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  1. #1
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    Dec 2019
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    New Furnace Sizing

    I am replacing a nearly 20 year old furnace in my home with a Trane Modulating furnace, I have looked at the pros and cons of the furnace already but am still wondering about the sizing of the unit that was on the quote.

    My home is 20 years old located in Northeatern Wisconsin, 2x6 framing with R-19 in the walls and about 18-20" of blown insulation in the attic. All windows are Metal exterior/wood interior casement windows with little to no leakage. The Main floor is just under 1700 s.f. Full unfinished basement to be finished in the near future. Current single stage furnace is 60k BTU's and has done ok for the most part other than frequent cycling during the winter.

    The quotes I was given ranged anywhere from 60k BTU's for the trane all the way up to 90k BTU's for a Lennox, which now has me second guessing what capacity I would actually need.

    Any help is greatly appreciated.
    Thanks,
    Matt

  2. #2
    Join Date
    Aug 2002
    Location
    Southold, NY
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    Have a blower door test done. Then you will know what the infiltration rate is and how to better tighten the envelope. The return on investment is much higher then new equipment!

    Next as you see Contractors Guess at sizing, demand a Manual "J" Load / Loss calculation be performed (you will have to pay for this). Once you know exactly what size is needed then a Manual "D too see if the ducts can handle the airflow requirements of the HVAC System!

  3. #3
    Join Date
    Aug 2009
    Location
    Beatrice, NE
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    Quote Originally Posted by Mseraphine View Post
    I am replacing a nearly 20 year old furnace in my home with a Trane Modulating furnace, I have looked at the pros and cons of the furnace already but am still wondering about the sizing of the unit that was on the quote.

    My home is 20 years old located in Northeatern Wisconsin, 2x6 framing with R-19 in the walls and about 18-20" of blown insulation in the attic. All windows are Metal exterior/wood interior casement windows with little to no leakage. The Main floor is just under 1700 s.f. Full unfinished basement to be finished in the near future. Current single stage furnace is 60k BTU's and has done ok for the most part other than frequent cycling during the winter.

    The quotes I was given ranged anywhere from 60k BTU's for the trane all the way up to 90k BTU's for a Lennox, which now has me second guessing what capacity I would actually need.

    Any help is greatly appreciated.
    Thanks,
    Matt
    As pecmsg says you should have a load done but just for your own knowledge something for you to think about.

    You have a 60k furnace now, at 20 years old it will not be quite as efficient as a new one. If the present furnace cycles at any temp them why would you need anything bigger? Add to this to the best of my knowledge Trane does not make a modulating furnace under 60k so even if a Man J is done and it comes out that you need 38k the 60 in the modulating is as low as it will go, it will just seldom if ever run at 100%.

    Also as pecmsg said you need to make sure the ducts will move the necessary amount of air. I always wonder if a company won't do a Man J what is the chance they will be all that concerned about proper air flow.

  4. #4
    Join Date
    Nov 2004
    Location
    SW FL
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    ACCA MANUAL J CONCEPTUAL

    Quote Originally Posted by Mseraphine View Post
    I am replacing a nearly 20 year old furnace in my home
    with a Trane Modulating furnace,
    I have looked at the pros and cons of the furnace already
    but am still wondering about the sizing of the unit that was on the quote.

    My home is 20 years old located in Northeastern Wisconsin,
    2x6 framing with R-19 in the walls
    and about 18-20" of blown insulation in the attic.

    All windows are Metal exterior/wood interior casement windows with little to no leakage.
    The Main floor is just under 1700 s.f.
    Full unfinished basement to be finished in the near future.

    Current single stage furnace is 60k BTU's and
    has done ok for the most part other than frequent cycling during the winter.

    The quotes I was given ranged anywhere from 60k BTU's for the Trane
    all the way up to 90k BTU's for a Lennox,
    which now has me second guessing what capacity I would actually need.

    Any help is greatly appreciated. Thanks, Matt
    __ BASEMENT IS Nearly ALL Underground.

    ___ 60,000 BTU/HR = Appropriate.

    EXAMPLE:
    LOAD CALC
    _______ HEATING _ 47,600 BTU/HR +/- 20% DT = 78'F

    Q. Sensible COOLING = 18,600 __ DT =13'F
    Attached Images Attached Images   
    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
    May 2000
    Location
    Indianapolis, IN, USA
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    Dan's estimate probably real close. I'd go 60K mod. I'm a Rheem fan on that product, for years they were the only modulating furnace. Lots simpler design than many and the Econet WiFi stat is lots less than a TCONT850. Every size is 98%.

    https://www.rheem.com/product/r98v-r98vb085m521usa/

  6. #6
    Join Date
    Dec 2019
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    6
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    Thread Starter
    Thank you all for the information. Finally made the decision to stick with the 60k BTU. Have the install scheduled for Thursday. Getting the Trane XC95M, and the XL16i A/C installed with a cased coil and a Honeywell F100 air cleaner to replace my old 16x25x1 that I had to replace monthly.

