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  1. #1
    Join Date
    Dec 2018
    Location
    Ohio
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    4
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    Temp rise/air flow problem

    Hello guys. I've got an issue with a Thermal Zone 80% gas furnace. Model - TZ81UH104TA . Unit has been installed and working since 2013 without any issues. Now within past week it began cycling on the high limit. Acceptable temp rise range for this furnace is 30-60 degrees. I am getting 70+ degrees of rise. With the high side being checked on supply trunk 2 ft from plenum the highest reading I have gotten is 145 degrees. Fan is set to medium high which is factory setting on this unit. All supplies are open and have good airflow. However, there are NO returns on first floor. This house used to have boiler heat. Only returns are on 2nd floor in bedrooms. I also did a load calc out of curiosity and the furnace is oversized by 10-12 thousand btus. I also found it will run within normal temp rise limits if filter is removed from return and filter door is left open. Even with the oversize furnace I believe I can get this thing to settle in and work with more return air, but before I jump in and go that route I wanted to get another point of view. The thing that makes me scratch my head here frankly is the fact that this unit has run without issue until this year. Being oversized for house coupled to serious lack of return airflow one would think this very issue would have reared it's head far sooner than 5 years down the line.

  2. #2
    Join Date
    Aug 2002
    Location
    Southold, NY
    Posts
    27,224
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    Manual D

  3. #3
    Join Date
    May 2014
    Location
    Bay Area California
    Posts
    26,563
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    Wrong air filter? If unit has A/C, dirty evap? Dirty blower wheel?
    I do a triple evac with nitro to remove non condensables.

  4. #4
    Join Date
    Aug 2009
    Location
    Beatrice, NE
    Posts
    10,736
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    I would not be concerned about 10-12k over since most furnaces are sized in 20k jumps. It may have always run at a 70 degree rise but the limit is finally getting weak enough to where it is tripping. I didn't see where you posted the limit rating but 145 is not hot enough for most limit ratings. Undersized duct is not uncommon but have any registers been closed, tubes crushed, etc. Like BB said look for dirt build up. You have to remember temp rise is for normal operation, limits are for extreme situations like blower failure or air blockage. I had a similar situation several years back, thought there was an issue with the supply (weird plenum) and made some duct changes which did help but not cure the situation. Turned out during a remodel they closed a couple returns they never said anything about.

  5. #5
    Join Date
    Jun 2011
    Location
    NE Ohio
    Posts
    2,892
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    Quote Originally Posted by BNME8EZ View Post
    I would not be concerned about 10-12k over since most furnaces are sized in 20k jumps. It may have always run at a 70 degree rise but the limit is finally getting weak enough to where it is tripping. I didn't see where you posted the limit rating but 145 is not hot enough for most limit ratings. Undersized duct is not uncommon but have any registers been closed, tubes crushed, etc. Like BB said look for dirt build up. You have to remember temp rise is for normal operation, limits are for extreme situations like blower failure or air blockage. I had a similar situation several years back, thought there was an issue with the supply (weird plenum) and made some duct changes which did help but not cure the situation. Turned out during a remodel they closed a couple returns they never said anything about.
    may not have noticed but it could have always been cycling on limit, just now more often if the limit is getting weak

    not saying it cant be done, but I would definitely be questioning the return air duct sizing if all of the return air was trying to be pulled from the second floor, especially if the temperature rise drops significantly and the furnace no longer cycles on limit with the filter and filter door removed ... not to mention, how much return air can you remove from just the second floor bedrooms .... bedroom doors open, closed ? ?

  6. #6
    Join Date
    Jan 2015
    Location
    Iowa
    Posts
    1,696
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    Quote Originally Posted by BBeerme View Post
    Wrong air filter? If unit has A/C, dirty evap? Dirty blower wheel?
    What he said

  7. #7
    Join Date
    Dec 2018
    Location
    Ohio
    Posts
    4
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    Thread Starter
    My apologies, I failed to mention that I checked the filter(was clean) and the evap coil both on top and from the bottom. Evap coil is clean. I also know that this unit hasn't been cycling off and on via the limit because it's a house I am in quite often and the stat has been in control of the furnace and it has been reaching temp even on very cold nights during long run times. As far as the btu rating of the furnace being 10-12 thou more than required, it hasn't come into play but I think something has changed to finally bring all these poor design factors into play. Don't know who installed this unit in 2013 but they didn't do anyone any favors by not advising about the lack of return air. It's been lacking good return air flow from the day it was installed but since it has only recently become an issue 5 years later, obviously some other condition has changed. It's in an unfinished basement with dirt floors. House built in 1890s. I'm leaning to the idea that what little return air there is has somehow become further choked by either dirt/dust infiltration or something has physically gotten into the return panning somewhere and blocked flow. Maybe another piece of panning inside came loose and dropped down between joists(?) I've got it running without cycling on limit now but only with filter removed and filter door open which obviously cannot remain that way. Most of the exposed duct in basement including return panning is very old but someone put new supply trunk in at some point not long before this furnace was installed. At least from the appearance of it. I need to take a closer look from basement at the 1st floor flooring and see if there appears to be any newer wood possibly covering where a return used to be. Bottom line however is getting more return runs to it.

