Parallel

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Water Heaters in Series vs. Parallel

    Please enlighten me. When connecting two water heaters I have always connected them in series thinking I would get the maximum output. And if the homeowner wants to pay a little extra I install a bypass and extra ball valves in case one or the other tanks leaks so it can be isolated. Lately I have come across several installations where the tanks were connected in parallel. I have always considered this a less efficient way of connecting them. It seems the piping exiting the tanks and before they join would have to be exactly the same lengths or else one would deplete quicker than the other thus mixing cold with the remaining hot. Also, the interior pipe dynamics would probably be an issue correct? I mean, if there were any kind of restrictions such as check valves or heat traps (especially if the tanks are not the same brand due to one of them already having been replaced), or eddies and cavitations in a section of pipe that wasn't reamed, would that cause them to be out of balance?
    "Man will do many things to get himself loved, he will do all things to get himself envied." Mark Twain

  • #2
    I too prefer series over a parallel connection. typically set the inlet heater to 100 and the outlet heater to 130-135. this way both heater have approx the same 30-35 degree rise. A simple fix if 1 heater takes a dump and no big deal if the first inlet heater is just a storage tank, if the unit doesn't stay lit.

    Rick.
    phoebe it is

    Comment


    • SlimTim
      SlimTim commented
      Editing a comment
      If there was a high demand for hot (shower hot) water would the outlet tank have time to raise the water from the inlet tank 30 degrees?

  • #3
    Rick with your setup don't you end up with a the first WH storing water at less than 110?. Isn't that the optimum temp for legionella to exist or multiply?

    https://en.wikipedia.org/wiki/Legionella#Heat
    • At 50 C (122 F) – 90% die in 80–124 minutes, depending on strain (D = 80–124 minutes)
    • 48 to 50 C (118 to 122 F) – can survive but do not multiply
    • 32 to 42 C (90 to 108 F) – ideal growth range
    • 25 to 45 C (77 to 113 F) – growth range
    • Below 20 C (68 F) – can survive, even below freezing, but are dormant
    Last edited by Bob D.; 03-21-2020, 06:56 AM.
    "It's a table saw, do you know where your fingers are?" Bob D. 2006

    https://www.youtube.com/user/PowerToolInstitute

    https://www.youtube.com/channel/UC1p...qcZKHyrqKhikFA

    ----

    Comment


    • #4
      Bob, if this was an issue, every source of water would be an issue. We would all know people who were infected by this. Every tankless heater would be a source as by default the water is set to below 125. Both hot and cold water would have to be maintained at ideal temperatures. Because at any given time water is at the ideal temperature in both our hot and cold potable systems. Also the disease is a respiratory infection in the lungs. so unless you aspirate liquids or use humidifiers that you breath in contaminated liquids, you're not going to get it. The original outbreak was in 1976 at a hotel in Philadelphia attended by veterans for the bicentennial.


      From Wikipedia

      Airborne transmission from cooling towers[edit]


      The largest[26] and most common source of Legionnaires' disease outbreaks are cooling towers (heat rejection equipment used in air conditioning and industrial cooling water systems) primarily because of the risk for widespread circulation. Many governmental agencies, cooling tower manufacturers, and industrial trade organisations have developed design and maintenance guidelines for controlling the growth and proliferation of Legionella within cooling towers.


      Legionella species typically exist in nature at low concentrations, in groundwater, lakes, and streams. They reproduce after entering man-made equipment, given the right environmental conditions.[citation needed] In the United States, the disease affects between 8,000 and 18,000 individuals a year.[15]

