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  1. #1
    Join Date
    Oct 2019
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    Trying to determine fix vs new and.. who has correctly sized furnace

    So.. our new home furnace is broke- precisely 2nd heat exchanger. I researched ton and many say replace, which we are open to.. thing is, our contractor think our furnace is oversized and that may be the reason of why 2nd heat exchanger is cracked. So he was suggesting 110k btu 2 stage furnace. But, here is fun part- our home’s previous owner is also hvac service business owner. And he had put 120k btu multi speed. It is approximately 9 years old. It is not too old considering this specific brand is built to last 20-25 years.. and this furnace was heating first floor and basement. (2nd floor has its own furnace) So I wanted to ask if we should replace the whole new furnace or fix.

    Here are few facts about our home..
    1. First floor and basement total square foot is approx. 4000 sqft ish. ( they are almost identical in size, may have some difference being basement and first floor)

    2. Back half (about 1500 to 2000) is new addition that has better insulation.

    3. That being said, front half has weaker insulation.

    4. Back half of first floor has floor radiant heating. ( which we been using during winter time, wonder this also the reason why our heater stressed too much..)

    5. Back part of house is south -west exposure so during the day- through out year- it heats up.

    6. We are in Chicago suburb.


    We will definitely do load calculation by professional, but wanted to get some opinions from others and see what others think.. if previous owner had oversized furnace? Or is 110kbtu still be oversized..? Or is120k is being good size and should we just replace part..?

    Any advice would be appreciated!!!

  2. #2
    Join Date
    Dec 2005
    Location
    Cincinnati, Oh
    Posts
    7,326
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    Oversized.

  3. #3
    Join Date
    Jan 2014
    Location
    New England
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    See what load calculation say 1st, before doing anything, no?

    What’s the efficiency level of those two units, 95%

    Part should be under warranty at 9 years old, labor chargeable.

  4. #4
    Join Date
    Dec 2002
    Location
    in a house, Appomattox, Va.
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    what brand? there's a few "gotchas" I've seen out there that caused premature failure.
    Col 3:23


    questions asked, answers received, ignorance abated

  5. #5
    Join Date
    Mar 2018
    Location
    Chico, Ca #StateofJefferson
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    What's the model# and manufacturer of your current furnace and the proposed replacement? Oversized equipment on undersized ducting is par for the course, so it's important to know how much air your ducting is capable of moving at 0.5" water column as that's the sweet spot. Anyone that tells you a ecm blower fixes bad ducting, show them to the door. Is this system zoned? What are you doing for air filtration? System lifespan is determined mostly by the installing company, and not so much the equipment so getting a contractor that can do these things might be the hardest part

  6. #6
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    9,992
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    CHICAGO
    BASEMENT : _____ 2,000 SQ, FEET
    FIRST FLOOR: ____ 2,000 SQ. FEET
    SECOND FLOOR: __ 2,000 SQ. FEET

    Was the house built in 1891 or 2011 ?

    ______________ WALLS __ R-1 __________ R-18
    _____________ CEILING __ R-8 __________ R-48

    _________________ PANE
    _____ WINDOWS _ SINGLE ______ TRIPLE
    ________ AREA ___ 500 ________ 750 SQ FEET

    A.C.H. NATURAL ___ 1.4 ________ 0.24

    Heat Loss in a 1891 house would be about 4X to 5X that of a 2011 house.

    120,000 BTU/HR [ Twice ] for a 1891 house may not be that
    much oversized ( maybe only ~ 170% ) that has not had ANY enhancments.
    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

  7. #7
    Join Date
    Oct 2019
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    Thread Starter
    the old one and new suggested one is 95% efficiency..
    Part was covered.. but since labor is like quarter of getting new one and installation cost.. we are trying to make most out of it.
    But yes, I will ask to do the load calculation first. The rough suggestion came over the email from a comapny who cares our hvac system, without actual load calculation..Just to get a sense of cost to get new one.

  8. #8
    Join Date
    Oct 2019
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    6
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    Thread Starter
    Bazooka joey the old one and new suggested one is 95% efficiency..
    Part was covered.. but since labor is like quarter of getting new one and installation cost.. we are trying to make most out of it.
    But yes, I will ask to do the load calculation first. The rough suggestion came over the email from a comapny who cares our hvac system, without actual load calculation..Just to get a sense of cost to get new one.

