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Q abought high velocity HVAC

Reinvent Member Posts: 43
I am the PM on a remodel of an old house that is going to get HVAC heating. One unit will be put in the basement to supply the first floors needs. A second unit will be placed in an attic space to provide the second floors needs. The attic is only over the front half of the house. The back half of the house has a low sloped flat roof.
The problem is that the ceiling in the back half of the house has joist that run perpendicular to the HVAC location. Was thinking maybe the small size of high velocity ducting could be run thru the joists without much damage.
Are there any cons to high velocity ducting? If this seems like a good idea what brands of equipment would you recomend. What brands of heat exchagers do you like.

Thanks in advance.


  • Andy Morgan_2
    Andy Morgan_2 Member Posts: 147

    Even though the ducting is small, you would still need to bore a four inch hole to accomidate the duct with insulation. Also, HV uses many more ducts than conventional AC systems. This adds up to a lot of drilling and making swiss cheese out of your joists which is not good. I would look at putting a soffit or a chase in somewhere to run the main trunck, and then branching in between the joists through the bays to the locations. Good luck with your project.

    Andy Morgan

    R. Morgan Mechanical, LLC
  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928
    Not Exactly Fun...

    ...but it works--at least with Unico as their connectors are the same size. Use central vacuum tube. I insulated with bubble foil and used 2½" holes. Align the holes CAREFULLY to include running a taught string to ensure that you account for any sags/flaws in the framing. If more than ¼" or so difference from the bottom of the joists make correction by measuring distance of the string from the joist.

    Found that a good boring bit works well and very rapidly, but particularly if the wood is old, dry and hard work with two people; stop as soon as the pilot screw emerges from the back and finish the hole from the other side of the joist. If you don't, you risk "blasting out" very large chunks of the joist. Hole saws are much better in this regard, but slow and utterly exhausting in such a position.

    Still though verify that the joists are of sufficient size to allow 2½" holes.

    Unless you're lucky and have an end where you can insert long pieces, cut tube lengths at the actual joist spacing (not the distance between) and pre-insulate, leaving about ¾" uninsulated at each end. Cut pieces very accurately and again use two people to wrap and tape. Glue in the couplings and wrap "patches" around the uninsulated area. We had no problem angling 16" pieces into 14½" cavities.

    p.s. These are 2x10 joists only 4' long so the "Swiss cheese" won't affect strength.
  • Sweet_2
    Sweet_2 Member Posts: 143
    Mike T.

    Were looking at getting training to install these systems. Curiuos if these systems create more noise via return air or supply. Thanks
  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928

    This is the first HV system I've installed--and it's not yet complete. Have though felt/heard a number in this area. Noise is subjective of course but to my ear they are as quiet or quieter than well-done traditional systems.

    Note that if you install in the manner above that you must still install at least 3' of the sound-attenuating tube at the end of each branch.
  • clammy
    clammy Member Posts: 3,092
    why 2 units

    TRhe beauty of these systems is you can run the the branch runs with out to much loose i,ve done three story homes with one unit from the attic as for a basement unit with floor registers i 've always found it hard to find low traffic no furniture spots to install them .Over the years i,ve worked on and install a few of thr unico systems as mike says use there full attuner on all runs instead of the suggested minuim amd sound abd balancing is never i issue .Try lining your return air box and use a good ra grill instead of a cheap stamp grill also 1 sq. ft for each 1 ton of ac that always keep your returns quite and makes your systems difference to everybodies else by not having a noisey return also i usually will install on a 2 story home 1 central hall return and install returns in all second floor bedrooms makes central return smaller and give a closer over all room to room temp with in 2 degrees when i install them this way .Remenber to size your returns for a lower static pressure .It's mostly all common sense stuff as with every thing in life peace and good luck clammy
    R.A. Calmbacher L.L.C. HVAC
    NJ Master HVAC Lic.
    Mahwah, NJ
    Specializing in steam and hydronic heating
  • jerry scharf_2
    jerry scharf_2 Member Posts: 414
    check out the lennox 1 tooth hole saws


    They cut a bit rougher than a standard hole saw, cut as fast or faster than a self feeding bit and are the easiest clearing hole saw ever.

    The big up side is that they deal with nails better than anything I've ever used. If you lighten up a little on the push when you hit a nail, it cuts right though it with little damage to the bit. Since it's one big tooth, there's a bunch of carbide there and sharpening is a quick pass with a diamond dust file.

    The down side is that they can only cut with about 2" deep, so I have to spend some time with a hammer and chisel on 4x posts.

    I love the ones I own, and I love lending them. I know the people will envy me when they are done, and they really can't trash them the way you can other borers with nails.

  • Dave Bush
    Dave Bush Member Posts: 155
    1 tooth hole saws

    I laughed at these when I first saw them.

    I ain't laughin' anymore! They're awesome holemaking devices.
  • Dave Bush
    Dave Bush Member Posts: 155
    They're a means to an end.

    They're not ideal, but when designed properly, and installed exactly to the manufacturers requirements, they can provide decent, low noise comfort cooling.

    Conventional AC is my preference every time. Often, however, the demolition involved drives the cost too high, or renders it vedrboten. Often, a homeowner will forgo central ac after seeing the cost of installing it, then repairing their home.

    This is where the HV HVAC units come in.

    The Unicos and Spacepaks are not necessarily EASIER to install, they are, in fact, more difficult to install properly. This is because of the typical mfg hype over ease of installation.

    Whatever you do, of you've never done one, get ahold of a knowledgeable rep, and buy some of those 1 tooth holesaws.
  • John Mills_5
    John Mills_5 Member Posts: 950

    Check the ARI ratings on your chosen equipment. The high velocity stuff reduces SEER & capacity. A 12 SEER 3 ton outdoor unit may end up near 10 SEER and 30,000 BTU so choose your outdoor unit accordingly.
  • Dave Bush
    Dave Bush Member Posts: 155
    Excellent point

    Oh hairless one.:=}
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