      Chlorine
      A very effective chemical treatment is chlorine. For systems with marginal issues, chlorine provides effective results at 0.5 ppm[citation needed] residual in the hot water system. For systems with significant Legionella problems, temporary shock chlorination—where levels are raised to higher than 2 ppm for a period of 24 hours or more and then returned to 0.5 ppm—may be effective.[citation needed] Hyperchlorination can also be used where the water system is taken out of service and the chlorine residual is raised to 50 ppm or higher at all distal points for 24 hours or more. The system is then flushed and returned to 0.5 ppm chlorine prior to being placed back into service. These high levels of chlorine penetrate biofilm, killing both the Legionella bacteria and the host organisms. Annual hyperchlorination can be an effective part of a comprehensive Legionella preventive action plan.[31]

      Pulled from our 2018 ladwp water quality report.

      mg/L = milligrams per liter (equivalent to ppm) Chlorine Residual,
      Total Drinking water disinfectant added for
      treatment mg/L YES (4) (4) HRAA = 2.0 (a) Range = 1.8 – 2.1

      I guess in a laboratory anything can be grown, but in reality we have safe drinking water. Not sure why some of our locals are clearing the shelves and buying bottled water. Of course Toilet paper is a case by case scenario. no pun intended.

      Rick.
      phoebe it is

      Comment


      • #5
        "Bob, if this was an issue, every source of water would be an issue."

        That's the point, every source of water IS an issue.

        You know I respect your years of experience and great depth of knowledge on all things related to plumbing Rick, but on this I have and still do disagree with you. And I'm in good company as evidenced below with these snippets of information from just two of hundreds of agencies and companies who also feel water heaters can pose a risk if the water temperature is not hot enough to kill the Legionella bacterium.

        The ASSE says (see attachment or use link below) on page 11 of a white paper titled:

        "Recommended Installation Practices for Residential Storage
        Type Water Heaters to Reduce the Danger of Scalds"

        https://www.asse-plumbing.org/media/...hite_paper.pdf


        #3 – All water heaters, new installation or replacement, must be installed per the manufacturers’ installation instructions or the prevailing codes, whichever is more stringent.
        When a water heater is not properly installed including verifying the required temperature settings of the downstream temperature control devices, the potential for scald injuries is dramatically increased.

        It is recommended that in all scenarios, to help reduce the danger of scald burns from extremely hot water at the point of use, to install a Temperature Actuated Mixing Valve for Hot Water Distribution Systems compliant to ASSE 1017 at the hot water source, the water heater. This will allow the water heater thermostat to be set at a higher temperature, which accomplishes two additional benefits:

        - Increases the available amount of hot water and
        - Controls the growth of legionella bacteria in the water heater.

        The ASSE 1017 device at the outlet of the water heater then can be set to the industry recommended maximum temperature of 120? F to control the hot water system temperature. The accuracy of an ASSE 1017 listed device, for a typical residence, flowing a total of less than 5 gpm will control the outlet water temperature within plus or minus 3? F based upon the performance requirements of the standard.

        Installing an ASSE 1017 Temperature Actuated Mixing Valve at the water heater does not replace or negate the requirement of point of use temperature limiting devices at showers, tub/shower
        combinations, whirlpool bathtubs, soaking tubs, etc.

        #4 – The most effective way to control the potential increase in water temperature in the hot
        water distribution system due to the Stacking Effect is to install a Temperature Actuated
        Mixing Valve listed to ASSE 1017 at or near the water heater.
        ---snip---


        For anyone who doubts me, just do a quick google search on

        'how hot should your water heater be to be safe from legionella'


        Three examples from that search:

        https://www.cdc.gov/legionella/wmp/o...nd-spread.html

        ---snip---
        Where Legionella Can Grow or Spread
        Legionella can grow in many parts of building water systems that are continually wet, and certain devices can then spread contaminated water droplets. Some examples of devices where Legionella can grow and/or spread through aerosolization or aspiration (when water accidentally goes into the lungs while drinking) include:

        - Hot and cold water storage tanks
        - Water heaters
        - Showerheads and hoses
        - Centrally installed misters, atomizers, air washers, and humidifiers
        - Non-stream aerosol-generating humidifiers
        - Infrequently used equipment including eyewash stations
        - Ice machines
        - Hot tubs
        - Decorative fountains
        - Cooling towers
        - Medical equipment (such as CPAP machines, hydrotherapy equipment, bronchoscopes)
        ---snip---

        ---snipped from treehugger.com---
        Hydro Quebec, (admittedly an electric utility)

        To reduce the risk of burns from hot tap water, the temperature setting on the water heater can be turned down. But if the temperature is set too low, bacteria may begin to grow in the tank. Even at 60 ?C – the setting on most electric water heaters – an estimated 25% of all water heaters are contaminated by legionella bacteria.