  9. #9
    Join Date
    Oct 2019
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    Thread Starter
    Quote Originally Posted by billygoat22 View Post
    what brand? there's a few "gotchas" I've seen out there that caused premature failure.
    It is Bryant.

  10. #10
    Join Date
    Oct 2019
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    6
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    Thread Starter
    Quote Originally Posted by Makeitcold View Post
    What's the model# and manufacturer of your current furnace and the proposed replacement? Oversized equipment on undersized ducting is par for the course, so it's important to know how much air your ducting is capable of moving at 0.5" water column as that's the sweet spot. Anyone that tells you a ecm blower fixes bad ducting, show them to the door. Is this system zoned? What are you doing for air filtration? System lifespan is determined mostly by the installing company, and not so much the equipment so getting a contractor that can do these things might be the hardest part
    It is Bryant, and Evolution Plus 95s Multi speed. Proposed system is Armstrong 96-2v with ssx: 110k btu. I am not sure about the ducting.. didn't thought about it or questioned it would be inefficient since previouse owner was hvac business owner... And yes system is Zoned. air filteration.. for now we are doing nothing other than just filter. Because apprently whatever it came with - the one zaps with electric..? is dead. So we have not replaced or anything...

    and could you please educate me what is ecm blower fixes bad ducting mean..?
    Thank you!

  11. #11
    Join Date
    Oct 2019
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    6
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    Thread Starter
    Quote Originally Posted by dan sw fl View Post
    CHICAGO
    BASEMENT : _____ 2,000 SQ, FEET
    FIRST FLOOR: ____ 2,000 SQ. FEET
    SECOND FLOOR: __ 2,000 SQ. FEET

    Was the house built in 1891 or 2011 ?

    ______________ WALLS __ R-1 __________ R-18
    _____________ CEILING __ R-8 __________ R-48

    _________________ PANE
    _____ WINDOWS _ SINGLE ______ TRIPLE
    ________ AREA ___ 500 ________ 750 SQ FEET

    A.C.H. NATURAL ___ 1.4 ________ 0.24

    Heat Loss in a 1891 house would be about 4X to 5X that of a 2011 house.

    120,000 BTU/HR [ Twice ] for a 1891 house may not be that
    much oversized ( maybe only ~ 170% ) that has not had ANY enhancments.
    Our home is originally built in 1980 but addition was added about 9 years ago which almost double the size of home.. addition part of house has great insulation and all.. but old part has original from when it was built.. so during winter, old part of house is much cooler...when new part is very warm...
    I guess this makes tricky...

  12. #12
    Join Date
    Mar 2018
    Location
    Chico, Ca #StateofJefferson
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    Just to keep it real simple an ecm has the ability to over come(to a point) static pressure above 0.5"wc without losing cfm, a feat an old school PSC motor couldn't accomplish. To do this substantially increases the wattage the motor uses and will significantly shorten the life of the module/motor. Enter Mr. Salestech, who isn't going to tell you about how your ducting is undersized for the equipment and your money is better spent improving and sealing your airflow than buying high efficiency equipment, he's going to stick in whatever with an ecm and get his sale, not his issue when its starts eating motors($$$$)every other year. One of my old service managers told us about how a certain manufacturer taught this "fix" at their equipment sales meetings, just shisty stuff like that.

  13. #13
    Join Date
    Nov 2004
    Location
    SW FL
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    Initial Thought

    Quote Originally Posted by moonyoldy View Post

    Our home is originally built in 1980
    but addition was added about 9 years ago
    which almost double the size of home..

    Addition part of house has great insulation and all..
    but old part has original from when it was built.

    so during winter, old part of house is much cooler …
    when new part is very warm...

    I guess this makes tricky ...
    much cooler … ~66'F
    _ very warm … ~72'F

    " tricky " : SLIGHTLY More complicated

    120,000 BTU/HR Furnaces [ total 240,000 ]
    for a 1980 / 2010 house is oversized by maybe 160% to 280%.

    1980 __ 4,200 sq feet _____ BTU/HR
    ____ ___ 2,100 sq feet * 26 = 55,000 +/- 30%
    ____ ___ 2,100 sq feet * 13 = 27,000 +/- 25% BASEMENT - Underground

    2010 __ 1,800 sq feet * 18 = 32,000 +/- 20%
    ______________ ___ ___ __ 114,000 +30% / -25%

    More later ...
    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

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