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Thanks for good ideas here. I chuckle every time see Swampeast. THERE is a place that's got to need air conditioning.

Would someone comment on this thought: It is colder here in Minneapolis in winter. The idea of having carefully plugged and insulated the attic to R38, but then having 10 or so Unico [or Spacepak, etc.] hollow R8 pipes of cold air through to the lower floor makes little sense.
How about working 2 inch diameter blastgates [ for woodworking sawdust vacuums systems ] XTmodRRvinto the ductwork at ceiling of 2d floor. Any downside? Heck a guy with too much money could run the electric ones and open them seasonally with one switch.


  • Joe_75
    Joe_75 Member Posts: 57

    What does everyone think about the Unico system. Any good or bad experiences.
  • Brad White
    Brad White Member Posts: 2,393

    Hi Joe-

    Great to hear from you again. Here is a reply I gave to ME on a similar question.

    The thread URL is this:

    Sensible cooling and fast cool-down are not the strong-suits of this kind of system. They want to run long and low. (Same tonnage, about half the air as you know). Hence, turn-over takes a while. Not effective for quick pull-down after a weekend away or supportive of setbacks. IOW, your controls should anticipate this and start the cooldown earlier. Not sure if "Smart Response" works in a cooling system as it does for heating.

    High delta-T means low dewpoint on the air. Great here in New England where humidity control is key. High desert of eastern Colorado? I always liked blow-through, these are draw-through usually. Not sure if over-drying is of concern in summer.

    For ease of balancing, I prefer to "loop" the duct if I can. Ring ducts make for very even pressure all around.

    When you go to the outlets especially near the fan but short money if you do it everywhere, use the attenuator kits for the outlet branches. Use the length of the runouts to your advantage for sound attenuation. If they offer as part of the system a fan outlet attenuator, get it or leave room for one later such as a drop-out section with band clamps. Generally they are surprisingly quiet but sometimes you just have to reach for the stars. Long straight shot out of the fan, no hard turns within the recommended diameters. Use wyes instead of bullheads, make it easy on the air. The duct is all 7 inch maybe 9 inch round anyway. Small stuff.

    For fittings in a pinch I have used Lindab fittings with the dual gaskets and nice long radii on the elbows, very smooth. But mostly the fittings and duct are proprietary. No matter what though, seal the living s--- out of the ductwork if not a self-sealing system. Brush on mastic. A leak at that velocity can vissle!

    Heating is fairly well suited given the air volumes (lower with warm air than for cooling in general). If using a hot water coil can work well using good common sense practices. Not sure how flexible the coil selections are for low-temp condensing boilers though. Heck, you are probably going radiant anyway so why did I bring that up? :)

    Refrigerant- common sense practices of course. Lift and pressure are different given lower SST's on the coil. Charging them can be particular I am told.

    Use the usual good things such as auxilliary drain pans, water trip switches, zone for like exposures, stuff you know to do anyway.

    Fancier outlets are available in several metals, woods and -egads- platics.

    There are dampers available that are inserted in the nozzles with long wires. If your client is an Endoscopist, perhaps he/she can relate!

    Overall- great in retro construction because of space concerns or wherever you have constraints. Sheetmetal costs are less of course. Still -given a choice I would use conventional cooling if space was not an issue. The low turnover rate does not allow filtration effectiveness as does a conventional system.

    As stated though, for dehumidification it is hard to beat 40 degree supply air. See if that works with you or against you.

    My $0.02,

    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"

    -Ernie White, my Dad
  • mtfallsmikey
    mtfallsmikey Member Posts: 765
    Brad, can you explain

    Some basic ring ducting theory? Ran into this when a new office building was built on the former employer's site. I don't really grasp the concept myself.
  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928

    Not Brad but "ring ducting" is nothing more than turning the supply plenum into a loop. Simplest way to visualize is a circle with a leg leading to the air supply. The individual branches (to outlets) are all connected to the circle. Such is called a "loop system" in Unico literature and is the preferred method if at all possible.

    The advantage of the loop is that it guarantees equal pressure at the connection point of ALL individual branches. If all of these individual branches are essentially identical (length, layout, terminator, etc.) then the output from each branch will also be almost identical.

    If you haven't used a high-velocity air system before, I HIGHLY suggest downloading EVERY BIT of engineering information from the Unico website. You have to look a bit to find it, but it's genuinely exceptional--study well and you have everything (save actual load sizing) to design a wonderful high-velocity system.

    There are many rules to follow with ANY main layout--the loop system however has the fewest rules and is by far the easiest to engineer since you don't have to consider the effect of the main on the branches.
  • Dave_4
    Dave_4 Member Posts: 1,405
    ring duct with 2 stories?

    1. If the unit is in attic of a two story house,
    the various mini-duct runs will naturally not be of even length.
    Is the loop [ring] plenum, which makes for an evenly pressurized plenum, nonetheless useful/preferrable?
    It seems to me the benefit may be diminished.

    2.If one of your 2nd floor ceiling outlets is right there a foot or two below the plenum, do you just snake the mini duct around the attic floor to get the length for sound attenuation?
  • Joe_75
    Joe_75 Member Posts: 57

    Brad Mike thanks for the replies. I am hiring an AC/forced air guy so I have been looking into this line of work. The guy is good so now I can do some of the AC work that I have passed along on my jobs.
  • Troy_3
    Troy_3 Member Posts: 479

    Yes a short drop should be bent around to add run length. The key here is a bend in the run. Also the return wants a bend. It helps to absorb sound and not trumpet sound. I spec. Unico on all my radiant jobs that want a/c. I think they work great. Even works very nicely with low temp. water for spring/fall air heat. You may need to plug outlets in the winter when duct is in unconditioned attic. The warm moist air tends to condense and run back out.
  • A.J.
    A.J. Member Posts: 257
    you haven't seen nothing yet

    Just heard that there is a variable speed unit coming to market
  • Rick_65
    Rick_65 Member Posts: 4

    Hi-Velocity Systems has the variable speed out now.
  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928

    If serving two floors from the attic, you should almost certainly use a loop system!

    Again, the looped supply plenum ensures that pressure is equal at the point of connection for all branches. Longer branches do mean more restriction and thus less flow, but at least there are FAR fewer rules for the placement of branch takeoffs than with any other form of plenum layout.

    A "standard" branch has 10' of sound-attenuating tubing. Shorter branches really shouldn't be used as there may be noise problems. Unico now has a special outlet that connects directly to a plenum, but I have not used. There are also perforated restrictors in specific percentage values that can be used to make a "standard" 10' run "act" like it's longer.

    Unico provides simple instructions for figuring the "equivalence" of a run longer than 10'. In essence, a standard run has a value of 1.0. Longer runs have an equivalent value less than 1.0. You use the equivalent values when totalling to ensure that you have a sufficient number of outlets for the system as a whole.

    As long as you have decent access a loop system with the plenum in the attic is likely the only practical way to serve a two-floor home with a single system. Granted the runs to the ground floor will be longer and have less than 1.0 equivalent value, but heat gain on the ground floor is almost always significantly lower than the floor above.

    If the plenum were in the basement however, it would be extremely difficult to serve two floors as you would probably need a ridiculous number of branches in the upper floor where they're probably most difficult to run.

    One often simple way to work with the 10' minimum length for branches is a simple criss-cross. Say an upper floor room needs two outlets. Space the takeoffs about 8' apart and run the branch lines close to the takeoff point of the opposite branch.

This discussion has been closed.


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