        Legionella bacteria tend to grow in the lower temperatures at the bottom of water heater; such bacteria can cause a form of pneumonia. The organism is generally transmitted when people inhale contaminated water droplets from whirlpool baths, showers or building air conditioning systems. In Qu?bec, about 100 people a year are hospitalized for pneumonia caused by contaminated residential water heaters.

        In light of the statistics, it is not advisable to lower the water heater temperature to, say, 49? C. This would not only reduce the hot water supply by some 20%, it would also put your household at risk of contracting pneumonia.
        ---snip---


        Now having said all that I am certainly aware that millions of WHs are set at less than 135 and all those people have not contracted the disease or died. I also acknowledge the risk that this temperature presents with kids or elderly in the home, and even to adults for that matter. I don't deny that millions of people have cheated death by keeping the WH temp below 135F.


        So I'll keep my WH at 140, and use anti-scald devices were needed. Everyone can (and will) do as they wish, you all know the risk, and no one is coming to stick a thermometer in your water heater. I just want those who read this thread down the road to know both sides of the story.


        Attached Files
        "It's a table saw, do you know where your fingers are?" Bob D. 2006

        https://www.youtube.com/user/PowerToolInstitute

        https://www.youtube.com/channel/UC1p...qcZKHyrqKhikFA

        ----

        Comment


        • #6
          However, it does make and excellent scare sales tactic. Think of all the mixing valve installation, maintenance and calibration I can do! I (of course ) would never do this, but if I just casually mentioned the possibility of catching pneumonia from their water heater they would lose sleep until I resolved the issue. Seriously though, I didn't know a lot of the information you both shared. I always like to increase my knowledge so it looks like I know what I'm talking about. Thanks so much.
          "Man will do many things to get himself loved, he will do all things to get himself envied." Mark Twain

          Comment


          • #7
            Once again if you aspirate, you technically get pneumonia. It's not about drinking the water, it's about inhaling the water into your lungs.

            Didn't you see the snippet of chlorine and ppm. .5 ppm is all you need to kill it. We have 1.8-2.0 ppm in LA water. Must not be an issue out here. It if was, we would see tempering valves at every heater both commercial and residential. So far I only see them on commercial kitchens when they are using them for dishwashers and public restrooms.

            What do you do about the cold water in the summer time. Or storage tanks?

            It's all chlorinenated out her. Like I said, if it were an issue out here, we would all have tempering valves. Supply house would be selling them. Other than public restrooms that allow 105 max. I rarely see 1. Possibly 1 a year if I'm lucky.

            Might be different in other parts of the country and areas with well water. But with 4 million in city or LA. We don't have the issue. And the gas co always turns the heater down to 125 or less.

            We have a pandemic of a different source. Never heard of an epidemic of leginela other than the one during the 1976 incident that the disease was named after.

            ​​​​​​I guess I'll just have to take the chance that me and thousands of other plumbers in LA are not causing an outbreak of leginela disease.

            Rick.
            phoebe it is

            Comment


            • Bob D.
              Bob D. commented
              Editing a comment
              So why do all these organizations make these claims? They are saying that daily activities like showering can aerosolize the bacterium. Is it only to sell product and no one has challenged them on it. What do they have to gain.

              Yes, where I am over half the population of my county has well water. Only 3 of 21 municipalities have public water and sewer systems. So about half do not have chlorinated water. It's the boonies in comparison to LA or any other metropolitan area. But much of the country is that way.

