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  1. #1

    Rheem Mod 90 Q's?

    I've been lurking this forum for some time and have really valued the input by each of the various contributors.

    After getting quotes from a number of reputable contractors, I've "bitten the bullet" (only my take on the major $$$ investment) and this coming week my contractor will be installing the following:

    Rheem RGFD-09EZCMS
    Rheem RAPC-036JAZ
    Rheem RHC-TST401

    Given some of the other threads on the MOD about wiring difficulties, settings, or sensors resulting in the MOD not truly performing to its capabilities, are there any specific questions or things to watch for that I should keep in mind for my install, in order to ensure my system will perform as intended. My main concern is having to put blind faith in an installer and not being able to know the difference.

    I'd appreciate any advice that this crew can offer a lay-person.


  2. #2
    Join Date
    Apr 2004
    For the most part, you can look in the blower compartment window when it's in heating mode and you should see a capital H. If you see a lower case h, the unit is not modulating.

    It's not that difficult, but if you set it 1 degree above the room temperature, it will probably fire on a higher setting. You can go watch and listen and over the course of say 20 minutes (depending on the load), it should reduce it's firing rate occasionally. You almost have to use your ears more than your eyes.

    Should you have questions, once it's installed, give us a shout.

  3. #3

    Here are some pics of the install and I'd appreciate any comments from the group. FYI - It's already in the 30's here in upstate NY so we planned going in that we'd be waiting until spring to install the A/C line set and outdoor unit.

    As Doc noted, the furnace is operating in "H" mode and does appear to be modding as there are noticible differences in the level of output. By increasing the t-stat set temp by 6-7 degrees, I can get the unit to ramp up to 100%. However I'm not sure I could tell the difference between 40% operation and 60% operation.

    First question on mod operation; theoretically depending on environmental factors and the relative heat loss from my home, it would seem possible for the unit to call for heat at 40-60% constantly (24/7). Would this present a problem that I should monitor?
    Attached Images Attached Images      

  4. #4
    Here are a couple more picks.

    A second question I had was that we currently have not added either the optional (a) indoor temp sensor or (b) outdoor temp sensor. Would there be any significant advantage or disadvantage to adding one sensor over another? I expect the modding operation itself will smooth out the warmer/cooler spots in my home. But if after we've lived with the system for a little while we still find noticable differences, I was thinking the indoor temp sensor would be a reasonable approach.
    Attached Images Attached Images   

  5. #5
    Join Date
    May 2000
    Indianapolis, IN, USA
    What is that contraption on the exhaust pipe? Certainly not something that comes from Rheem's instructions

  6. #6
    Join Date
    Mar 2004
    Grottoes VA
    Quote Originally Posted by BaldLoonie View Post
    What is that contraption on the exhaust pipe? Certainly not something that comes from Rheem's instructions
    I was wondering the same thing. The instructions do have a tee in the intake for water to drain out before it gets to the furnace, but what he has there will not work, it must be in the horz. pipe.

    Personally I like the outdoor sensor so I can see the outside temperature. Get the ductwork modified and balanced so you will have even temperatures through out the house.
    Karst means cave. So, I search for caves.

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