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  1. #1

    Question RGRM-10EZAJS and RARL-049JEZ Oversized ?

    This has been a long process of getting bids and information and now have a system installed and don't know if I need tuning or a replacement system. My fear is that this system is oversized for the property.

    Denver Area
    Home that was converted into 3 apartments
    1892 two story 4 bricks thick - 1800 Sq Ft
    The old porch was added on and ducts were added at some point 500 SQ ft
    Once common heating forced air system in the cellar.

    Displaced thermopride 162K input furnace probably 40% efficient (only saw it work briefly)
    Property used to have a coal furnace years ago.
    Installed RGRM-10EZAJS and RARL-049JEZ and NEST thermostat (1st floor)
    Heat load document from the installer was 60K in a pie chart
    APRILAIRE media filter, and bypass humidifier

    1st floor two double sided heat vents 1 larger return
    2nd floor, 4 heat vents (12 in round return added to this floor up high with this installation)
    Rear porch apartment 500 sq ft, had two supples and not returns (added 1 return and 1 supply)

    Issues:

    Not sure how the selection of my unit size was determined

    2nd floor is 66-67 degrees when 1st floor is 70 degrees
    Addition is 66-67 degrees when 1st floor is 70 degrees
    2nd floor 12" round return is LOUD (wind noise)

    After installation furnace wind noise was LOUD especially the added return. I thought the benefits would be quiet operation. I asked if the blower could be slowed down. With the dip switches they changed it from 1400 CFM to 1150 CFM with of course increase in TEP rise, same BTU's. Same fan speed for 1st and 2nd stage by design.

    Furnace could not be raised off the floor due to height restrictions and A/C coil. All of returns enter into the fight side of the furnace thru the filter.

    My theory is this is an old house with small and few ducts from the old coal furnace and installing this size of the furnace means high CFM to cool the exchanges resulting in lots of noise. Looking at the literature seems a smaller unit could have been selected that still would have supported 4 ton blower for A/C.

    Questions in my mind. Should this be downscaled to 90 or 75 K 2 stage unit
    Should the returns be piped into each side of the furnace to quiet the return via another aprilaire filter
    Static pressure (don't know what it is)
    Do I need another supply in level 2
    Would a 90K 2 stage running at 850 CFM be quiet enough
    i was shooting for a well balanced system rather than a complicated three zone system with bypasses etc

    Any input would be appreciated, or let me know what PICS I can supply. I have not called the installer back until I am a bit further educated here. It's not quiet or comfortable. Installation was careful, ducts all sealed, things done tidy, good reputation installer, just not sure this is sized or tuned for my application

    Thanks !

  2. #2
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,928
    The idea of a 2 stage furnace is to have a slow gentle heat in first stage. Which also tends to help even out the heat in a house. Running it at the same CFM as second stage defeats that.
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  3. #3
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,095
    The furnace on high fire or cool will want to move around 1600 CFM. If you don't have a big duct system it will be noisy. I don't think that furnace will slow down to 1150 CFM on high heat, it would overheat and shut down. There is minimal control over heating blower speeds to protect the furnace. The 09 would want to move similar air. If you stepped down to the 07 with a 3 ton blower, you'll run around 1100 on high as I recall and be much quieter. But max out at a 3 ton A/C. But in your climate that may be all you need anyway.

    If the heat loss was 60K, the contractor was a moron for putting in the big furnace. And if the heat loss was that low, the 4 ton was likely as grossly oversized.

  4. #4
    Quote Originally Posted by beenthere View Post
    The idea of a 2 stage furnace is to have a slow gentle heat in first stage. Which also tends to help even out the heat in a house. Running it at the same CFM as second stage defeats that.
    That is what I thought. But a variable speed furnace really is only variable 2 times, slow startup and slow ramp down. Those are very short segments to avoid the noise of instant burst. After that it tries to run at a fixed CFM as defined by the dip switches on the control board. When you pick the CFM it is the same for stage one as well as stage 2. The difference being in my case, stage 1 delivers 73K BTUS where stages two give more gas and delivers 97K BTUs, My speed choices are 1400, 1200, 1250, 1050. However 1050 would deliver 70 degree temp rise on stage 2 which is pretty high.

