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  1. #1

    Hmm New AC sizing help, brand, maybe entire system?

    Hello,
    I have a 1486 sq ft ranch on a finished basement north of Detroit, a dual stage, dual speed American Standard Furnace, 11 yrs old (80%) which is 80000 BTU. I also have a 1989 Lennox central AC air conditioner that is finally dying, this last hot summer killed it, sorry I do not have the model in front of me but I do know it starts with 18-31 which I am told is a 30000 BTU unit (2.5 ton)?. Hi efficiency windows in last 10 years, standard insulation in walls and ceiling, and house wrap when re-sided 2 years ago. Up to this summer, the AC was able to keep up, but struggled at times in 95 heat, in the end, she would just start freezing up, compressor almost dead quiet, when it was working you could hear it 3 houses away.

    I was going to just replace the AC due to the fact the furnace has some years left in her and it works great, but after looking at some of the new furnaces and available rebates and talking to 3 companies, I am considering upgrading the Furnace to a 95% efficiency model and a 15 or 16 SEER AC system. I do have 1 more company coming out that installs just about every make under the sun and they are a very reputable company as well. Interested in what they have to suggest, that is next week. Want to get this done before the winter sets in, especially if a new furnace is in the picture.

    My dilemma is: The Lennox contractor calculated that I need 2.4 tons + 10% so he recommends going to a 3 ton unit, The Sears guy, selling Kenmore name as well as Carrier, states to go with a 2 ton AC. I had an independent contractor out last night, has a very good reputation in the area, selling Goodman, said that a 2 ton 16 SEER with a 3 ton A coil would be the correct size for AC system. In talking further, he told me about the matching furnaces as well and how they play together on the higher end units for most of the major brands which sounds like a good idea as far as environment control. This furnace discussion was prompted by me looking at the two stage AC units. Looking at the Goodman DDSXC16 AC and possible the GMVC95 furnace

    So, a couple of questions from you folks in the know: What size AC system sounds appropriate for the house described at 15 or 16 SEER? Is Goodman reliable for both AC and furnace if installed correctly? I do not see a lot of negative feedback on Goodman equipment like I do the others. I am pretty much already done thinking about Sears just due to the bad publicity concerning the way they handle there service. I was actuall looking at Goodman, Amana, and possibly Carrier units as my top picks.

    Thanks, Mike

  2. #2
    Join Date
    Jan 2004
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    Lancaster PA
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    Well if the 2.5 ton you already have is cooling the house ok, going to a 3 ton would probably give you some humidity problems.
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  3. #3
    Join Date
    Jan 2009
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    Keokuk, IA
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    That size home is SE Michigans mild climate probably only needs a 2 ton depending on windows, air leaks and shading I definitely would NOT go larger. Design temperature is 88-89F for that area. Compare that to parts of Texas that are 100F, and a system in Michigan will be 1/2 the size of one in Texas after you factor in humidity. It's very easy to oversize in that climate.

    I like hte 2nd contractor better, but I wonder if he's using a proper load calculation of at least understand how oversizing is bad. I would not oversize the coil to 3 tons. Better to stay no larger than 2.5 Tons, especially is 2 stage. Never oversize more than 1/2 ton on 2 stage equipment, otherwise in 1st stage, you will have trouble removing any moisture.

    Beign a little undersized even, isn;t a bad thing. At worst it falls behind a few degrees in really hot weather, but will catch up overnight, still keep humidity low and will save you money with very long runs times and lower humidity will allow you to keep it comfortable at a higher tmepratures.

    My parents live in Michigan. They system is 2.5Tons in a condo that probably only needs around 1.5 Tons. evne in hotter weather, 71F in there home feels the same as 75F in my home. That's a big difference in energy use.

  4. #4
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
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    34,428
    Your budget. High SEER equipment is likely a lousy investment if you care about ROI. 13/14 SEER is often the wisest move in a northern climate. I'd be hard pressed to take out a Trane XL80 at 11 years. It's just getting broken in. Needless to say I like that furnace!. You could take the thousands you spend on a new furnace and tighten the house, replace lousy doors, blow the attic to R38 or above and pay back so much faster than the furnace upgrade. Same with the premium for 15/16 SEER.

    This year was super hot, don't go bigger just because a 2.5 ton struggled over this summer. Freezing up says low refrigerant or dirty indoor coil, that would explain the problem cooling.

    My cousin built a new house in suburban Detroit. I pointed out that the 16 SEER the dealer proposed would be at its life end when the premium for it was met by the energy savings over a 14 SEER. That's all he needed to hear. Most pros on here will push the most expensive system on the market. I think they are imagining the commission they would get from a sale like that

  5. #5
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,367
    Quote Originally Posted by MikefromMI View Post
    Hello,
    I have a 1486 sq ft ranch on a finished basement north of Detroit, a dual stage, dual speed American Standard Furnace, 11 yrs old (80%) which is 80000 BTU.

