Page 1 of 3 123 LastLast
Results 1 to 13 of 30
  1. #1
    Join Date
    Aug 2012
    Location
    Florida Space Coast
    Posts
    503

    Four Different Manual J's - Same Recommendations!

    1827sf Central Florida East Coast block one story on slab, lots & lots of single pane sliding glass doors and windows, open beamed family room, ducts sealed to within 6% total leakage, R30 added to attic, some windows tinted with 70% 3M film, average annual ACH of 0.40. Roof replaced in 2000 with Energy Star asphalt shinges (light grey).

    I already had 3 different Manual J's, all recommending 3.5Ton based on combined sensible and latent cooling loads @ 0.75 SHR. I very much want to replace the old 1999 Rheem 3.5Ton with a 3Ton to save on electric, if it will keep me cool at design conditions. So when the last contractor came by on Monday to take measurements in preparation for his bid, I told him I really, really, would like the Manual J to prove to me that 3Ton is big enough. I shared with him the results of the blower door and infiltrometer testing and explained all I'd had done recently to improve the envelope, so his data would not be skewed towards a bigger unit. He even over-rated the shading on my glass doors in an attempt to "bump" the Man J a bit lower. I got the results awhile ago, and noticed he'd even lowered the size of my house by 100 square feet, maybe in error, maybe by design.

    Regardless, this Man J also recommended 3.5Ton. Now I'm scared to undersize to 3Ton and skeptical about oversizing to 4Ton to take advantage of 2-stage. Since I'm "done" improving the envelope, I think I've pretty much got my mind made up to go with a single stage 3.5Ton. Leaning towards Broan equipment because parts are easy to get through RE Michel, but keeping an open mind.

    Still need to find that "professional" installer who can convince me that he (or she) will do it right the first time. Someone who can use a manometer to take ESP and verify blower CFM against rated efficiency. Don't need someone looking to take my check to the bank hoping I won't notice the inefficiencies leading to higher than necessary electric bills until it's too late.

  2. #2
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,296
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  3. #3
    Join Date
    Aug 2012
    Location
    Florida Space Coast
    Posts
    503
    Yes, Dan, I'm still interested in the new mid-level iQ Drive released this year. The FT4BG-036K has a nominal cooling capacity of 34800 btu, so with a 40 to 118% variation in actual capacity, it would max out around 41000 btu, which I think I could live with. The contractor who did the last Man J said he couldn't get them yet... maybe by the end of the month he'll be able to quote me a price.

    Still would like to know what 3Ton equipment you have in your ~1800 sf house that gets you a high bill of $130. Sure would like to cut my high bill of $250 in half!

  4. #4
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,296
    Quote Originally Posted by Florida Joy View Post
    Yes, Dan, I'm still interested in the new mid-level iQ Drive released this year. The FT4BG-036K has a nominal cooling capacity of 34800 btu, so with a 40 to 118% variation in actual capacity, it would max out around 41000 btu, which I think I could live with. The contractor who did the last Man J said he couldn't get them yet... maybe by the end of the month he'll be able to quote me a price.

    Still would like to know what 3Ton equipment you have in your ~1800 sf house that gets you a high bill of $130. Sure would like to cut my high bill of $250 in half!

    I have a nice attached villa (although I don't like the windows much) with lower than normal cooling requirements and an 11 year old 10 SEER Armstrong unit.
    Some people may refer to it as a P.O.S. but it sure has performed tremendously in maintaining R.H. at 40%.
    Therefore, I never have to set the t-stat lower than 76'F and can raise it to 80'F+ when away.


    Semi-annual maintenance check probabably helps the performance stay close to peak.
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  5. #5
    Join Date
    Aug 2012
    Location
    Florida Space Coast
    Posts
    503
    Quote Originally Posted by dan sw fl View Post
    I have a nice attached villa (although I don't like the windows much) with lower than normal cooling requirements and an 11 year old 10 SEER Armstrong unit.
    Some people may refer to it as a P.O.S. but it sure has performed tremendously in maintaining R.H. at 40%.
    Therefore, I never have to set the t-stat lower than 76'F and can raise it to 80'F+ when away.


    Semi-annual maintenance check probabably helps the performance stay close to peak.
    Thanks for the response. If I'd thought about it awhile before I bought my detached retirement home, I might have opted for one of the "attached" country club communities in my neighborhood and saved a bundle on grounds maintenance, upkeep, and cooling costs! Like I said, my high bill in VA for a 2400sf, 3-story townhouse was $130, and I kept it at 68* year round! But, one thing I didn't care for with "attached" living arrangements in VA was having common walls with neighbors. One in particular was a royal PITA.

