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High Velocity A/C

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  • High Velocity A/C

    I live in a 2300 sqft cape cod with knee walls in the front and the back of the upstairs and enough attic space. The different contractors I got to look at it said it is not too big of an install and would not be too much of a problem. One was telling me a 3 ton system would be enough for the house, another one said probably 4-5 tons (shouldn't there be a formula so that they all get the same outcome??).

    I got a quote for a space pak system for a bit less than 18k. Still waiting for the other contractors to give me their quotes. I am looking at spacepak and unico.

    I do know that unico is a "modified spacepak", apparently done by engineers that originally worked for spacepak.

    I have a few questions:

    1. I do know that those systems are expensive, but is 18k a ballpark number I do have to estimate or is their quote just plain too high/low?
    2. Is there any difference between Unico and SpacePak that should make me prefer one over the other?
    3. What do you guys think about the high velocity system in general? Does it even make sense?
    4. One of the contractors said I might be able to do conventional systems, one in the basement for the first floor and one in the attic for the second floor. Would you estimate that this comes in cheaper than the high velocity one? Would that even make sense at all?
    5. Do you think there are any alternatives to that? I am not sure if I would want those Mitsubishi things on the walls...
    6. Do you know about the operating costs of a system like that (comparable to regular AC or higher/lower)?
    7. Any idea if I would ever get the money back when I am selling the house or is there no way that this increases the house value by so much?

    I know those are a lot of questions, but I would appreciate the answer on at least a few of them Thank you!

  • #2
    Re: High Velocity A/C

    To answer your first question...Yes. There is a formula. It is called Manual J. One question you may ask your contractors is if they used it?

    An average rule of thumb is 1 ton per 500 square foot. That number is +/-depending on location and insulation/exposure. So by the numbers given and no information of heat gain or loss, I would say that the 4-5 ton is more likely.

    Without knowing the full layout of the house? Any advice to actual size is still a wet finger in the air. The averages do usually hold true unless you have a seriously insulated home. Say if you have 2# spray foam insulation in the walls at 6" giving you an R-48 value or a straw bail house that has a natural R-50.

    Mini-split packages tend to end at 3 tons.
    Last edited by Kevin Jones; 07-15-2010, 09:21 PM. Reason: spelling


    • #3
      Re: High Velocity A/C

      Thank you for your quick answer, Kevin!
      Hmmm... it definitely is not a seriously insulated house. It was built in the 50s and I just started to upgrade the insulation. We are talking about R30 in the attic so far. So based on that, I would say I can go with the 1 ton per 500 sqft and would wind up with about 5 tons - especially, since I told them that I am planning an addition on top of the garage to put a master bath and closet in - still living space and should be counted somewhat.

      So, I'll see what the contractor will say to that and why he is coming in with less tonnage than the others and if he used the formula.

      If anyone has any idea on the other questions - it would be great!

      I am definitely going to give you all then an update on what happened with everything and how it turned out once I pick one and we go ahead.


      • #4
        Re: High Velocity A/C


        I am one of the owners of Unico Inc and would like to put you in touch with my represetative for your area so that they can give you a very good idea as to the requirements for your residence. Please send your contact information to and I will make sure you are contacted right away.
        thank you for your interest in our system.

        Shannon Intagliata


        • #5
          Re: High Velocity A/C

          Thank you Shannon. Just sent you an email.