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Duct tweaking

skyking1
skyking1 Member Posts: 62
in A-C, Heat Pumps & Refrigeration

I had an engineer do a Manual J and design based on my routes available. I had put two registers in this room " just because" it seemed proper, not based on anything else.

He came back with a load of only 60 CFM for this common room.

I did send him a question on it but wanted some other inputs.

Will the comfort suffer with only the T-8 register location and delete T-7? It would easily handle the load. The big window is N-NE facing and the little one E-SE, so they don't ever get beaten on by full sun.

This system is primarily AC with floor radiant for heat.

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Comments

  • pecmsg
    pecmsg Member Posts: 6,157

    you don’t do it to the routs available. Something needs changing!

    skyking1
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 17,943

    He's the engineer. If he commonly does this type of work and knows what he is doing it should be ok. 60 cfm seems a bit light to me but it's probably fine. He did the load.

    skyking1
  • bburd
    bburd Member Posts: 1,166
    edited June 6

    If these are ceiling diffusers or high wall registers, I would eliminate T-8 and use a corner blow ceiling or double deflection high wall type at T-7. That would direct the flow of cool air towards the load and minimize drafts felt by the occupants.

    If they are floor registers I would eliminate T-7 and keep T-8.

    8 inch duct is larger than you need for these loads.

    —
    Bburd
    skyking1
  • pecmsg
    pecmsg Member Posts: 6,157
    https://forum.heatinghelp.com/discussion/comment/1857370#Comment_1857370

    exactly why I don’t trust him!

  • JUGHNE
    JUGHNE Member Posts: 11,441

    When I was doing new houses, I would only do the calculations for the heat gain/loss.

    Then use my gut feeling/shoot from the hip/"cowboy" method of duct/supply locations. However, every room other than bath and kitchen did get more than enough return, which I have seen constantly short changed in most houses.

    If this were my house and looking at cooling load only I would put a supply in the corner where T-8 is. Then put wall stack in the inside wall where T-7 is located.

    I am assuming the ductwork is under the floor in the basement.

    Put high wall return on the left inside wall about across the room from the door.

    Run 6" to both supplies and use 2 stud spaces for the high wall return.

    In my opinion this will mix the air up and draw the hotter air from the ceiling.

    This is what I have done in my own house that I have radiant floor heating in.

    I am not an engineer by any means and looking forward to comments for my hack method.

    skyking1
  • skyking1
    skyking1 Member Posts: 62
    https://forum.heatinghelp.com/discussion/comment/1857372#Comment_1857372

    This is the 2nd floor, with vaulted ceilings. Everything is floor registers. I read your comment while we were working on the hydronic extrusions but was not logged in to answer.

    We looked at the volume of the room and just did not feel comfortable with omitting T-7. This discussion helped me get there. I'm also skeptical about the load and will balance the system when we get it going.

    I will need to go through an I-joist and then go back to the wall there to put in T-7. I ran the hole locations through Forteweb, these joists are weyerhaeuser upstairs. I plan on side tapping the 8" with a 6" to do that, Then an 8x6 reducer over to T-8.

    In reality, T-8 is centered on that 4x6 window there, more in the middle of the room. T-7 will be one joist space to the right.

    I designed the home and have a chase coming up for ducts and plumbing and the hydronics.

    Thanks for your help, all who chimed in.

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