    My decrepit 13-year old POS Rheem holds RH at <40% most of the year. I'd hate having to give that up with a new system!

  6. #6
    Join Date
    Aug 2012
    Location
    Florida Space Coast
    Posts
    503
    Quote Originally Posted by Florida Joy View Post
    Regardless, this Man J also recommended 3.5Ton. Now I'm scared to undersize to 3Ton and skeptical about oversizing to 4Ton to take advantage of 2-stage. Since I'm "done" improving the envelope, I think I've pretty much got my mind made up to go with a single stage 3.5Ton. Leaning towards Broan equipment because parts are easy to get through RE Michel, but keeping an open mind.
    It looks like the phrase in bold is key, since I'm not done analyzing! lol

    I've been over and over the 4 different Man J's trying to determine exactly what it is about my house that makes it a 3.5 ton requirement versus 3 ton. While I cannot see the input values used by the 3 contractors who used their various software programs for their Man J load calc, I can see the values I input to the online Auditor demo (link provided by TeddKidd).

    It looks like I made 2 mistakes on my input that caused the 3.5 ton requirement.

    First mistake: I counted all the sliding glass doors on the SE side of the house as facing SE. Since these doors form 3 sides of a SE facing atrium, only one set of doors actually faces SE (this is the one I tinted with window film)... the second set faces NE, the third set faces SW.

    Second mistake: I misinterpreted the average ACH of 0.40 per the blower door infiltration report and input it as the summer ACH. Then, based on the defaults of 0.60 summer, 0.80 winter, I input a winter ACH of 0.60.

    I went back and corrected the window orientation and the summer/winter ACH (0.30/0.50). Guess what? This new Manual J load calc shows a 2.8 ton cooling requirement!

    So.... now I feel comfortable choosing a 3 ton. I hate to say it, but if you don't do the calculations yourself, who knows what you'll end up with?

    I just received a "reasonable" quote on a Carrier Performance 3-ton, 16 SEER, 13 EER, 2-stage HP, 25HCB636A30 cond matched with FV4CN(B,F)005 a/h. Any opinions?

    Also looking for dealers who can quote the Bryant Evolution 3-ton (Trophy), 18.2 SEER, 13.7 EER, 2-stage HP, 289BNA036****C cond matched with FV4CN(B,F)005 a/h. Any opinions?

    I do have a 3-ton Trane XL20i quote, but I've decided against Trane for the time being, for a couple of reasons. The positive air pressure noise in the ahu, for one. Also discovered I'd have to move the thermostat because the XL950 Comfort Link is too sensitive and errors out if it's placed directly above a return grill.

    Still interested in the new mid-level iQ Drive released this year, but no one in my area has pricing and availability yet.

  7. #7
    Join Date
    Jun 2001
    Location
    Moore, Oklahoma, United States
    Posts
    4,311
    If the poorly installed existing 3.5 ton (which may only be delivering 2.5 tons) is doing the job a properly installed 3 ton (which will deliver 3 tons) should easily handle the load. If the 3 ton calculation is wrong the worst that will happen is you will be over the desired setpoint a degree or two on the hottest afternoons. The unit will easily catch up once the sun goes down and the house will be nice and cool for sleeping. Another side effect is lower power bills from the smaller unit since it will be running more during the catchup phase when it's cooler and can run more efficient. Manual J tends to oversize systems, and you are showing a load of 2.8 tons. A 2.5ton 15 SEER single stage unit will result in the lowest overall bill IMHO. If properly installed it should cool at least as well as your current poorly installed 3.5ton unit. The smaller system will be quieter also.

    Keep in mind most contractors are scared to death from deviating from the traditional 500sqft per ton and will fudge inputs until the end of the earth to get the result they want. 3.5tons =1750sqft, which really close to your house size. Coincidence? I think not.

  8. #8
    Join Date
    Jul 2007
    Location
    Delaware
    Posts
    3,824
    2.5 Ton
    Always here

  9. #9
    Join Date
    Aug 2012
    Location
    Florida Space Coast
    Posts
    503
    Quote Originally Posted by energy star View Post
    2.5 Ton
    No way! I tweaked the Man J to get just below 3 ton as it is. Not willing to take a gamble and go smaller.

  10. #10
    Join Date
    Oct 2010
    Location
    Anderson, South Carolina, United States
    Posts
    7,093
    3 ton IQ drive is the way to go. If they made them in half ton sizes then a 2.5 ton would be perfect for IQ per your manual J calculation of 2.8 tons because they operate up to 118% capactiy, but they are only in full ton increments and you are supposed to size them to 100% capacity. carrier has an inverter drive ac called greenspeed, i think its a little pricier than IQ though.