  8. #8
    Join Date
    Nov 2006
    Location
    Athens, Ohio
    Posts
    7,308
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    What kind of filter? I hate 3M Filtrete.
    I agree that more return can only help.
    AOP Rules: Rules For Equipment Owners.

    Free online load calculator: http://www.loadcalc.net/


    There = not here. Their = possessive pronoun. They're = they are
    It's = contraction of it is. Its = the possessive form of it
    Too = also. To = expressing motion. Two = 2
    Then = after that, next. Than = indicates a comparison.
    Questions should end with a question mark "?" Statements end with a period "."

  9. #9
    Join Date
    Mar 2015
    Location
    Hamersville, Ohio
    Posts
    7,281
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    "Unit has been installed and working since 2013 without any issues"

    How do you Know this JC?

    "I also found it will run within normal temp rise limits if filter is removed from return and filter door is left open."

    Sounds like an Return Air problem, initially.

    Look for some Major change in that Return Air, ... Ike Hillary Clinton's E-mails being stashed there.
    Hos 4:6 My people are destroyed for lack of knowledge. Because you have rejected knowledge, I will also reject you, that you may be no priest to me. Because you have forgotten your Gods law, I will also forget your children.


    "You've got to Stand for Something or You'll fall for anything" (A. Tippin)


    Mat_15:24 But he answered, I wasnt sent to anyone but the lost sheep of the house of Israel.

  10. #10
    Join Date
    Mar 2015
    Location
    Hamersville, Ohio
    Posts
    7,281
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    Quote Originally Posted by BBeerme View Post
    Wrong air filter? If unit has A/C, dirty evap? Dirty blower wheel?
    Hos 4:6 My people are destroyed for lack of knowledge. Because you have rejected knowledge, I will also reject you, that you may be no priest to me. Because you have forgotten your Gods law, I will also forget your children.


    "You've got to Stand for Something or You'll fall for anything" (A. Tippin)


    Mat_15:24 But he answered, I wasnt sent to anyone but the lost sheep of the house of Israel.

  11. #11
    Join Date
    Dec 2018
    Location
    Ohio
    Posts
    4
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    Thread Starter
    Quote Originally Posted by DavidDeBord View Post
    "Unit has been installed and working since 2013 without any issues"

    How do you Know this JC?

    "I also found it will run within normal temp rise limits if filter is removed from return and filter door is left open."

    Sounds like an Return Air problem, initially.

    Look for some Major change in that Return Air, ... Ike Hillary Clinton's E-mails being stashed there.
    The unit is in my brother's house.

    "Look for some Major change in that Return Air, ... Ike Hillary Clinton's E-mails being stashed there"

    HA ! You just made my day

  12. #12
    Join Date
    Mar 2015
    Location
    Hamersville, Ohio
    Posts
    7,281
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    "The unit is in my brother's house. "

    Who Installed it?

    And, You might also find files, Disks, Missing people related to the "Trump Russia-gate" in there.
    Hos 4:6 My people are destroyed for lack of knowledge. Because you have rejected knowledge, I will also reject you, that you may be no priest to me. Because you have forgotten your Gods law, I will also forget your children.


    "You've got to Stand for Something or You'll fall for anything" (A. Tippin)


    Mat_15:24 But he answered, I wasnt sent to anyone but the lost sheep of the house of Israel.

  13. #13
    Join Date
    Dec 2018
    Location
    Ohio
    Posts
    4
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    Thread Starter
    Quote Originally Posted by DavidDeBord View Post
    "The unit is in my brother's house. "

    Who Installed it?

    And, You might also find files, Disks, Missing people related to the "Trump Russia-gate" in there.
    Was installed in 2013 and he moved in early 2015. Have no idea who installed it. It looks like a professional job not something done by a home owner. All the sheetmetal piping and wiring is neatly done but they didn't size it right. I'm going over there this morning and get a better look at the duct work.

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