    Cooling speeds are independent of these "fixed" speeds on a variable speed furnace.

  5. #5
    I think you are correct and my ducts are too small. If the heat loss is 60K and you are selecting a 2 stage furnace which do you select 50/70. 52/70, 63/84 or 73/97 all in KBTU's.

    The heat loss was based on the 1800 main structure and did not account for the 500 sq ft addition. I should add that.

  6. #6
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,928
    Quote Originally Posted by makeithappen View Post
    That is what I thought. But a variable speed furnace really is only variable 2 times, slow startup and slow ramp down. Those are very short segments to avoid the noise of instant burst. After that it tries to run at a fixed CFM as defined by the dip switches on the control board. When you pick the CFM it is the same for stage one as well as stage 2. The difference being in my case, stage 1 delivers 73K BTUS where stages two give more gas and delivers 97K BTUs, My speed choices are 1400, 1200, 1250, 1050. However 1050 would deliver 70 degree temp rise on stage 2 which is pretty high.

    Cooling speeds are independent of these "fixed" speeds on a variable speed furnace.
    Variable speed blowers are not suppose to be use to use the same CFM/speed for first stage as for second stage. You are misinformed, and your furnace is not set up right. Running too high of a CFM in first sage can cause condensation in the primary heat exchanger and rot it out.
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  7. #7
    I'm looking at the manual that came with the furnace page 48 . Two position dip switches control the CFM exactly for stage one and stage 2. Stage 2 always delivers more BTUS to the home because it is the gas burner that provides higher output. If I can figure out how to post it I will.

  8. #8
    Join Date
    Nov 2000
    Location
    Eastern PA
    Posts
    68,943
    You have a mess that cannot be fixed. You simply have too much overall heat, too much overall cooling and too much overall air.

    It doesn't sound like anyone involved in the application and sizing process understands that staging is only for comfort and that sizing MUST be done based on TOTAL system capable capacity, not based on any low stage with extra "just in case".

    There is no fix for your issue other than having the proper sized equipment installed.
    Government is a disease...
    ...masquerading as its own cure…
    Ecclesiastes 10:2 NIV


  9. #9
    100% Agree. It appear to be the wrong equipment. For heat loss, cooling as well as probably for the duct size.

  10. #10
    What is very frustrating to me as a consumer is I was up front with what I wanted. In that I wanted a quiet low running system and did not want it to be oversized. Amazing I had 5 bids from reputable large HVAC contractors in the industry and their sizings went fro 80KBTU to 120K BTU's. Seems there is no science behind their work. This last one said they complete the technical sizing right before install. Had I known they were going to put this in I would have put a stop to it. It will be removed now and corrected.

  11. #11
    So, setting aside the duct capabilities, CFM for one moment and we just talk about energy. If the heat loss calculation for a property is 60K what size of a 2 stage furnace is optimum? Sized to match at low, high or split down the middle?

  12. #12
    Quote Originally Posted by beenthere View Post
    Variable speed blowers are not suppose to be use to use the same CFM/speed for first stage as for second stage. You are misinformed,....
    I do not believe your statement to be true. Is it possible you could provide some facts here. I am not an HVAC tech but I read the manual in the sections for setting the CFM and temperature rise and I do not believe that the blower speeds for Low and High fire can be set independently.

  13. #13
    Join Date
    Mar 2006
    Location
    The South
    Posts
    2,189
    Make it Happen

    Can't add much to what's been said. Curious though. What mdl thermostat was installed? This furnace for optimal operation works best in a true 2 stage thermostat that controls heating stages not a timer on control board.

    IMO

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