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Thread: New Install Help Please

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  1. #1
    DIY Junior Member Greatwhitewing's Avatar
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    Default New Install Help Please

    In the springtime had installed Viesmann Vitronic 100 and Superstor 45 gallon indirect water heater. Shower is delta Carlisle rated at 2.5 + 2.5 GPM. Water heater on priority zone. Boiler has outdoor reset setback controls. Installed by very reputable contractor. Oil fired. WH was set to 130 and boiler temp varies.

    First shower of 20 minutes with flow throttled back approx 60-70% of max flow and runs out of hot water and have to turn temperature ALL the way up. No other loads on DHW.

    Had NONE of these issues during the summer months, plenty of hot water. Now the boiler is running for heat we have the shower problem. Had shower temp set in the middle at all times no matter how long the shower.

    I was assured this set up would supply plenty of water unless really hot and really long showers back to back.

    The contractor came by and made some adjustments with little or no change in performance.

    Any ideas what to discuss with installer? This is not much better performance than I had with a 20 year old tankless POS.

  2. #2
    Engineer Furd's Avatar
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    Your description is a bit confusing.
    Shower is delta Carlisle rated at 2.5 + 2.5 GPM
    Do you mean you have TWO shower heads and each is rated at 2-1/2 gallons per minute?

    If so, then THAT is the problem. A tank-type water heater can supply roughly 70% of its ultimate capacity before a noticeable drop in temperature occurs. That would mean that you have roughly 30 gallons of 130 degree water with it being cooled by the incoming water when in use. At 60% (of 5 gpm) flow rate you are using about 3 gallons per minute. Assuming that you are also mixing about 30% cold with the hot at the shower gives you an approximate flow rate of 2.1 gpm out of the water heater. That would be about 42 gallons in 20 minutes. Of course the heating supply from the boiler is going to offset the temperature drop from the tank somewhat but not likely enough to allow such flow rates for 20 minutes, especially if you do not have a priority control that (a) turns off space heating when using significant amounts of hot water, and (b) allows the boiler temperature to rise to full cut-out temperature; in other words, does not limit boiler temperature according to outside temperature.

    The first thing I would do is to install a priority control (if you do not presently have such) and then raise the temperature of the heater to a minimum of 140 degrees (160 may be necessary) AND install a tempering valve at the water heater outlet to supply 130 degree maximum temperature water (125 may be safer) to the house plumbing. Starting with a higher temperature in the tank allows for more dilution with cold and reduces the flow rate out of the tank giving an effect of more hot water.

  3. #3
    Retired Defense Industry Engineer jadnashua's Avatar
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    An indirect normally is setup with the boiler as a primary zone - this means that when it needs heat, it gets ALL the heat from the boiler. If so, then the thing should be setup to run full-fire, max temp to heat and reheat the indirect. Based on the size of the boiler and the size of the tank, the spec sheet should give you the first hour use. A properly setup indirect will normally provide LOTS more hot water than the equivalent sized self-contained unit (say NG, or electric), since the boiler has LOTS more BTU output than a typical WH.

    Where I live, they REQUIRE a tempering valve on the outlet of any WH, regardless of how it is heated. With an indirect, they are normally rated to be set to maintain 140-degrees, and higher can be used, but anything above 120 should have a tempering valve to restrict the outlet to that. An exception is things like the dishwasher and washing machine which can clean better with hotter water (at least the DW, many people don't use hot in their WM).
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  4. #4
    DIY Junior Member Greatwhitewing's Avatar
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    I wasn't quite sure how to interpret that 2.5 spec listed twice. Maybe someone who knows for sure can chime in. Bottom line is the flow is throttled pretty far back to to 50-75% of max flow.

    The HWH is on the priority zone. Guy said it wasn't when he came but the initial install guys said it was. Not sure what to believe.

    I have a tempering valve installed already.


