HVAC Guys, how hot is too hot?

The #1 community for Gun Owners in Indiana

Member Benefits:

  • Fewer Ads!
  • Discuss all aspects of firearm ownership
  • Discuss anti-gun legislation
  • Buy, sell, and trade in the classified section
  • Chat with Local gun shops, ranges, trainers & other businesses
  • Discover free outdoor shooting areas
  • View up to date on firearm-related events
  • Share photos & video with other members
  • ...and so much more!
  • jkaetz

    Master
    Rating - 100%
    3   0   0
    Jan 20, 2009
    1,953
    83
    Indianapolis
    New to me house. Drees home built in 2012, Lennox ML193UH090XP48C furnace with a Jackson Systems Z-300-HC-MS zone controller separating the first and second floor. The zone controller is repeatedly hitting the high limit and shutting down the burners. According to the dip switches it is set at 160 degrees. I pulled the zone controller probe and verified that the temp is indeed 160 almost exactly. Even after letting the system run without the controller intervening, the temp stayed around 160 +- 2 degrees. Is this ok? Other info I know:

    • The temp probe is mounted roughly 36 inches above the heat exchanger
    • The limit is tripped and temp remains constant even if both zones are calling for heat
    • Also happens without the filter installed. Filter is a new MERV 8 20x25x4, I couldn't find anything less.
    • All vents are open and seem to have good airflow
    • The bypass damper is mechanical and is open regardless of one or two zones calling for heat.
    • Zone dampers are working correctly
    • The furnace limit does not trip if I pull the zone probe and let the system run continually.
    • The pre-fire air temp was about 75 and the house temp was in the 60's
    • The unit does have 4 fan speeds that can be selected depending on what wire is connected to the heat or cool terminals, currently it is on the medium-low speed for heat and medium-high for cool.
    • Basement was finished by a previous homeowner and I'm afraid of what they've done to the duct work. I can see some of it but can't easily access it without pulling drywall.

    I have a relatively inexpensive manometer on order to try and check the static pressure of the system. I suspect the ducts are undersized but I don't know if I'll be able to do anything about that. An Airtron yahoo checked the system before closing but of course said everything was normal. Probably didn't let it run very long or didn't pay attention.
     

    ChristianPatriot

    Grandmaster
    Rating - 100%
    28   0   0
    Feb 11, 2013
    12,801
    113
    Clifford, IN
    Most gas furnaces I’ve seen discharge in the 130 degree range so yeah 160 does seem high to me. That is a 90+% furnace but it’s only 1 stage heating. Really hard to diagnose a problem like that without putting hands on it. I’m sure you’ve checked your air filter.
     

    jkaetz

    Master
    Rating - 100%
    3   0   0
    Jan 20, 2009
    1,953
    83
    Indianapolis
    Most gas furnaces I’ve seen discharge in the 130 degree range so yeah 160 does seem high to me. That is a 90+% furnace but it’s only 1 stage heating. Really hard to diagnose a problem like that without putting hands on it. I’m sure you’ve checked your air filter.
    First thing I checked. Maybe I'll see if I can lure the resident INGO mouse out with some cheeseburgers.
     

    actaeon277

    Grandmaster
    Site Supporter
    Rating - 100%
    4   0   0
    Nov 20, 2011
    92,860
    113
    Merrillville
    Check the vent/offtake.
    Might be plugging up with spider webs, slowing down the air, causing it to heat more.
    You might have to clean up with a shop vac.
     

    actaeon277

    Grandmaster
    Site Supporter
    Rating - 100%
    4   0   0
    Nov 20, 2011
    92,860
    113
    Merrillville
    I'm not sure I'm following. The intake for the combustion gases or the bypass? The bypass dumps back into the return.

    Where your sensor is, should be where it goes up the exhaust. For me, there's a pipe that goes to my chimney.
    There are cobwebs in there, that caused my sensor to keep tripping.
    I removed a screw and pulled the sensor back just a hair. The sensor is no longer tripping the furnace.
    Later, maybe tomorrow, I'll vacuum out everything. I need to vacuum the condensate drain anyway, because it's plugging, probably also with spider webs.
     

    actaeon277

    Grandmaster
    Site Supporter
    Rating - 100%
    4   0   0
    Nov 20, 2011
    92,860
    113
    Merrillville
    In this drawing, the one labeled "flue vent connector" is where I have spider webs.
    There is flow, just less than it should be
    gas-furnace-proper-vent.jpg




    The metal "pipe" coming off the furnace
    Water%20heater%20vent.jpg
     

    jkaetz

    Master
    Rating - 100%
    3   0   0
    Jan 20, 2009
    1,953
    83
    Indianapolis
    In this drawing, the one labeled "flue vent connector" is where I have spider webs.
    There is flow, just less than it should be
    Ahh got ya. My unit is a 90%+ efficiency model. It has a PVC exhaust vent going out the wall. It is still using interior air for combustion though. I will look for any blockage in the intake though if there is a blockage in intake or exhaust these units will usually fault.
     

    jkaetz

    Master
    Rating - 100%
    3   0   0
    Jan 20, 2009
    1,953
    83
    Indianapolis
    Over fired I would assume. Assume is all I can do over the interwebs.
    Both zone dampers open...???

    Did this just start happaning...???

    I am a bit tire from doing the 1500 today so bear with me. Not a flu issue. You said filters OK. 160* is way to high.
    No problem. Yes, both zone dampers are working, though the temp does not drop even with both open. We closed last Friday so I've been in and out of the house intermittently. It's taken me this long to diagnose and do some initial TS. When I first heard it short cycle I assumed filter but that has proven not to be the case.
     

    Brandon

    Grandmaster
    Rating - 100%
    11   0   0
    Jun 28, 2010
    6,997
    113
    SE Indy
    Now that i think about it we had a similar issue to this. We added the damper the day we replaced their furnace. No issues since.

    It was a 90% - I don't remember the make, second floor, 2 zones.

    Im in install so we dont diagnose... Just rip out and reinstall.
     

    jkaetz

    Master
    Rating - 100%
    3   0   0
    Jan 20, 2009
    1,953
    83
    Indianapolis
    But it’s staying open no matter what? If it’s blowing hot air into the return I could see that raising the supply temp.
    I thought so too, I measured the return air at only 75 though. 75 -> 160 is still nearly a 90 degree rise and out of spec. It's nice and toasty coming out of the vents, but I fear for the longevity of the system if we don't get it cooled down a little. I have some suspicions as to the issue but I'll wait for CM to take a peek.

    :thumbsup:

    Dual zone system with one big single stage furnace is a no-go in my book, but what do I know :dunno:

    Yup. Somebody cheaped out on the install.
    I agree with both of you, but it appears to be how builders are doing zoning to save costs. Blasted cheapskates. I never thought I would see a zoned system without multiple stages yet here one is. Idiots...
     
    Top Bottom