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*** Rheem Hybrid Water Heater with 35 or 55gal indirect water heater

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mp_e46
mp_e46 Member Posts: 2
Hello,

I currently have Burnham V8 (PV84WC-TCWN) oil fired boiler with an external indirect Burnham stone lined 80 Gal water tank in CT. I have well water. The coil in the indirect tank has a leak and blows the pressure relief valve on the boiler. It’s located in a large unfinished walkout basement. Household between 4-6 people.

My goal is to cut down on the consumption of oil. Also the town I live in has one of the cheapest electric rates at 11c /kWh.
Looking to replace the water tank with a Rheem Hybrid water heater 80gal to use it as a pre-heater which would feed into a 35 or 50 gal indirect tank. I understand the recovery for Hybrid WH is no where compared to the indirect tank. I can get both of these tank at a decent price. The Hybrid WH would be use the heat generated by the burnham boiler for the heat pump operation especially in winter and the electric elements would kick in depending on the mode of the Hybrid WH. Also the Hybrid can heat the 80gal overnight and I can also have circulator which would turn on at scheduled time at night to push the water from hot side back into cold side of the Hybrid WH to even out the temp between the two tanks.

I would keep the Hybrid temp at 140F which would feed into the indirect tank with a temp control mixing valve on the output of the indirect to prevent scalding. The majority of the work would be done by the hybrid and the indirect would come on when the demand goes up.

Am I thinking this correctly? Ideally I wish there was a hybrid with built in indirect coils.

Thank you

Comments

  • MikeAmann
    MikeAmann Member Posts: 998
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    Ahhhh. No answer.
    This is/was a good question.
  • pecmsg
    pecmsg Member Posts: 4,949
    edited November 2022
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    How many people in this house that you're going to use 80 gals of 140° water?
    ethicalpaul
  • hot_rod
    hot_rod Member Posts: 22,467
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    You could use a plate HX as the boost, tied to the boiler, enabled when the Hp falls below 110 or so. The are some pre made DHW modules. The higher the temperature in ant DHW device, the more mineral precipitation. Above 140 will really scale DHW stuff quickly.

    I think Hp tanks have the coils wrapped around the outside of the tank, like the Rheem solaraide tanks.

    A dual tank or dual DHW arrangement would best leverage the tank. In combi tanks, you compromise the best efficiencies. When the boiler would heat the tank for example, the Hp loses its ability to contribute. That was. The trade off with solar tanks that had resistance elements or dual coils.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • ethicalpaul
    ethicalpaul Member Posts: 5,792
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    140 is very high. I had mine set at 130 for awhile but I've lowered it to 125 with no ill effect, and no running out of water.

    I would start simple and just hook up the 80 gallon heat pump water heater directly to your hot water line and see how it does.

    Set it on heat pump only mode and see how it does. If necessary you can use its internal resistance heater to recover faster, but try heat pump only mode first. 80 gallons is a lot of water.

    NJ Steam Homeowner.
    Free NJ and remote steam advice: https://heatinghelp.com/find-a-contractor/detail/new-jersey-steam-help/
    See my sight glass boiler videos: https://bit.ly/3sZW1el

    Larry Weingarten
  • pecmsg
    pecmsg Member Posts: 4,949
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    140 is very high. I had mine set at 130 for awhile but I've lowered it to 125 with no ill effect, and no running out of water. I would start simple and just hook up the 80 gallon heat pump water heater directly to your hot water line and see how it does. Set it on heat pump only mode and see how it does. If necessary you can use its internal resistance heater to recover faster, but try heat pump only mode first. 80 gallons is a lot of water.
    ASHRAE Recommends 140* for 1hour to kill Legionnaires 
  • JakeCK
    JakeCK Member Posts: 1,415
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    hot_rod said:
    You could use a plate HX as the boost, tied to the boiler, enabled when the Hp falls below 110 or so. The are some pre made DHW modules. The higher the temperature in ant DHW device, the more mineral precipitation. Above 140 will really scale DHW stuff quickly. I think Hp tanks have the coils wrapped around the outside of the tank, like the Rheem solaraide tanks. A dual tank or dual DHW arrangement would best leverage the tank. In combi tanks, you compromise the best efficiencies. When the boiler would heat the tank for example, the Hp loses its ability to contribute. That was. The trade off with solar tanks that had resistance elements or dual coils.
    Quick question, since hpwh's heat the water using lower temp coils over a larger surface area vs the electric elements and heat exchanger in gas models, are they less susceptible to limescale? Or is 140f still hot enough to cause an issue? 
  • hot_rod
    hot_rod Member Posts: 22,467
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    I think 140 is getting out if the comforts zone for those hpwh, without some help from the element   Extended run time and efficiencies probably drops.

    it really comes down to how you feel about potential, health threatening bacteria? 80 gallon tank of 180f water should cover most homes and families 

    It wasn’t all that long ago that manufacturers were limiting tanks to 120f!

    I have had customers that got along fine with 40 and 50 gallon electric tanks

    There really in no one solution fits all with DHW expectations 
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream