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  1. #1
    Join Date
    Nov 2006
    Location
    Dallas, TX
    Posts
    8
    Just had new Carrier Infinity furnace + AC coil installed (4-Ton AC/90K BTU heat) to replace 23-yr old furnace. Attic location, (slab foundation) horizontal furnace.

    Old furnace intake opening was 25h x 18w. New furnace is 16h x 25w. Instead of adapting existing cold air return plenum to match new configuration, parts of existing plenum were simply blocked off so the intake plenum/furnace union is now about 16 x 15.

    I questioned installer at the time and he said if old system had adequate airflow, so would new one. But I'm skeptical as this system serves large downstairs of 2-story house -- 5 large rooms with 10' & 12' ceilings and 1700 sq. ft. total. There are 11 supply registers. House is in Dallas/Ft. Worth.

    Can someone please direct me to some guide or info source so I can tell if the cold air return plenum configuration will allow adequate airflow? Before I call heating contractor to come back and reconsider, I'd like to have info to support any concerns I should have. Thanks.

  2. #2
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,613
    Posting a picture would help us understand.

  3. #3
    Join Date
    Nov 2006
    Location
    Dallas, TX
    Posts
    8
    Thanks, I'll try to get a couple uploaded this morning.

  4. #4
    Join Date
    Jun 2005
    Location
    SW Wisconsin
    Posts
    5,034
    This linked page will furnish some understanding of what might be required as to duct size & other airflow factors.

    http://www.udarrell.com/proper_cfm_b...g_systems.html

    Confer with the HVAC contractor with this info & see what he has to say. - udarrell

  5. #5
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    Ask them to show you the "static"(resistance to air",it can be read on the Infinity Control.

    If it's below .7 or.8 ,it's probably okay.

    Though it could have been made better,that one fitting may not make a lot of difference,though without seeing it ,it's hard to say.

  6. #6
    Join Date
    Nov 2006
    Location
    Dallas, TX
    Posts
    8
    Thanks for the help! I'm learning. I also have photos but haven't figured out yet how to post them.

    Right now the furnace is running often but airflow is low and it's doing a great job of heating the ceilings.

  7. #7
    Join Date
    Nov 2006
    Location
    Dallas, TX
    Posts
    8
    Here is Right to Left flow furnace


    Top View showing that 5" on each side is sealed off.



    Lower plenum sealed off



    Side View showing 5" x 16" sealed off on left side, right side also has 5" x 16" sealed off.



    I will ask contractor for "static' as recorded by furnace. And will also how him the other 2 smaller Infinity furnaces the same company installed in our attic which look much better and use the full furnace access mated to a 20 x 25 filter enclosure.

  8. #8
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    Filter being "closed off" is not a good idea,IMHO.

  9. #9
    Join Date
    Nov 2006
    Location
    Dallas, TX
    Posts
    8
    Dash,

    Thanks for the input. Regarding the static reading available from the Infinity Control, I'm guessing that is from the control on the furnace, not the thermostat. Right? The thermostat is not a Carrier; it's a Honeywell and probably can't track error codes and other data.

    CP

  10. #10
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    No ,it's on the Infinity Control/Stat,which you didn't get with your install.Sorry I just assumed you had the Infinty Control.they could test the static ,with a manometer or magnahelic gauge,test points shhould be between the coil and furnace for the supply and just inside the furnace ,close to the filter.

    Might want to look at upgrading to the Infinty Control/Stat.

    The blocked off protion of the filter will get very little air flow to it,forcing all the air thru part of the filter will increase the static thru the filter,plus the portion being used will get dirty faster.

  11. #11
    Join Date
    Nov 2006
    Location
    Dallas, TX
    Posts
    8
    Contractor doesn't like the Infinity Control because he thinks the furnace works better with standard stat. He says that it (Infinity Control) can keep the burner on low stage with lower fan speed and working way too long to get the heat up to the point where the furnace shuts off. But it may be just a cost issue.

    Judging on the restricted airflow I'm getting and the longer run times, he found another way to accomplish the problem he tried to avoid. And it's costing me more money in filter replacements. Plus, I'm concerned that the furnace will not be able to keep up in colder weather.

    Thanks again. I appreciate your expertise. This forum is an outstanding resource.


  12. #12
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    Some here may agree with your contractor,but I wouldn't.


    Longer run times on low,help even out the temperatures between rooms,keep you more comfortable ,do a better job of filtration,etc.,etc.,IMHO.

    Go with the Infinty control,it will also help dehumidify ,during the cooling cycle.Oh yeah, it will also tell you when that filter needs to changed,based on the filter getting dirty,not just based on time.

  13. #13
    Join Date
    Jan 2004
    Location
    PA
    Posts
    68,793
    Originally posted by dash
    Some here may agree with your contractor,but I wouldn't.


    Longer run times on low,help even out the temperatures between rooms,keep you more comfortable ,do a better job of filtration,etc.,etc.,IMHO.

    Go with the Infinty control,it will also help dehumidify ,during the cooling cycle.Oh yeah, it will also tell you when that filter needs to changed,based on the filter getting dirty,not just based on time.
    Main reason for 2 stage is comfort, longer run times in first stage means more comfort.

    Get the infinity control, and get the comfort you paid for.
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