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skaterrobb Member Posts: 7
edited November 2021 in Gas Heating
I've been trying to do the math can't get it or figure out what kind of lp orifice size I need
No one in my area professionaly seems to know anything
This is the info found on the sticker inside
I'm just trying to keep my kids warm
 Model: M7TL 045A BW
Serial: M7G161212741
0-4999ft(1524m) above sea level
Max input 45000btuh/29000btuh
Out put 42750btuh/27550btuh
Gas supply pressure
Max 13.0
Min 11.0
Manifold 10.0
External static pressure 0.3
Where I live 298ft above sea level
Please and thank you


  • Steamhead
    Steamhead Member Posts: 15,983
    Is this a Miller/Nordyne furnace? One would think if you called the manufacturer they'd be able to provide the proper part number.

    Where are you located?
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    EBEBRATT-Ed Member Posts: 13,422
    edited November 2021
    When a furnace runs on LP gas the gas pressure on the OUTLET side of the gas valve should be 10" of water column. The LP INLET pressure to the gas valve should be 11-13" water column.

    The correct size orifices should be installed (or should have been installed) when start up was done

    As far as I know, most all furnaces are shipped with natural gas orifices and the propane orifices and maybe a new spring for the gas valve must be installed before start up.

    I looked on line for the manual and it didn't come up but I didn't look that hard.

    If you have the manual it should list the orifices for natural gas or propane.

    Is this a new install or existing? What problem are you having?
  • skaterrobb
    skaterrobb Member Posts: 7
    The Original furnace died and a neighbor gave us the one I'm asking about
    ya I've been looking for the manual for 2 yrs and never came with one
    Where the flames are that compartment gets to hot and sets off the safety switch
    3 orifices the last one the blue flame won't contain it's self into the burner tube
    There other 2 orifice are size 60 and 59 but the last guy we had look at drilled them so I don't even know what size they really are the orifice not working is a 55 but drilled
    From what I can put together a #56 0.56mm should work
    Just trying to provide what info I do have

    HVACNUT Member Posts: 5,023
    I understand you want to keep your kids warm but let's concentrate on keeping them alive. 
    Don't alter and run the furnace at all without it set up to manufacturers specs, and then testing combustion. 
    Does this furnace match the load for your house?
    I'm afraid to ask for pictures. 
  • skaterrobb
    skaterrobb Member Posts: 7
    I've tryed finding professional 3 of them just said I dk 1 did something couldn't explain thoughabd our provider Johnson and Johnson I knew more then the guy they sent out Ive been fighting with this furnace for 2 years trust me I'm to the point I would be happy just to find a pro that would know something
    I'm located upstate Oswego NY
  • skaterrobb
    skaterrobb Member Posts: 7

    EBEBRATT-Ed Member Posts: 13,422
    Your first post mentioned LP gas. If your on LP those orifices could be too large. It tells you right on the nameplate "FACTORY EQUIPPED WITH #49 ORIFICES FOR NATURAL GAS"

    What are you burning?

    The manual is attached. Go to Nortek global and search "technical literature"

    Call Nortek at 800-422-4328

    They can tell you where to get parts and maybe find you a contractor
    EBEBRATT-Ed Member Posts: 13,422
    The correct orifice size and gas pressure for propane are detailed in Table 11 in the manual depending on your height above sea level
  • skaterrobb
    skaterrobb Member Posts: 7
    Burning propane
    Ive stuck half of my body inside looking for the manual can't find one online but I will use that number  if I could I would switch to natural gas but for some reason can't
    I have looked up tables but I'm so unsure of my measurements I understand how risky this **** is I'm not having fun lol
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 5,594
    edited November 2021
    This furnace is designed for use in manufactured housing. Here is the technical infor for your furnace.

    Your I/O manual is here

    And your orifice sizes need to be looked up on a chart like this one

    That furnace should have a gas valve with a two position regulator. you need to set the regulator in the gas valve to NAT or LP based on the type of gas you are connected to.

