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  1. #1
    Join Date
    Sep 2009
    Location
    barrie,ontario
    Posts
    51

    hydronic coil question

    ive got a small job for my brother inlaw to do.he has a wood fired boiler he uses to heat the basement floor and we want to add a coil to the existing oil furnace.i managed to salvage a decent used coil from a tear out at work so we gonna save some coin.my question is can this coil be added to the return air side of the highboy oil furnace?the job would be super simple if it could.i asked this same question at our wholesalers today and their tech guy told me not to.his reasoning was that the higher return air temperature would not allow the blower motor to run cool,the added heat would be the death of the motor.we already have a large A-coil in the plenum for cooling so i would have to transition off the PTO in a rather tight spot.if the water coil cant go in the R/A.

    cheers
    if it wont go,get a bigger hammer.

  2. #2
    Join Date
    Sep 2009
    Location
    barrie,ontario
    Posts
    51
    please!
    if it wont go,get a bigger hammer.

  3. #3
    Join Date
    Jun 2013
    Location
    Cleveland Ohio
    Posts
    30
    Not knowing what the performance of the hydronic coil is , what the supply air temps will be , what the existing motors rated operating temps are , etc.... My SWAG tells me if its a PSC motor you'll most likely be ok , if it's an ECM motor I know they are not fond of heat , they are trying to dissipate heat so showering them with heat is typically a bad idea . imho

  4. #4
    Join Date
    Jan 2010
    Posts
    5,812
    Is the top of your plenum a L or T ?

  5. #5
    Join Date
    Sep 2009
    Location
    barrie,ontario
    Posts
    51
    blower motor is just a plain jane one.oil furnace is a tall boy with 1 PTO connected to a branch.ive got tons of room to transition the coil into the return air boot and drop.

    thanks
    if it wont go,get a bigger hammer.

  6. #6
    Join Date
    Aug 2001
    Location
    Pavilion, NY
    Posts
    2,015
    I don't think the motor will care. My only concern is passing 100?? Degree air through your oil furnace may not transfer as much heat and you will probably cycle on limit. If it is an old school fan/limit you may need to adjust the settings
    ...

  7. #7
    Join Date
    Sep 2009
    Location
    barrie,ontario
    Posts
    51
    my cheap azz bro-inlaw rarely uses the oil furnace.basically it will only act as an air handler.
    if it wont go,get a bigger hammer.

  8. #8
    Join Date
    Jul 2000
    Location
    Northern Wisconsin
    Posts
    1,934
    Before you start I would suggest measuring the ESP on the oil furnace as is. Too much heat across the blower motor won't mean a thing if the static pressure increase from adding the extra coil exceeds the capabilities of the motor not to mention that if the static gets too high the air conditioner could also have serious issues.

    If the coil you got is an off the shelf unit you should be able to come up with it's specs that will show how much SP it will add at the CFM's you'll be trying to put through it.
    Use the biggest hammer you like, pounding a square peg into a round hole does not equal a proper fit.

  9. #9
    Join Date
    Sep 2009
    Location
    barrie,ontario
    Posts
    51
    thanks FC,unfortunately i have no specs on the coil.i salvaged it from a tear out.i think im just gonna go for it,can build all the transactions at work real cheap.blower motors are cheap as well.gonna be a nice little side project with a learning curve since we almost never install hydronic coils at work.

    cheers
    if it wont go,get a bigger hammer.

  10. #10
    Join Date
    Aug 2012
    Location
    NE wisconsin
    Posts
    392
    I have seen it done, and the only problem they had was the thermal fan switch would not let the fan shut off. We had to use a relay to switch control from the oil furnace when the boiler was hot.

  11. #11
    Join Date
    Jan 2007
    Location
    Stongsville Oh
    Posts
    872
    I would add a bypass with damper just in case. You could do a little balancing act when it is completed if you need to increase airflow or decrease temp.
    ckartson
    I didn't write the book I just read it!

  12. #12
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    66,755
    Check the rating on the blower motor. See if it is rated to work in ambient temps above 120F. If not, it will over heat and shut down.
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  13. #13
    Join Date
    Sep 2009
    Location
    barrie,ontario
    Posts
    51
    bingo,there we go.thanks to all for their input.

    Quote Originally Posted by beenthere View Post
    Check the rating on the blower motor. See if it is rated to work in ambient temps above 120F. If not, it will over heat and shut down.
    if it wont go,get a bigger hammer.

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