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Hot Water Tank Temperature

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06honda
06honda Member Posts: 15
in Radiant Heating
I had a new natural gas direct power vent hot water tank installed to work with my infloor radiant heating system. On my old one it was hard to tell the temp due to it being a 18 year old tank with a dial type. This one is light controlled, I had it set a 120 but bumped it up to 125 this evening. My understanding is the floor temp for the system is around 115. Just wondering if the HWT temp should be around that or a little higher. No kids in the house so me and the wife are aware of being careful turning on showers etc. Very small house, one level 1080 sq feet. Thanks for any info.

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  • kcopp
    kcopp Member Posts: 4,432
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    Was there a heatloss done to figure out the heat load? Is this staple up in the floor joist or in a slab? Why not a boiler instead of a water heater?
  • 06honda
    06honda Member Posts: 15
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    I am not the original owner of the home so as it was professionally installed by a plumbing contractor back in 1999 my guess is they would have done a heatloss. No idea what it is. The system is on slab. I simply replaced the Natural Gas Direct Power vent hot water tank with the same type.
  • Gordy
    Gordy Member Posts: 9,546
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    Does this tank water heater only service the radiant?
  • hot_rod
    hot_rod Member Posts: 22,157
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    Sounds like you have a combined DHW/ radiant system. The temperature for the radiant, if you don't have a design, will need to be set high enough for your coldest day condition.

    Ideally the system would be separate from the DHW and the temperature supplied to the radiant could be modulated based on outdoor temperature.

    You have a bit of a compromise system and will need to experiment with temperatures. However the tank also needs to be set to provide adequate DHW when there is no heating loads.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    06honda
  • 06honda
    06honda Member Posts: 15
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    "Does this tank water heater only service the radiant? " it provides water to the entire house including heating.
  • kcopp
    kcopp Member Posts: 4,432
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    Its an "open" system... less than ideal.
    All that stagnant water out under the floor coms back to the water heater when first turned on.
    A water heater was not a great choice....

    To your original question 120-125 should be fine.
  • Gordy
    Gordy Member Posts: 9,546
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    Separate the two systems with a heat exchanger. This keeps hydronic heating water out of your domestic water.

    Legionella becomes a big concern when running tank temps that low.
  • 06honda
    06honda Member Posts: 15
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    Thanks for the input, your right open system not the best but costs me about $100-$130 per month to heat the place. I will keep the tank in the 120-125 range. The plumber wanted me to install a tankless setup but the cost was crazy.
  • Jamie Hall
    Jamie Hall Member Posts: 23,313
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    Normally I am opposed to regulation, but...

    I simply cannot understand why the plumbing codes permit open systems like that. A health hazard beyond comprehension...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    Canucker
  • kcopp
    kcopp Member Posts: 4,432
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    I don't like them but you prob have a higher chance of being killed or hurt driving than having one of these systems in. If he knows the risks its on him... sign a waiver
  • 06honda
    06honda Member Posts: 15
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    I guess that was the way they installed them back in the late 90's. There are about a dozen or so homes in our area with the same setup.

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