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Forced air hot water supply temp requirements

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Tonerlow
Tonerlow Member Posts: 85
What kind of supply temp is required for an air handler such as a Reznor WS23/33. When using in floor heat in a heated slab, will this unit add supplemental heat in cold areas using the same supply temp as the in floor heat tubing?

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  • Ironman
    Ironman Member Posts: 7,400
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    That would require you to calculate how much supplemental heat you need and then compare that to the manufacturer’s performance data for their appliance at that SWT.

    Practically speaking, the low SWT (75-105*) used in a radiant slab, is probably too low for a fan coil which usually has a minimum requirement of 120* SWT.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • hot_rod
    hot_rod Member Posts: 22,505
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    Here are some formulas and graphs for example. If you can find the manufacturers spec sheet, better yet.

    At some temperature the air coming out may be uncomfortably cool. Still slowly adding heat, but not exactly the hot air feel air to air heat pumps are known for blowing “Luke warm” air under low ambient conditions.

    Increasing the water flow rate can add a bit of output also. Heat can in fact jump off a faster moving flow rate. That is often shown in the manufacturer spec also
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,849
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    Supply air under 90-100 will feel cool or cold and it depends on the velocity of the air as well. I would think water below 115-120 would be an issue
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,176
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    Tonerlow said:

    What kind of supply temp is required for an air handler such as a Reznor WS23/33. When using in floor heat in a heated slab, will this unit add supplemental heat in cold areas using the same supply temp as the in floor heat tubing?

    NO!

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

    bburd
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,176
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    Here are the numbers
    Radiant floor heat max water temperature = 120°F
    Heating capacity of Reznor WS23/33. is based on 2PSI steam pressure
    That is equal to water temperature near 215° to 220°
    The conversion factor for the BTU output of the Reznor WS23/33 with 120° entering water temperature and 60° entering air temperature is .385.
    Using the rated capacity of 33,000 BTUh and the conversion factor of .385 you would get a heating capacity of 12,705 BTUh
    Will that be enough supplemental heat?
    Will you need to set the thermostat to 74° to compensate for the blowing cold air from the Reznor WS 23/33?

    The cold air that will be moving past the coil into the space will make the room temperature of 68° feel like 58° (like wind chill). That will defeat the whole purpose of the comfort of radiant floor heat.

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

  • hot_rod
    hot_rod Member Posts: 22,505
    edited January 2023
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    What about adding some radiant ceiling supplement? I’ve done it in a few shops with copper tube snapped into heat transfer plates

    One body shop had a metal ceiling, so the entire metal turned into a low temperature emitter

    my last home had PAP tube in thermofin on the ceiling. Exposed!

    with radiant ceiling you have a lot of square footage to build a massive radiator

    Run through the floor first, then through the ceiling to really drop the return temperature and boost boiler efficient 

    The key would be to determine how much supplemental heat you need to provide

    although with 100 SWT to the Reznor you still get some output. I assume this is a shop?

    Although I despise propeller fan noise🤨
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    EdTheHeaterMan
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,176
    edited January 2023
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    I agree about propeller fan noise also @hot_rod ... But it was funny to see a Boeing 707 Airliner in the movie Airplane with Prop Plane background noise.

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

    pecmsgJUGHNE
  • Hot_water_fan
    Hot_water_fan Member Posts: 1,922
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    Cooler air is fine if the blower can turn down its CFM - 140 F blow at triple the velocity isn’t all that warm 
  • hot_rod
    hot_rod Member Posts: 22,505
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    I agree about propeller fan noise also @hot_rod ... But it was funny to see a Boeing 707 Airliner in the movie Airplane with Prop Plane background noise.
    Roger, Roger
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    EdTheHeaterMan
  • Tonerlow
    Tonerlow Member Posts: 85
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    @hot_rod We have this issue in our shop at work yes. We are going to have a proper mixing valve installed and the boiler reprogrammed to provide the 2 separate supply temps for air handler and radiant slab heat. 

    I also serve on town council and our rink (built mid 90s) has some cold spots. There are 3 Viessmann boilers providing in floor heat throughout. The dressing rooms right now have 240v electric heaters that have been added for supplemental heat. We are discussing cost effective ways to get gas heat into this space rather than electric. One suggestion was the unit heaters, but I was unsure if these would serve much benefit, as I think installing the proper mixing valves and other instrumentation would prove to cumbersome in this large building. That’s why I was wondering about their performance at low supply temps. 
    My personal opinion is that we should run gas down the hallway and install a small natural gas forced air heater in each dressing room, but as stated we are looking for the most cost effective way to remedy this situation. 

  • hot_rod
    hot_rod Member Posts: 22,505
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    Tonerlow said:

    @hot_rod We have this issue in our shop at work yes. We are going to have a proper mixing valve installed and the boiler reprogrammed to provide the 2 separate supply temps for air handler and radiant slab heat. 


    I also serve on town council and our rink (built mid 90s) has some cold spots. There are 3 Viessmann boilers providing in floor heat throughout. The dressing rooms right now have 240v electric heaters that have been added for supplemental heat. We are discussing cost effective ways to get gas heat into this space rather than electric. One suggestion was the unit heaters, but I was unsure if these would serve much benefit, as I think installing the proper mixing valves and other instrumentation would prove to cumbersome in this large building. That’s why I was wondering about their performance at low supply temps. 
    My personal opinion is that we should run gas down the hallway and install a small natural gas forced air heater in each dressing room, but as stated we are looking for the most cost effective way to remedy this situation. 

    Bummer that you cant use some more from the Viessmanns somehow?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Ironman
    Ironman Member Posts: 7,400
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    What’s heating the domestic?
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • lkstdl
    lkstdl Member Posts: 41
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    Why not panel rads? Too much physical abuse?
    Luke Stodola
  • Tonerlow
    Tonerlow Member Posts: 85
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    @lkstdl never considered that. Maybe access to the piping is an issue, I’m not sure, I will inquire.