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New home with 300 gallon tub and small radiant heating load

solradmansolradman Posts: 47Member
Looking at a job that will have a 300 gallon soaking tub and a heating load of 37,551 Btu's. Home will have radiant floors and plan is to using a mod-con boiler. Would a 199,000 Btu boiler and 80 gallon indirect be better than a couple tankless units just for the bathroom with tub. Thinking the tub will need 250 gallons as fast as possible. Any recommendations?


  • Robert O'BrienRobert O'Brien Posts: 3,095Member
    Separate the DHW and heating loads
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  • Larry WeingartenLarry Weingarten Posts: 1,459Member
    Hello, Any chance they would go for a smaller capacity tub? If so, you could combine systems. Looking on-line, I see 60 gallons for deep soaking tubs. 300 is a lot! If they are inflexible, I'd look at tankless units jut to serve that tub. You're probably looking for at least 5 gpm at a 90 degree rise for half of the water. That's 25 minutes to fill!

    300 gallons could be OK if the water were treated and the tub stayed full, like a hot tub. :#

    Yours, Larry
  • EBEBRATT-EdEBEBRATT-Ed Posts: 5,617Member

    Where I come from that's not a soaking tub it's a swimming pool!

    If they have the $$$$ for that they have to have the $$ for the water heater to feed it.
  • ZmanZman Posts: 4,807Member
    300 gallons is a big tub. I have never seen one that big without it's own heater.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • bob eckbob eck Posts: 849Member
    Two 199,000 tankless has water heaters will give you about 11 GPM
    RINNAI makes a demand duo 199,000 tankless on a 119 gallon storage tank. They now have two 199,000 tankless on a 119 gallon tank.
    Vaughn has 119 gallon indirect water heater that you can get two coils in it.
    Check those options out.
    How many times are they going to fill a 300 gallon tub?
    Is this on a municipal water system or on a private well?
    If on a private well system what how many GPM does the well pump produce. If the well pump only pumps 7 gallon per minute that is all you are going to get.
    If on a well system do they have their own septic system that 300 gallons dumping into a older septic system can cause problems.
  • Solid_Fuel_ManSolid_Fuel_Man Posts: 1,454Member
    Tankless shines in this example. I agree with Bob eck, two will give better results. Will this place have a private sewer and well, or municipal?
    Master electrician specialising in boiler and burner controls, multiple fuel systems, radiant system controls, building controls, and universal refrigeration tech.
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