    I also have a 1989 Lennox central AC air conditioner that is finally dying, this last hot summer killed it, sorry I do not have the model in front of me but I do know it starts with 18-31 which I am told is a 30000 BTU unit (2.5 ton)?.

    Hi efficiency windows in last 10 years, standard insulation in walls and ceiling, and house wrap when re-sided 2 years ago.

    Up to this summer, the AC was able to keep up, but struggled at times in 95 heat, in the end, she would just start freezing up, compressor almost dead quiet, when it was working you could hear it 3 houses away.

    I was going to just replace the AC due to the fact the furnace has some years left in her and it works great, but after looking at some of the new furnaces and available rebates and talking to 3 companies, I am considering upgrading the Furnace to a 95% efficiency model and a 15 or 16 SEER AC system.

    Want to get this done before the winter sets in, especially if a new furnace is in the picture.

    My dilemma is: The Lennox contractor calculated that I need 2.4 tons + 10% so he recommends going to a 3 ton unit, The Sears guy, selling Kenmore name as well as Carrier, states to go with a 2 ton AC. I had an independent contractor out last night, has a very good reputation in the area, selling Goodman, said that a 2 ton 16 SEER with a 3 ton A coil would be the correct size for AC system. In talking further, he told me about the matching furnaces as well and how they play together on the higher end units for most of the major brands which sounds like a good idea as far as environment control. This furnace discussion was prompted by me looking at the two stage AC units.

    So, a couple of questions from you folks in the know: What size AC system sounds appropriate for the house described at 15 or 16 SEER?

    Thanks, Mike
    2 ton is typical for 1,500 sq. feet, but fresh air and a dehumidifier is required in the basement.
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  6. #6
    Join Date
    Jun 2005
    Location
    SW Wisconsin
    Posts
    5,021
    Hi efficiency windows in last 10 years, standard insulation in walls and ceiling, and house wrap when re-sided 2 years ago. Up to this summer, the AC was able to keep up, ...
    There are many factors that would have lowered your 2.5-Ton system; systems only average 65% of delivered Btuh performance, so there is gain to be had there providing the duct system & other factors are properly tended to...

    As a general viewpoint in your climate you should be able to make a 2-Ton do the job but I would go with a 14-SEER to get the Scroll compressor & a TXV refrigerant metering device which helps on milder days with getting the humidity down.

    I'd never go to a higher SEER than you need to get the components that improve performance; the additional cost of a higher SEER 2-stage is not cost-effective in a northern shorter cooling season.

    In the northern climates it can take considerably more airflow for heating than cooling therefore, the indoor coil needs to be sized to effectively handle that higher flow rate.

    Regarding the sizing of the evaporator coil; a 2-Ton allows for 900-CFM max airflow, so if heating needs more then that which it will with even 60,000-Btuh furnace; I'd go to at least a 2.5-Ton coil or, whatever size works for the required heating airflow, which is usually a 60 to 65-Temp-rise max.

    If they go with an 80,000 furnace it may take a 3-Ton evaporator coil to flow around 1200-CFM of airflow without excessive pressure drop.

    All the important factors need to be considered to get efficient performance in both the heating & cooling modes.

  7. #7
    Join Date
    Dec 2010
    Location
    The Quad-Cities area (midwest).
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    2,743
    Quote Originally Posted by BaldLoonie View Post
    Your budget. High SEER equipment is likely a lousy investment if you care about ROI. 13/14 SEER is often the wisest move in a northern climate. I'd be hard pressed to take out a Trane XL80 at 11 years. It's just getting broken in. Needless to say I like that furnace!. You could take the thousands you spend on a new furnace and tighten the house, replace lousy doors, blow the attic to R38 or above and pay back so much faster than the furnace upgrade. Same with the premium for 15/16 SEER.

    This year was super hot, don't go bigger just because a 2.5 ton struggled over this summer. Freezing up says low refrigerant or dirty indoor coil, that would explain the problem cooling.

    My cousin built a new house in suburban Detroit. I pointed out that the 16 SEER the dealer proposed would be at its life end when the premium for it was met by the energy savings over a 14 SEER. That's all he needed to hear. Most pros on here will push the most expensive system on the market. I think they are imagining the commission they would get from a sale like that
    I agree with B.L., but I'm a little tight with my money. The 80% furnace is fine, so I would just add a 13 SEER A/C unit. In northern Michigan I can't imagine needing "higher" efficiency. Goodman has a scroll compressor in their 2 ton, but you need to ask for a TXV. Also ask for a 24/30 coil (not the 18/24), so it addresses UDarrell's concerns.

  8. #8
    Thanks for all the responses folks. They lead into 2 further questions.

    I have to agree that since I have the AS XL80 dual stage two speed that is 11 years old, and it is running great that I think I will just replace the AC system. Now the questions.

    Since the 16 SEER has a rebate from the local utilities company which makes it the same price as a 13 SEER, is there any disadvantage of going with the 16 SEER (Goodman SSX 16) over the 13 SEER unit?