  7. #7
    Join Date
    Nov 2004
    Location
    SW FL
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    Quote Originally Posted by Mseraphine View Post
    Thank you all for the information.

    Finally made the decision to stick with the 60k BTU.

    Have the install scheduled for Thursday.

    Getting the Trane XC95M, and the
    XL16i A/C installed with a cased coil
    and a Honeywell F100 air cleaner
    to replace my old 16x25x1 that I had to replace monthly.
    What does the detailed ACCA Manual J ROOM-BY-ROOM calculation indicate
    as the largest individual room air flow rate?
    Which room ?
    What is the calculated air flow rate?

    What is the calculated air flow rate to the basement?

    Does the ACCA Manual D calculation show that any ducts or duct fitting will need modifications?
    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

  8. #8
    Join Date
    Sep 2008
    Location
    VA
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    Quote Originally Posted by Mseraphine View Post
    Thank you all for the information. Finally made the decision to stick with the 60k BTU. Have the install scheduled for Thursday. Getting the Trane XC95M, and the XL16i A/C installed with a cased coil and a Honeywell F100 air cleaner to replace my old 16x25x1 that I had to replace monthly.
    Good choice with the XC95m, I have that unit for the 1st floor system. I would have chosen a 2 stage or variable speed outdoor unit though.

    What was the Lennox dealer thinking? Why would you up-size a furnace that is already known to have ample capacity? A 90k would have been a waste of money. The modulating ability provides excellent comfort when sized properly. As the other's stated the XC95m lowest unit size is 60Mbtuh.
    "The only true wisdom is in knowing you know nothing" Socrates

  9. #9
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    Dec 2019
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    Thread Starter
    I asked about the 2 stage A/C unit when I got the quote for the system, thought it would be just a little more but it was a pretty large price difference. My neighbor also got a 2 stage unit installed recently and can't tell much of a difference. I couldn't justify the additional cost associated with the upgrade.

  10. #10
    Join Date
    Dec 2019
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    Thread Starter
    Not sure what the lennox dealer was thinking... their quote was considerable higher than I got from anyone else, even with their 70K BTU unit. Feel like I'm getting a pretty good deal overall after speaking with my neighbors and hearing what they have paid for their new systems.

  11. #11
    Join Date
    Sep 2008
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    VA
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    Quote Originally Posted by Mseraphine View Post
    I asked about the 2 stage A/C unit when I got the quote for the system, thought it would be just a little more but it was a pretty large price difference. My neighbor also got a 2 stage unit installed recently and can't tell much of a difference. I couldn't justify the additional cost associated with the upgrade.
    Alternatively, you could add a whole house dehumidifier if your home has trouble maintaining 50% RH. I can tell you from personal experience, the staging equipment works if it's installed and set up properly.

    Prices should be the last thing you look at. Though, we all know price is important, you're paying for labor and incidental materials. Most installations may look similar on paper, but the actual installation procedures can vary greatly. Now, I'm not saying that the high price is going to be the best, but typically a significantly lower price tends to be poor quality. Please understand this: you're not buying a plug and play device like a refrigerator. If you have hvac equipment installed, there are quite a few ways accomplish this task. However, there can be significant differences in the performance and longevity.

    Why???

    Proper installation practices. Everyone wants to think everyone will do it the same, but everyone who thinks this is dead wrong. I can tell you, there are more guys that will throw a system in compared to the guys that will take their time, and make sure it's done correctly.
    "The only true wisdom is in knowing you know nothing" Socrates

  12. #12
    Join Date
    Nov 2004
    Location
    SW FL
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    Quote Originally Posted by Mseraphine View Post

    I asked about the 2 stage A/C unit when I got the quote for the system,
    thought it would be just a little more but it was a pretty large price difference.

    My neighbor also got a 2 stage unit installed recently and can't tell much of a difference.

    I couldn't justify the additional cost associated with the upgrade.
    With Heating Degree Days (HDD) = ~ 600 in NE Wisconsin,
    one would expect < 480 hours of operating time per year.
    __________ I.E. 70 Days @ 7 hours / day

    Appleton __________ 608 HDD
    Manitowoc County ___ 354 HDD (~ 280 Annual operating hours)

    I would NOT recommend 2-Stage A/C for ANY regions with a MINIMAL use.

    COMPARISON : 3,200 HOURS ANNUALLY in SW FL
    ____________ … … 210+ days at 12+ operating hours / day
    ……………………… … i.e. 230 * 13 = 2,990 HOURS
    ……………………… … 7+ Months _ April till November
    ...…………….. … … & ~ 300 hours other months
    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

  13. #13
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    Sep 2008
    Location
    VA
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    Staging equipment is not intended for energy savings.
    "The only true wisdom is in knowing you know nothing" Socrates

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