            • PLUMBER RICK
              PLUMBER RICK commented
              Editing a comment
              Bob, I think you hit it. While we have municipal treated water, that's chlorinated, your region has private well water for the most part that's not chlorinated.

              I guess since we don't deal with the water chemistry on an individual basis, we don't have to concern ourselves about a disease that is out of our control. Especially when it's more of an hvac airborne disease than a portable water issue.

              Cooling towers are the ideal breeding ground for this. The evaporative mist that's discharged into the air is of greater concern. Since I'm not an hvac person, I don't have first hand experience on how they treat or maintain their equipment to inhibit the growth.

              We both have experience in the trades. And both concerns over the safety of our water. But we are dealing with different parts of the country. Fortunately our municipality takes the guess work out of our water safety.

              Now if the world health professionals can put their minds together and solve our present Coronavirus crisis, we can get back to our normal as we know it.

              Rick.

          • #8
            Per Mfg's Installation Directions they Recommend a Parallel Connection, this gives double the storage and double the Burner Recover with both burners running at the same time,
            Former Mfg's Service Agent for all National Mfg's for over 30 years
            JERRYMAC
            E-MAILJERRYMAC777@GMAIL.COM
            CALIF. LIC. PLBG,HEAT,DRAINS,ELECTRIC,WATER HEATER, BOILER, POOL AND SPA HEATER
            FIRE SPRINKLER CONTRACTOR,
            SINCE JAN. 1989

            Comment


            • PLUMBER RICK
              PLUMBER RICK commented
              Editing a comment
              But if you pipe the return line into the first heater, in reality the first heater is pretty much up to temperature of the second heater. Minus any heat loss in the return loop. Which in my case is minimal out here.

              Rick.

            • Bob D.
              Bob D. commented
              Editing a comment
              So the second WH ends up maintaining temp in both tanks, and the heating element (or burner) on the first only operates when there is demand. Did I get that right?

          • #9
            That sounds like what he is saying Bob D. My next question is, If a water heater comes with heat traps in the inlet and outlet doesn't that make it a closed vessel and it will open the relief valve every time it heats? We don't have check valves in the water meters here so normally the pressure backs up into the street.
            "Man will do many things to get himself loved, he will do all things to get himself envied." Mark Twain

            Comment


            • PLUMBER RICK
              PLUMBER RICK commented
              Editing a comment
              Heat traps don't fully stop water flow like a check valve.
              Technically As long as you're city pressure is below the relief valve opening and your pressure regulator allows for thermal expansion and there's no check valves in the system or meter, yes the pressure will go back out to the city main. Pretty much how ours does out here .

              Some regulator brands don't allow for thermal expansion.

              Rick.

          • #10
            Gonna be honest didn't read everything in this post...but this is the way we do it in parallel, eliminates the need for the pipes to be exactly equidistant apart with exact same amount of piping. You can do 2+ this way and it works for parallel piping AND everything is isolated in case of failure.


            Comment


            • PLUMBER RICK
              PLUMBER RICK commented
              Editing a comment
              Yes, first heater, cold in first and out last.
              last heater, cold in last and hot out first.

              In theory that makes the piping similar lengths. so long as the fittings and friction loss is similar. but heaters with heat trap nipples don't always flow the same rates. especially when water hardness and rust comes into play.

              With series there's no worries with piping length or friction loss as the secondary heater is controlling the outlet heat and delivery.

              If the first (inlet) heater goes out, you just loose hot water capacity when there is no circ pump. if you have a circ pump, then all you loose is the hot water recovery time, but still retain the 2 heaters original storage. sort of like a very large return line storage capacity.

              If the second (outlet) heater goes out. with no circ line, you loose initial hot water delivery, but eventually will get hot from the first heater. with a circ pump, you will loose your higher temperature, but will still have the volume of both heaters assuming that the heaters are staged different temperatures.


              Rick
          Working...
          X