    The correct drill size orifice for LP is a 29
    The correct drill size orifice for Natural gas is a 46

    In order to know what drill have, since the orifices you have may have been drilled out, is to get a machinist numbered drill set. ...OR... purchase the correct size orifice from Nordyne or a supply house that sells Nordyne parts.

    Combustion test is difficult on this furnace because there is no place to drill in the vent pipe for combustion testing. the vent connector is inside a concentric inlet pipe attached to the top of the furnace. You just got to go with the factory settings in many cases. I have on occasions places a 3/8" copper tube thru both pipes in order to get a combustion reading on a problem job. but for the most part, you just set it and look at the flame thru the sight door, to see if it is blue.

    The LP company or the Natural gas company will have a really old service tech that knows how to set them up. If not change LP companies. If natural Gas supplier does not have a experienced tech then I don't know what to tell you.

    Hope this helps.


    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
    EBEBRATT-Ed Member Posts: 13,422

    I don't know what more we can do. I posted the entire manual attached to my post above. You asked about orifices and gas pressures for propane it's all in the manual. All you need to know is you city height above sea level to select the correct orifice. All the information to start and adjust the furnace is in the manual

    Your really going to need some technical help. I suggest you call Nortek tomorrow. I am sure someone in your area is a Nortek dealer that they can point you to. Have then give you a few names.

    If you strike out go to a local heating supply house if you can find one that sells Nortek even better and have them make a few suggestions on who can service the furnace.

    You need this fixed and a combustion test done
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 5,594
    edited November 2021
    I just was reading the manual and realized that this is a 2 stage condensing furnace. I wonder if the thermostat is connected to stage one or stage two? Do you have a 2 stage thermostat? if you have a one stage thermostat you can connected to stage one and two in order to get full capacity. 45,000 is not very big and if you are only firing on stage one then you won't get much heat out of it. check the thermostat wiring! you may need to add a jumper or remove a jumper

    This is on page 22 of the manual

    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • Ironman
    Ironman Member Posts: 7,119
    The OP stated that he’s 298’ above sea level. According to the I/O manual that Ed posted, 1.1mm orifices should be installed and the manifold pressure should be 4.2” on low fire and 10” on high fire.

    Find a gas tech that can take this info, get the correct LP conversion kit and set it up right. No drilling out orifices.

    This is very simple procedure for a competent tech.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • Derheatmeister
    Derheatmeister Member Posts: 1,424
    Beside all of the Orifice and gas pressure/ combustion test and adjustment one should not turn a Blind eye to the Blower speed setpoint which can affect the delta Tee between the supply and return column
    Wrong Blower speeds can also affect the combustion and can have negative affects on the HX.
  • skaterrobb
    skaterrobb Member Posts: 7
    @Derheatmeister I have been trying to figure that out to one guy set the fan on high and it was like a tornado in my place 😑 wish I knew how to read the table I understand the 1 on 0 off just where do I find the numbers I need
  • skaterrobb
    skaterrobb Member Posts: 7
    @EdTheHeaterMan yes I do have a second stage stat and the peg on the mother board is set to 2 stage

    I did see the link everyone is leaving thank you and I am using the info ordered some parts
    I have been using repairclinic.com
    Website could be better but I've never had a problem  with them
  • Derheatmeister
    Derheatmeister Member Posts: 1,424
    edited November 2021

    @Derheatmeister I have been trying to figure that out to one guy set the fan on high and it was like a tornado in my place 😑 wish I knew how to read the table I understand the 1 on 0 off just where do I find the numbers I need

    As you can see from the Name plate the temperature Rise is from 30F to 60F and the max temp is at 160F on the supply column...IT May be time to drill holes in the supply and returm duct work ,check the delta tee (Temperature difference between the columns) and adjust the speed accordingly...You can use a regular pocket type thermometer for this!
    And as allways..... Make sure you have a good unexpired Carbon monoxide detectors installed in the house !!
    Better safe that sorry..