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  1. #1
    Join Date
    Feb 2008
    Posts
    20

    Which size Unico to go with?

    Thanks to all who have commented on my previous post about seeking Unico proposals for adding air conditioning. In reviewing 3 proposals, the only remaining issue for me is a discrepancy in the load calculations/recommended size unit by the low cost proposer. Here's the house description:

    Small 2 bedroom slab-on-grade home which has radiant in-floor heat. Upper Midwest, 1 mi. from a Great Lake. Main house is 890 SF: Living/Dining combined and Kitchen face east, Kitchen is on southeast corner; on the west side, the Bedrooms flank one Bath and central Hallway/Attic access. Utility room 130 SF is attached on south, access door from Kitchen is often closed. Garage attached on south side of Utility. Large east windows at Living and Dining and Utility. Seasonal canvas awnings limit solar gain on Living, Dining, and Kitchen. House is clad in stone, together with the concrete slab it tends to provide a stable environment. Attic insulation is original mineral wool plus 3 1/2" batt for total ~6", some additional batts around eaves; exterior walls 3 1/2" batts; windows mostly original single-pane with new wood storms, 3 large windows on east side are Thermopane. I've been using one inadequate small window air conditioner, I usually keep many of the wood storms on in summer to protect the old wood windows; during moderate temperature, ventilation is through screen doors and kitchen screens, that's adequate.

    The lowest cost proposal recommends a 1.5T unit, I asked this contractor to double-check in light of the other two proposers recommended between 2.0T and 2.5T (depending whether the Utility room is served or not). The low proposer says they checked with a second engineer and stand by their 1.5T recommendation regardless of whether future home owners use awnings or not, tree shading is reduced, etc. This contractor states they are Unico certified trained. I am seeking references from them to check out.

    I certainly do not want to pay for more capacity than is necessary, I am leaning towards accepting the 1.5T if their references check out, the fact that this house's environment tends to be stable if rapid temperature swings are avoided (esp. solar gain through windows) is an important reason why I tend to favor their recommendation, plus proximity to lake. Comments, opinions welcomed, thanks.

  2. #2
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,184
    Just remember how much Unico kills capacity. An "024" outdoor unit that would rate around 2 ton with a standard blower is probably 17-18,000 BTU with a Unico. So you have to pay for a larger outdoor unit to get what you need. So if load says 1.5 ton, the outdoor unit better be the 024.

  3. #3
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,104
    As baldie said. You lose some capacity with HV systems compared to the OD units rating.
    We're not there to double check their calcs.
    So 1.5 could be right.

    What ID design temp did they use.
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  4. #4
    Join Date
    Feb 2008
    Posts
    20

    1.5T for 963 SF sufficient?

    Sorry for the delay to reply, I was waiting to receive additional information from the contractor.

    Through email confirmations, the low proposer is very much standing by their recommendation to go with a 1.5T Unico system with a 1.5T Carrier condensing unit. They sent me their "System Sizing Summary" sheet. They state the design is to be able to cool the house to 75* on a 95* day. My very careful interior wall-to-wall floor area measurement now totals 841 SF for the main house (including closets, most of which have louver doors) plus 122 SF for the Utility room, grand total 963 SF of 8' high ceiling areas to be cooled. The proposer's sheet listed "840 SF" for their calculations; when I noted to them that they did not include the Utility room (although their proposal noted it would be served), they replied that the 1.5T is sufficient for the entire 963 SF. They say if the 1.5T does not cool properly I will not have to pay for corrections. Again, this slab-on-grade, stone faced house tends to be very stable, I use seasonal canvas awnings on the east side, two other contractors proposed larger systems (2.0T or 2.5T depending on whether the Utility room is served or not). I called Unico national office and spoke to a very helpful gentleman, however he didn't offer a definite opinion. Because the low proposer is stating in emails that they will stand by their design at no cost to me, I am likely to accept their bid. It would sure help in my decision if a professional member of the forum could offer some opinions. Thanks.

  5. #5
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,104
    As long as you get that in writing.

    Go for it.
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  6. #6
    Join Date
    Apr 2004
    Posts
    420
    Also, did the 2 and 2.5 ton proposers make similar "stand by their numbers" statements, with reasons? Did they provide copies of the system sizing sheet? Better yet, ask them to sit down next to you with their calcs and go over them with you. Doubt they'll leave a copy (we don't) until you're under contract, but we WILL go over them line by line, especially when there is some confusion before a homeowner who might be presented with 3 very different quotes. Unlike other, perhaps more forgiving, conventional systems, Unico is the greatest waste of your money IF over-sized, shooting their larger latent capacity to pieces (IMHO, one of their greatest assets). Not saying which bid is correct, but you'll need some substantial proof of due diligence paid before committing I'm sure. Since the lower capacity proposer provided this, perhaps the choice is clear unless the others step to the plate too.

  7. #7
    Join Date
    Dec 2006
    Location
    Middle Tennessee
    Posts
    11,347

    *

    Quote Originally Posted by 1634j View Post
    They state the design is to be able to cool the house to 75* on a 95* day.
    --

    hey, i dont know about you, but when its 95 degrees outside i want it 70 degrees inside!

    and never had a problem getting that temp in my house!

    even in when i lived in Miami FL.



    .

  8. #8
    Join Date
    Jan 2004
    Location
    Lancaster PA
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    68,104
    Quote Originally Posted by Airmechanical View Post
    --

    hey, i dont know about you, but when its 95 degrees outside i want it 70 degrees inside!

    and never had a problem getting that temp in my house!

    even in when i lived in Miami FL.



    .
    Is that when you had the 5 ton system in the 1400 sq ft house.















    Just jerking your chain.
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  9. #9
    Join Date
    Dec 2006
    Location
    Middle Tennessee
    Posts
    11,347

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    Quote Originally Posted by beenthere View Post
    Is that when you had the 5 ton system in the 1400 sq ft house.


    you so crazy:

    first house i ever rented (for 15 years) was 1500 sq. ft. twv036 with a ttn036 cond.

    next house i bought (lived there for 8 years) was 2000 sq.ft. had a tweo48p with a ttno48 cond.

    both of those houses were in Miami FL.

    here in Cookeville TN. i bought a house 2150 sq. ft. it has a 18 seer Am/Stand 4 ton (forgot the m&s#)

    all the houses i have owned would bring the temp below 68 degrees on any given hot day!

    oh, and i never had humidity problems so----------



    .

  10. #10
    Join Date
    Jan 2004
    Location
    Lancaster PA
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    68,104
    Lol
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  11. #11
    Join Date
    Jul 2001
    Location
    Gold Coast of Connecticut
    Posts
    4,586
    My 2 Ton unit in Connecticut does a good job on 1900 SF no shade standard construction.
    Aire Serv of SW Connecticut- Gas heat, dual fuel and central a/c systems installed and serviced

  12. #12
    Join Date
    Dec 2006
    Location
    Middle Tennessee
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    Quote Originally Posted by Freezeking2000 View Post
    My 2 Ton unit in Connecticut does a good job on 1900 SF no shade standard construction.
    now that is undersized



    .

  13. #13
    Join Date
    Jan 2004
    Location
    Lancaster PA
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    68,104
    Alittle oversized for his area.
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