  11. #11
    Join Date
    Jul 2008
    Location
    Rochester NY
    Posts
    4,735
    Quote Originally Posted by Florida Joy View Post
    So.... now I feel comfortable choosing a 3 ton. I hate to say it, but if you don't do the calculations yourself, who knows what you'll end up with?

    I just received a "reasonable" quote on a Carrier Performance 3-ton, 16 SEER, 13 EER, 2-stage HP, 25HCB636A30 cond matched with FV4CN(B,F)005 a/h. Any opinions?

    Also looking for dealers who can quote the Bryant Evolution 3-ton (Trophy), 18.2 SEER, 13.7 EER, 2-stage HP, 289BNA036****C cond matched with FV4CN(B,F)005 a/h. Any opinions?
    That is poignant, and heartbreaking. It really shouldn't be that way should it? And you STILL haven't been able to get a simple esp test - which is also frustrating and a bit frightening. (Great thing about communicating, IT will tell static at the control. So the more people who understand and buy the good stuff, the harder it is for a bad design/install to "hide".)


    Well you have pretty much summitted, and looking back can see how treacherous the path is. Now the problem will be once seen you can't unsee it, and you'll talk to people that don't get it.
    Welcome to insanity.



    Evolution is Infinity I think. I think you should stretch for the full Infinity/Evolution if you can, particularly if you have any susceptibility to noise (where will the outdoor unit be?). Not sure about the current performance series, but I have had complaints of noise on the 2010. Plus, I think better diagnostics at the control might end up being of value to you. GREENSPEED would be the treat, but they are very preciou$.

    There are a few real Infinity experts here (skip, etc.) that you might want to reach out to if you need better qualified convincing.

    You are going to be blown away by how comfortable your house is. I bet you'll have to set your comfortable setpoint higher. Dehumidification from these units will make current temperature setting feel cold.
    Which makes more sense to you?
    CONSERVATION - turning your thermostat back and being uncomfortable. Maybe saving 5-10%
    ENERGY EFFICIENCY - leaving your thermostat where everyone is comfortable. Saving 30-70%

    DO THE NUMBERS! Step on a HOMESCALE.
    What is comfort? Well, it AIN'T just TEMPERATURE!

    Energy Obese? An audit is the next step - go to BPI.org, or RESNET, and find an auditor near you.

  12. #12
    Join Date
    Aug 2012
    Location
    Florida Space Coast
    Posts
    503
    Quote Originally Posted by tedkidd View Post
    Evolution is Infinity I think. I think you should stretch for the full Infinity/Evolution if you can, particularly if you have any susceptibility to noise (where will the outdoor unit be?). Not sure about the current performance series, but I have had complaints of noise on the 2010. Plus, I think better diagnostics at the control might end up being of value to you. GREENSPEED would be the treat, but they are very preciou$.

    There are a few real Infinity experts here (skip, etc.) that you might want to reach out to if you need better qualified convincing.

    You are going to be blown away by how comfortable your house is. I bet you'll have to set your comfortable setpoint higher. Dehumidification from these units will make current temperature setting feel cold.
    Funny you should mention GREENSPEED here.

    Just received email from the contractor who gave me the "reasonable" quote on the 3-ton Carrier Performance 2-stage last week. He provided an unsolicited proposal on the 3-ton Greenspeed, along with the AHRI certificate. I am intrigued. After Carrier "Cool Cash" and utility rebates, the quote is about 22% more than the Performance 2-stage, but almost exactly the same as the price I had from another dealer on the 3-ton XL20i (with similiar discounts and rebates). Can't compare pricing with the iQ Drive, as no one has been willing (or able) to quote it for me.

    So far, I'm really impressed with this guy, his reputation on Angie's list and how long he's been in business. Also, in querying the county permit website, he's installed a lot of residential units over the past 10 years and has a pretty full install schedule for a small company! Not so with a few others I have proposals from.

  13. #13
    Join Date
    Aug 2004
    Posts
    20
    This is the Ask Our Pro's forum, and only Pro members that have been vetted by the AOPC may post advise here. Please apply to the AOPC today, thank you.

    You can find the rules for posting and qualifications here.

    Further infractions may result in loss of posting privileges.
    Last edited by beenthere; 10-16-2012 at 04:37 AM. Reason: Non Pro * Member

Page 1 of 3 123 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Comfortech Show Promo Image

Related Forums

Plumbing Talks | Contractor Magazine
Forums | Electrical Construction & Maintenance (EC&M) Magazine
Comfortech365 Virtual Event