    Quote Originally Posted by Furd View Post
    Your description is a bit confusing. Do you mean you have TWO shower heads and each is rated at 2-1/2 gallons per minute?

    If so, then THAT is the problem. A tank-type water heater can supply roughly 70% of its ultimate capacity before a noticeable drop in temperature occurs. That would mean that you have roughly 30 gallons of 130 degree water with it being cooled by the incoming water when in use. At 60% (of 5 gpm) flow rate you are using about 3 gallons per minute. Assuming that you are also mixing about 30% cold with the hot at the shower gives you an approximate flow rate of 2.1 gpm out of the water heater. That would be about 42 gallons in 20 minutes. Of course the heating supply from the boiler is going to offset the temperature drop from the tank somewhat but not likely enough to allow such flow rates for 20 minutes, especially if you do not have a priority control that (a) turns off space heating when using significant amounts of hot water, and (b) allows the boiler temperature to rise to full cut-out temperature; in other words, does not limit boiler temperature according to outside temperature.

    The first thing I would do is to install a priority control (if you do not presently have such) and then raise the temperature of the heater to a minimum of 140 degrees (160 may be necessary) AND install a tempering valve at the water heater outlet to supply 130 degree maximum temperature water (125 may be safer) to the house plumbing. Starting with a higher temperature in the tank allows for more dilution with cold and reduces the flow rate out of the tank giving an effect of more hot water.

  5. #5
    Retired Defense Industry Engineer jadnashua's Avatar
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    Raise the WH set temp to say 140-degrees and see what happens. You may want to lower the tempering valve setting to something around 120-degrees to prevent potential scalding issues. Also, the tempering valve may not be working well...it could be mixing in more cold than it should, masking that the tank really does still have hot water in it. While the water is being used, you might want to compare the pipe temp on the inlet and outlet of the tempering valve. Once the tank's temp drops below the setting of the tempering valve, it should not be mixing in any cold water and the inlet (hot) and outlet (tempered) should reach the same temperature. That info is probably available in the boiler's controller, but may be harder to find.

    To check if it is a priority zone, one way would be to wait until one or more heating zones are calling for heat, then while that's still happening, exhaust the water tank to see if they stop getting heat. You may need to raise the room's thermostats temporarily to ensure they would still be calling for heat while the tank then needs it.

    Also, ensure that the temperature sensor on the tank is inserted ALL the way into the well of the indirect...it is only held in by a spring clip, and may not be accurately sensing the temperature.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  6. #6

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    A zone controller with a DHW Priority would help greatly. Check out Taco's ZVC series.

    As mentioned above, increase the water temperature. You want 130 at the tap, which will require 140-160 in the tank.

    Finally, what size copper did the plumber use to pipe the HWH to the boiler? As a minimum it should be 1". If the plumber used 3/4 it will almost double the time for the HWH to recover.

  7. #7
    In the trades Dana's Avatar
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    You can measure your actual flow out of the showerheads with a bucket, a stopwatch and a measuring cup. Turn it on, put the bucket under it for exactly 30 seconds, then use the cup to measure how much water was in the bucket. A 2.5gpm head usually delivers between 1.8-2.2gpm unless you have unusually high water pressure.

    A 20 minute shower is a bit on the long side. Not sure if simply cranking the temp is going to buy you much. Even the smallest oil boiler is going to be putting out 60KBTU/hr, which should be able to keep up with an endless shower if it's cut back to under 1gpm per head as-described. With 45F incoming water, 105F shower exit temp at a total 2gpm you're ~70KBTU/hr.

    If the boiler's outdoor reset isn't set up to be over-ridden by the priority demand, and the boiler's output is held to a relatively tepid 150F because it's not very cold outside there may not be a big enough delta-T on the heat exchanger inside the SuperStore to deliver that much heat and the boiler will be cycling on/off during the shower even as the temp in the tank falls.

    What's the BTU, gph, or kilowatt rating of the Viessmann?

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