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  1. #1
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    Default tankless water heater radiant heat

    This Rinnai RC98 served hot water & radiant heat for a 1,500 sf TH. min gas btu input 9,500. Is this enough for this home hot water & heat?

    What should be paid attention to on this installation? IS Rinnai cheap only $1000 ? How is the quality? First time seeing this.

    Thank you

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  2. #2
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    Default Re: tankless water heater radiant heat

    Are you sure the BTU wasn't 95,000? Tankless can be used for radiant floor. Like anything the supply temp has to be set right. Did the house warm up?

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  3. #3
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    Default Re: tankless water heater radiant heat

    Quote Originally Posted by Robert Ernst View Post
    Are you sure the BTU wasn't 95,000? Tankless can be used for radiant floor. Like anything the supply temp has to be set right. Did the house warm up?
    Sorry, it is 95,000 BTU/H, actually Max is 139,000 which I cannot get a clear view. Certainly, 4 zones all warmed up. I was wondering how it could be once washer is on while showering at the same time in the cold winter, let us say -10 outside. This unit does have a priority button. I figured hot water supply & pressure is prior to the flow to radiant heat, right?

    This unit is only about $1,600 and has 12yrs warrenty. if that is true, I believe it will dominate market very soon.


  4. #4

    Default Re: tankless water heater radiant heat

    Quote Originally Posted by Peter Louis View Post
    Sorry, it is 95,000 BTU/H, actually Max is 139,000 which I cannot get a clear view. Certainly, 4 zones all warmed up. I was wondering how it could be once washer is on while showering at the same time in the cold winter, let us say -10 outside. This unit does have a priority button. I figured hot water supply & pressure is prior to the flow to radiant heat, right?

    This unit is only about $1,600 and has 12yrs warrenty. if that is true, I believe it will dominate market very soon.
    You can expect to pay another $1500-$2000 to have a plumber install it.

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  5. #5
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    Default Re: tankless water heater radiant heat

    Peter,
    Unless you take 3 or 4 hour showers several times a day while you do 10 loads of laundry per day the down time of the heating should not have that great of an effect. That is providing there are enough BTUs to heat the house. One thing to think about is longevity of system. The heating system will have more duty cycles if used for heating. So the question is, how many duty cycles does the heater have before it has to be replaced. Same rational as heat pumps not lasting as long (in years) as a dedicated furnace and AC system.


  6. #6
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    Feb 2008
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    Default Re: tankless water heater radiant heat

    Its critical to know the incoming temp of the water supply from well or street and the temperature rise the unit can provide dependent on Btu and water flow through the unit (gallons per minute).

    Also the number of bathrooms, tubs, number of people in the house factor in to the equation.

    If the unit is not big enough they can put another condensing unit in series or use a storage tank, or even a electric or gas powered hot water heater which stores the heated water and keeps it hot for distribution.

    To know whether its properly sized there should have been a heat loss calculation done on the home.

    Also the depth of the tubing under the concrete floor can and will affect temp output and hopefully when the house was built they put foam board under the steel grid on which the tubing is anchored then the concrete poured on top, other wise there will be heat being transfered to the earth.

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  7. #7
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    Feb 2008
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    New York
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    Default Re: tankless water heater radiant heat

    Quote Originally Posted by Peter Louis View Post
    Sorry, it is 95,000 BTU/H, actually Max is 139,000 which I cannot get a clear view. Certainly, 4 zones all warmed up. I was wondering how it could be once washer is on while showering at the same time in the cold winter, let us say -10 outside. This unit does have a priority button. I figured hot water supply & pressure is prior to the flow to radiant heat, right?

    This unit is only about $1,600 and has 12yrs warrenty. if that is true, I believe it will dominate market very soon.
    Check with the manufacturer, I believe the warrenty changes when the system is used for heating.

    Steven Turetsky, UID #16000002314
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  8. #8
    Join Date
    Jul 2008
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    Utah
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    Default Re: tankless water heater radiant heat

    I find the plumbers tape that is supporting the expansion tanks kind of interesting.



    But using simple rule of thumb estimation I'd agree with others that the capacity is adequate.


  9. #9
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    Default Re: tankless water heater radiant heat

    Navien Condensing Tankless Sizing (NR/NP)
    -:- Navien America -:-

    RC98 models
    Rinnai America


  10. #10
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    BC Canada
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    Default Re: tankless water heater radiant heat

    Will this kind replace all the regular HW tank+boiler?

    Cost, space, maintenance all advantages as long as it properly sized.


  11. #11
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    Default Re: tankless water heater radiant heat

    Quote Originally Posted by Peter Louis View Post
    Will this kind replace all the regular HW tank+boiler?

    .
    Yes it will replace the boiler and tank but it is not unique or proprietary nor is it new.

    Despite all of the apparent advantages there are large disadvantages as well. If you lose the boiler you lose space heat AND domestic hot water. The delivery rate of domestic hot water is fairly low and would make multiple showers, clothes washing and dish-washing impractical.

    Still, it has it's place.

    Last edited by Rod Butler; 02-24-2012 at 01:12 PM.

  12. #12
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    Default Re: tankless water heater radiant heat

    Quote Originally Posted by Rod Butler View Post
    Yes it will replace the boiler and tank but it is not unique or proprietary nor is it new.

    Despite all of the apparent advantages there are large disadvantages as well. If you lose the boiler you lose space heat AND domestic hot water. The delivery rate of domestic hot water is fairly low make multiple showers, clothes washing and dish-washing impractical.

    Still, it has it's place.
    Yes, Possibly start from TH & Condo even small family homes.


  13. #13
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    Feb 2008
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    Default Re: tankless water heater radiant heat

    Good info here
    Staying out of hot water with your water heater: A Manufacturer's


    http://www.google.ca/url?sa=t&rct=j&...t8PEbA&cad=rja

    Recirc loops can prevent condensing gas heaters from actually condensing
    – Flue gas starts condensing at about 135 F

    Combi units –
    – As building envelopes become more efficient, the heating load becomes less than the hot water load, so higher input high efficiency water heaters have the capability of providing both space and potable water heating.

    Additional water usage by tankless at start-up
    – “Initiation cycle” takes 10 – 20 seconds, during which water is flowing and not being heated to useful temperature


  14. #14
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    Oct 2011
    Location
    Minneapolis, MN
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    780

    Default Re: tankless water heater radiant heat

    I was talking to a plumber about these earlier this week, and he was saying it's very important what the water quality is like, as they tend to get clogged easily and lose efficiency.

    The hangers on the expansion tanks look like they are resting on the plumbing and possibly bending it a bit? Doesn't seem like good practice.

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