    Second, the proposal states that for the 13 SEER unit he would go with a 3 ton unit, and the 16 SEER unit a 2 ton unit. Two separate companies came up with this scenario, not sure why. If a unit is rated for 2 tons than why does it matter which SEER value it has? It is my thought that a s ton 13SEER still has the same cooling capacity as a 16 SEER, maybe I am wrong. The 3rd contractor who is offering Goodman products states this is because of the efficiency of cooling is better on the higher SEER units.

    Thanks folks in advance.

  9. #9
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
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    Since the 16 SEER has a rebate from the local utilities company which makes it the same price as a 13 SEER, is there any disadvantage of going with the 16 SEER (Goodman SSX 16) over the 13 SEER unit?
    Yes, see next quote!

    I think I will just replace the AC system.
    To get 16 SEER and a rebate, you need a matching Goodman furnace with high efficiency motor. If you just buy the A/C and coil and put it on the XL80, you'll end up with 14-15 SEER and no rebate.

    Yes, cooling capacity is the same regardless of SEER. You just pay a smidge less to run the higher SEER. Why the 2 sizes makes NO sense!

  10. #10
    Join Date
    May 2008
    Location
    Missouri
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    3,597
    Bald is correct. You'll have to change the furnace to get an AHRI rating to insure you'll get your rebate on 16 SEER. You can't get that rating using your existing furnace! The electric company will want the actual installed rating to qualify you. I'm not a huge fan of multi-stage units, as have a bad past experience with compressor and control problems with some brands. Multi-stage means more controls!

  11. #11
    OK, had my last quote in today, based on the offerings and pricing, they are slightly less than the Goodman offering company and very well recognized in the Detroit area.
    He is proposing the following, but said he will put any brand in that I want for the same cost:

    Keep my AS 2 stage 2 speed furnace, said it has a lot of life in it.

    AC replacement:
    Carrier 24ACB 2.5 Ton Comfort Series
    Amana ASX 16 2.5 Ton.

    He also said they would not replace the A coil with a box unit but rather just a new matching A coil for the unit chosen.
    He said all the condensor coils will have the TXV in them.I see the Carrier comes standard with high and low pressure switchws, and the Amana, low pressure only, not sure how big of a difference that makes.

    Any significant reason in choosing one over the other concerning Amana or Carrier?

    Now, per my request, which I guess I have to look into (I know you folks say it is not worth it in MI) But a 16 SEER 2 stage unit, also my choice of MFR for the same higher cost.
    I see the Amana just requires a 2 stage thermostat which I already have with my AS furnace, White Rogers, but the Carrier may require a changeout of thermostat to go with their 2 stage 16 SEER.

    Any significant reason in choosing one over the other concerning Amana or Carrier if I were to go this route?

    We did look at furnaces as well, and if I were to change one he recommended the Carrier 59TP5, for some extra, a variable speed version, or the Amana Equivelant, both 60,000 BTU. Any thoughts here, his package price was actually not to bad and it would get me some hefty rebates. Don't know as though it would be worth it at this time, He seemed to like the Amana Furnace better than the Carrier though, did not say why.

  12. #12
    Join Date
    May 2008
    Location
    Missouri
    Posts
    3,597
    Check your Amana warranty against others!

  13. #13
    Well,
    Made a decision, a good one I hope.

    Going with the well known and respected company in the Northern Detroit area, partially because of cost, but more that they have 30 + service trucks verces my second choice of the Goodman company with 1, which means I should not have to wait to long if service is needed. These folks also spent a lot of time tweaking around what I was looking for, so:

    Amana AMVC95 Furnace, 70,000 BTU, he calc'd for a 60000, but this model only comes in 45 and 70k verse the Carrier PERFORMANCE™ 96 59TP5 W/ECM motor (the variable speed upgrade was cost prohibitive in the Carrier)
    Amana ASX13 2.5 ton AC with a matching TXV being added per my request on the coil.
    Trion Air Bear filter.

    Install is over 2 days next week.

    Last question, what are the thoughts out there about the usefullness of a UV sanitizer above the A coil? The comapny I am going with said they served no purpose, this is not the feedback I received from our HVAC folks at work, who have installed them in there own homes. If I were to get a non-ozone version, will it actually do anything (I know the ozone is not a good thing)? I read somewhere that it ate the protective coating off the A coil, which does not sound right to me, but I am not an expert on how A coils are made. My real concern is, will it eat up the boot between the top of the enclosed A coil and the duct head and is it worth it?
    (I will install myself on this one)

    Thanks for everyone's input on this thread. I know I flip-flopped on the furance or no furnace decision, but, based on higher efficiency from my 80%, and adding the variable speed with a two stage, sounds like a good upgrade that will pay itself off over the next 6 years or so. I run my low fan a lot on my AS two speed now, to keep the air moving, but it is somewhat loud. The low variable speed sounds like a good solution, also to support the UV light better in more exposure time to the air.

    Thanks again

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