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  1. #1
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    Oct 2019
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    Iowa
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    Ceiling supplies for basement finish. Low CFM for larger rooms

    I am finishing my basement here in Iowa. The hvac duct work I need done is the only part of rough I am not doing myself. Zoning would be nice but not in the budget. I am having the same gentleman do my basement HVAC changes that did the work when I built the house. He is semi retired now but still does all my service and has became a friend over the years. He does excellent work but is very much a 'rule of thumb' guy so I am looking for second opinions.

    To get our energy credits, the local utility company did an updated manual J on the house with my updated basement plans and I have CFM numbers for the new rooms. Heating will be the main load, cooling is significantly less. Since we are spray foaming the basement, the ceilings are already insulated, and only have two egress windows the CFM needs for the various rooms are pretty low with only 283 cfm for whole basement. The family room is the highest at about 80 cfm, the two bedrooms are around 50, and the rest are all under 20. The ducts will be a mix of 6", 5" and 4". All supplies will get dampers and we will balance all the rooms with a hood. There will be a large central return and smaller returns in the bedrooms and jump vents for the storage areas which have supplies.

    I will be using all Hart & Cooley 682's and 612s registers as I did when we built the house. I will have all ceiling supplies and am somewhat limited for locations for the ducts because of plumbing, and the ductwork for the rest of the house. For at least the family room and the bedrooms I am limited to having the ducts somewhat in the center of the room running parallel to the long walls of the rooms.

    In looking at the engineering data for the H&C grills it seems in a number of the rooms, I am not going to have enough CFM needs to get good throw for the size of the room. So for example, one 13x20' bedroom needs 52 CFM. A H&C 682 4x10 2-way will deliver this at a face velocity of 500 FPM so noise should be good. However the throw is only 5 feet. So even with the register in the middle of the ceiling depending on how we orient it, it will barely reach the long walls and be a good 5 feet short for the short walls, though the Coanda effect should give some additional distance.

    So any suggestions on how to best maximize heating comfort in these larger rooms with smaller CFM requirements? For example, should I go with smaller 2 or 4 way grills in the rooms resulting in longer throw but higher noise. In 13x20 room with one long wall being the exterior would you align the register's throw to the long walls or the short. I know the normal recommendation would be to blow towards the external wall.

    Sorry for being long winded but I wanted to give all the details. Thanks for any suggestions. I appreciate it very much!

  2. #2
    Join Date
    Jan 2004
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    Will the room have its own return or will it use an under cut door?
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  3. #3
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    Oct 2019
    Location
    Iowa
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    Thread Starter
    All the rooms will have a return except for the bathroom and two storage rooms. The storage rooms will get jump vents/ducts. Doors will be undercut but I am not relying on that.

    Thanks!

  4. #4
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    Jan 2004
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    Might need to switch to a smaller register to get better throw.
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  5. #5
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    Oct 2019
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    Iowa
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    Thread Starter
    beenThere,

    Thanks for the reply. I appreciate it. I will check and see what my guy's supply house has available for smaller supply registers. If we need to we can always order online.

    With smaller registers that may still be throw challenged due to low supply CFM what is the best compromise for directing the airflow? 1 or two way blowing towards the long walls (shortest throw distance) or blowing towards the short walls (longest throw distance) ? Or go with a a 4 way and hope for good mixing in the room? Or as 54RegCab here suggests, blowing straight down.

    Thanks again for any suggestions!

  6. #6
    Join Date
    Aug 2002
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    If the walls of the basement are about 50% below grade and the floor is below grade, it is doubtful you will need any cooling in the summer. You may need a dehumidifier down there in the summer though.

    Ceiling supply’s in a below ground basement always seem to leave the rooms cold near the floor. I like to run the supplies down the outside basement wall of each room so it discharges near the floor, seems to help tremodously in below ground basements.

    Another thing that will help is if the floor in the basement is slightly elevated or dry-core floor sheets are used as a subfloor before the carpet or wood flooring goes down.

  7. #7
    Join Date
    Aug 2009
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    Beatrice, NE
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    If you can get the registers near the outside wall rather than the middle take a look at the HC 661 or put in a 2x10 or 12 white 421 floor register, punch holes in the ends and mount it with white screws.

  8. #8
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    Oct 2019
    Location
    Iowa
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    Thread Starter
    AdvancedResponse,

    Thanks. You are correct, the basement cooling load (114 cfm) is lower than the heating load (300) . Unfortunately with spray foam in the 2x4 exterior walls there won't be room to fit supplies in the walls.

  9. #9
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    Oct 2019
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    Iowa
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    Thread Starter
    Quote Originally Posted by BNME8EZ View Post
    If you can get the registers near the outside wall rather than the middle take a look at the HC 661 or put in a 2x10 or 12 white 421 floor register, punch holes in the ends and mount it with white screws.
    BNME8EZ

    Unfortunately, there is no way to get closer than 4' to any of the exterior walls due to all of the supply ducts in the joist bays serving the upstairs exterior walls so the middle of the room for the family room and one bedroom will have to do. The other bedroom supply will be on the opposite wall from the exterior due to joist direction and the branch for that end of the house.

    I had not looked at the HC 661. That does have more throw than some of the others like the 682, I assume because of the narrower vane spacing. Thanks for the recommendations. I appreciate it.

  10. #10
    Join Date
    Aug 2002
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    My next suggestion would be:

    Can you get them low on an interior wall near the floor blowing towards the outside wall? And locate the returns in the ceiling near the outside walls?

    I just find having the heat supply’s near the floor more effective for heating a basement as the floor tends to be cold and with low volume ceiling registers the heat just stays at the top of the ceiling.

    Is your flooring(carpet/tile/carpet) going directly on the concrete floor? I would recommend a dry-core sub floor or similar to have a warmer feeling floor.

  11. #11
    Join Date
    Jan 2004
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    If the register is in the middle of the ceiling then a one way throw would give good air mix.
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  12. #12
    Join Date
    Nov 2004
    Location
    SW FL
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    ANY room with < ~0.33 CFM / square foot is likely
    to have an inherent mixing issue / air distribution concern.

    13' * 20 ' = 260 sq. ft.
    ... needs ~ 80 CFM to address mixing issue.

    These situations Obviously need [ slightly ] more air
    IN ADDITION TO smaller diffuser.

    H&C A611 // 8" x 4" // Throw = 10 feet

    _________ 8" X 4" is typical for a small-medium bath room
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    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

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