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Hydronic air handlers

Brad White_9
Brad White_9 Member Posts: 2,440
is another, based in Dallas, TX (as opposed to what now, Dallas, Ohio? He asked rhetrorically...).

Key to any hydronic air handling unit with low temperature water is the number of rows. If you can get at least three if not four rows, you are doing very well.

One row, definitely not; not enough retention time for air nor water. Two rows may make it, but four rows gives you a lot of options and flexibility with balancing especially if you are compelled to reduce your highest temperature.

You can even get six row coils; I designed one once and it works like a champ, taking in 135 degree water and sending it back below 100...


  • Hey all,

    I'm looking for info on hydronic air handlers like you'd see in garages, running off of a hot water system. In particular, I'm looking for output information related to water temperature, so I know what I can do if I want to tie one (or two, or three) into a low temp radiant system without adding a high temp demand.

    Anyone have any good links or contact people I can talk to?

  • Cosmo_3
    Cosmo_3 Member Posts: 845
    Modine, or Reznor

    These are the two companies I deal with. I am sure either one entered into the google search bar will get you somewhere.

    I remember doing that exact same thing on a past Vitodens job.

    If I find a link I will e-mail it to you, but I think getting on Modine's website should get you the info you need, I believe they had derating info there.

    Let me know if that helps

  • Mark_46
    Mark_46 Member Posts: 312
    Hi Brad

    I have to ask, because I am in the middle of looking at all this with my own systems. (Actually, I'm up to my eyeballs with questions and ideas). I've come to the conclusion that I will be left to tune and balance my systems by myself. I know what was and wasn't checked. (GPM, CFM, static pressure, boiler water temp, CO checks, leaks in the plenums, DHW not priority as requested, the list goes on and on. Turns out the installer was ONLY an installer. Anyway...

    You say 135 degree inlet temp. Where can you expect the temperature of the oulet air to be? Does it even matter? Lower water temp means lower air temp output, correct? Does this translate into longer cycle times to heat the space?

  • Hi Cosmo,

    I tried finding the info on the modine site and (hangs head in shame) I couldn't find it.

    However the Reznor site had very helpful info easily available, thank you!

  • Thanks for the info Brad, not being a big user of these units that is very helpful to know.
  • Brad White_9
    Brad White_9 Member Posts: 2,440
    HW Temperature depends on a lot of things...

    Hey Mark-

    The 135 temperature was what was available for me to work with. The final air temperature almost does not matter so long as it heats the space of course. The aspect that limits temperature of the discharge air is, how dry is it? If dry and the air temperature is on the low side it may cool the skin by evaporation. Comfort-killer.

    In my example, the air supply came out about 95 to 100 degrees which means either the space has less heat loss than you are used to, or you are moving a lot more air. (With a fixed air temperature, volume is your variable.) Yes, lower water temperatures mean lower air temperatures, all other things being equal.

    As for cycling, I use constant airflow as a principle. Cycling is not in my vocabulary :)

    Less "on-off" perception, better filtration if properly done and smoother temperature control. Modulating valves for HW at the coil and things run very smoothly with constant air circulation.

    With the deeper coils, say 6-row and with good counterflow, you can get leaving air temperatures higher than your leaving return water temperature by a few degrees. (Return water leaves by the incoming air, hotter water gives a nice send-off to the leaving air.)

    Does that help?

  • Mark_46
    Mark_46 Member Posts: 312

    it does help. But I'm sorry to say, my system cycles :o).
    I wanted to get some of the details of that particular system you worked with because I am now focused on balancing and tuning my systems. My goal now is to ring out as much efficiency as possible on top of what I've already achieved by installing new equipment and insulating the house.

    Right now my boiler is running 180 degree water as a default for no other reason than that is how the boiler leaves the manufacturer. But I'm pretty sure I can come down off that point quite a bit and still heat comfortably. Right now as is, the system heats well and at 180 it definitely modulates but I dont think there is much condensing taking place.

    Currently, I have no way of controlling GPM so I believe boiler water temp and CFM will be the main variables available to me in tuning these systems. Particularly, how they work together. By the way, when lowering the boiler set point temp, how does that effect the BTU output/ratings?

    What Im struggling with in order to begin measuring static pressure, velocity and volume, Dwyer claims the Pitot tube in the duct you are traversing for measurement should be located 8.5 or more duct diameters upstream and 5 or more duct diameters downstream of elbows or obstructions. I dont have either available. So, even though Dwyer offers a low cost manometer plus the cost of the Pitot tube, I'm not sure if its worth it.

    But on the other hand, if I can at least get a ball park measurement I can begin to better tune the system. Does that make sense? Is there a cheaper and simpler way to go about it?
  • Brad White_9
    Brad White_9 Member Posts: 2,440

    Let's not hijack NRT Rob's post shall we? :0)

    Write me off line or with another thread if this is getting intense. Sorry Rob!

  • Jed_2
    Jed_2 Member Posts: 781


    Check this link out. It might be useful to you.

  • Cosmo_3
    Cosmo_3 Member Posts: 845


    You might have to navigate through the home page. Just look for "Building HVAC" and right click.

    As always, my favorite engineer wallie Mr. Brad White has some great posts

  • Cosmo_3
    Cosmo_3 Member Posts: 845

    Did you want a ducted fan coil, or a non-ducted fancoil?

    When you said garage I assumed no duck sauce

  • Pat Reardon
    Pat Reardon Member Posts: 1
    Worth a look

    Hi Rob,
    Look at these units http://www.profab.org/Products/HeatHandler.aspx

  • No ducts, and for some reason I still can't find any de-rating info on there.

  • thanks guys!
  • heatboy
    heatboy Member Posts: 1,468
    The Crown Sante Fe..........

    ......... sold by Crown Boilers is a very nice unit. Installing one right now. Very well made and thought out. First Company seems to be the best known, but the quality is not that good on the dozen or so I have seen.


    The Radiant Whisperer

    "The laws of physics will outweigh the laws of ecomomics every time."
  • Bob Knebel
    Bob Knebel Member Posts: 26
    Water Temp Correction Factors for Unit Heaters

    Howdy Rob,

    I don't know if anyone answered your original question about running unit heaters at lower water temps. The following install manual for Beacon Morris heaters gives some correction factors (see page 8) that would probably apply to many brands of hydronic unit heaters and air handlers:


    We've used these corrections many times for lower temp boiler operations. Hope this helps. Have a good one ...... Bob Knebel / Radiant Engineering, Inc.
  • Joe_75
    Joe_75 Member Posts: 57
    heat handlers

    I carry a line of heat handlers. Here is a web site if you need more info call me. 1-406-270-5015

  • Thanks so much for all the help everyone, this got me on the right path for sure.
This discussion has been closed.