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  1. #1
    Join Date
    Aug 2011
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    39

    Rheem Mod gas furnace won't fire on outside air

    I had a 75k Rheem mod installed yesterday to replace a 30 yo Lennox pulse that was working fine, but had a cracked hx. The Rheem was hooked up to the same 2" pvc ducting the Lennox used.

    PVC Inlet: About 15' long, with six 90 degree elbows and 1 Lennox muffler.
    PVC Outlet: About 20' long, with three 90's, 2 45's, and 2 Lennox mufflers.

    The contractor said he called Rheem beforehand to make sure the mufflers were okay, and Rheem said they were.

    The system wouldn't fire when the contractor tried to start it up. They took the upper door off and saw that it was only firing on one burner, then it would shut down because the rest of the burners didn't fire (both with the door off, or when using the outside PVC supply.)

    When they disconnected the PVC inlet, it seemed to fire okay. So we removed one of the plugs on the side of the case so it could draw air from inside the house, and it seems to have run okay for about 4 hours last night. I turned it down after that.

    The contractor's plan is to remove the mufflers, but I'm beginning to wonder if there is some problem with the furnace itself. It was late when they finally got it going, but having it work for one evening is not proof enough to me that it is working as it should.

    For example, what happens when the outside air is very cold or very damp, or it's very windy, or when it's below zero -- will I have more problems then even though they may get it working on outside air supply, because there is some problem with the furnace?

    For example:

    1) Why wouldn't it fire with the upper door off? (I think the fault code was 57.)

    2) Why would one burner fire and the rest not?

    3) The existing PVC is within the angle limits specified in the manual, so why won't it fire with the existing PVC inlet?

    Thanks all.

  2. #2
    Join Date
    Aug 2011
    Posts
    39

    update

    I tried covering the furnace side opening once it has fired, and it continues to run. So it appears it will run on outside air, but not fire on outside air.

  3. #3
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,179
    6 elbows and 2" on the vent are a lot. I'd get rid of the mufflers. Why did he leave them? Lazy!!!!! First, dealers can't call Rheem. They can call the tech rep at their supply house. I highly doubt one would say leave them in.

  4. #4
    alot of 90's on two inch. Im not sure on rheem but I know on Carrier modulating furnaces they recomend that the intake and exhaust be close to the same lengths and amount of restriction. And yes Lazy get rid of the mufflers!!!

  5. #5
    Join Date
    Aug 2011
    Posts
    39
    I previewed Rheem running, and I it was noisy outside. That's why the mufflers are still on. That's why I asked the installer to ask Rheem if the mufflers were okay!
    The installer said the 2" run length and number of angles are in within the limits specified by Rheem. Can one of you point me to Rheem documentation that says the run and number of angles are not within spec?

  6. #6
    Join Date
    Feb 2007
    Posts
    999
    Quote Originally Posted by techjunki View Post
    alot of 90's on two inch. Im not sure on rheem but I know on Carrier modulating furnaces they recomend that the intake and exhaust be close to the same lengths and amount of restriction. And yes Lazy get rid of the mufflers!!!
    Could the pipes be in different pressure zones (length/elbows)?

  7. #7
    Join Date
    Aug 2007
    Location
    Northern VA 38 degrees N by 76 degrees W
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    5,060
    Quote Originally Posted by quiet! View Post
    I previewed Rheem running, and I it was noisy outside. That's why the mufflers are still on. That's why I asked the installer to ask Rheem if the mufflers were okay!
    The installer said the 2" run length and number of angles are in within the limits specified by Rheem. Can one of you point me to Rheem documentation that says the run and number of angles are not within spec?
    Your owners manual and installers guide should have been left with you they are your property

  8. #8
    Join Date
    Sep 2008
    Location
    Western PA
    Posts
    25,671
    Quote Originally Posted by techjunki View Post
    alot of 90's on two inch. Im not sure on rheem but I know on Carrier modulating furnaces they recomend that the intake and exhaust be close to the same lengths and amount of restriction. And yes Lazy get rid of the mufflers!!!
    Warning: The AOPC committee began barring all but Pro* Members from any type of posting in the AOP sections on November 1st, 2011. This post is not from a Pro* Member. It will be tagged for deletion.

    Techjunki,

    This is your second warning.

    Please take the time to review the rules for posting in the AOP forums.

    Thank you

    AOPC

  9. #9
    Join Date
    Sep 2008
    Location
    Western PA
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    25,671
    Quote Originally Posted by ampulman View Post
    Could the pipes be in different pressure zones (length/elbows)?
    This is the Ask Our Pro's forum. In order to post advice here, you must have verified qualifications and have been approved by the AOP Committee.

    You can find the rules for posting and qualifications here.

  10. #10
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,179
    Are these short radius or long sweep elbows? Around here Pulse installers used short and we remove them. Post a picture if you aren't sure.

    Many 90s do make a whining noise outside from the inducer. I doubt a Pulse muffler will do much for that.

  11. #11
    Join Date
    Apr 2007
    Location
    Philadelphia
    Posts
    2,192
    You would need to know gas pressure for us to help you, that is the first thing I would check if i only light off one burner out of several. I would let the installer handle it, Since you are on here asking questions you obviously dont trust them. that's your first problem, Hire people you trust.
    I would also remove the mufflers as the first thing, If you think the Rheem is loud I dont really know what you are looking for in sound of a furnace.

  12. #12
    Join Date
    Oct 2004
    Location
    So Cal
    Posts
    3,524
    Be very careful venting a new 90+ furnace into an existing 2" PVC vent!
    Bit me more than once.

    You posted no model number so I will assume it's a 75k Prestige Mod. The following is based on that.

    The 04 & 06 are the only models approved for a 2" vent. The 07 (75,000 btu) requires a 3" vent & combustion air pipe. Max allowed length for the 3" vent is 60 ft including all elbows. Figuring your 20 ft of pipe & figuring short sweep 90's, without the mufflers you are at 60 feet now & that's with 2". 3" can be reduced at outlet such as using a concentric vent kit.
    Post the furnace model number. I'd bet that furnace needs to be re-vented.

  13. #13
    Join Date
    Apr 2007
    Location
    Philadelphia
    Posts
    2,192
    With a lot of the newer furnaces you have to use a bigger size exhaust if you use outside air intake as well, Example, you can use a 2 1/2" exhause pipe if you are pulling your combustion air from the space, once you add pipe to take air from outside, You have to size up to a 3" exhaust, Make sure he is reading the paperwork right and you have the right sizes.

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