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  1. #1
    Join Date
    Mar 2005
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    56


    I just had a carrier 2-ton w/ gas burning furnace installed in my home. I am confident with the 2 ton sizing, but the installer put a 3 ton blower on the system Thier reasoning was that since I had my registers in the 9ft. ceilings and had an unheated basement they wanted to get the heated air to the floor. Granted the system has only been in place for a day and I am still feeling it out I feel theat the additional air velocity is too much. It is almost as if the air is going through the furnace peice so fast that it does not have time to get heated. I brought this up to the installed and he showed me where I can ajust the speed of the air handler via jumpers on the circuit board. It has a low,mediam and high one for cooling the other for the heating.
    Please reply back with thoughts on this issue. Is mixing and matching the air handler size a good idea? If the air crosses over the furnace or cooling peice too quickly due to a larger air handler will it not be heated or cooled welll?

    thanks

    Ethan

  2. #2
    Join Date
    Sep 2004
    Posts
    654
    I prefer to run a large blower on low speed, compared to a small blower running on high. Noise is greatly reduced with a large fan turning slower. But if the contractor has designed the system to use velocity to reduce statification, then you're stuck. Even still, I'd try it on the lower speed and see how the comfort is.

  3. #3
    Join Date
    Mar 2005
    Posts
    56

    Thanks for your reply...

    The default speeds which the air handler is currently set to is High for cooling and Medium for heating. I plan to go home and bring the heat speed down to low and see if the air is hotter proving my point of the air passing over the furnace peice to quickly and not getting heated.

    This will also bring the noise level down at the registers.

    I plan on contacting Carrier w/ the SNs of the furnace and airhandler to see if uppoing the air handler speed is ecommended for those units.


    BTW - Pleease define "statification" in the HVAC world?. I looked it up on dictionary.com, but the definition was vauge.

    "use velocity to reduce statification"

    thanks
    ethan

    [Edited by eisenberg on 03-18-2005 at 12:22 PM]

  4. #4
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,358
    BTW - Pleease define "statification" in the HVAC world?. I looked it up on dictionary.com, but the definition was vauge.

    "use velocity to reduce statification"
    I believe he meant to say "stratification", which is a term to indicate stagnant air. When I was a kid my dad would smoke in the house, and whenever the central heat or a/c wasn't running, the smoke from his ciggies would just hang in a horizontal layer about 7 or 8 feet off the floor. The air at that level was stratified...it wasn't moving. When the heat or a/c kicked on, the horizontal layer of smoke would break up, as the air coming out of the registers would mix with the air in the room.

    In your case, I would recommend a heat rise check be done on the furnace at its present blower setting and at the reduced blower setting and that be compared to what the OEM specs for that furnace.

    Did you have a problem with heat reaching the lower levels of the room with the old system?

    I brought this up to the installed and he showed me where I can ajust the speed of the air handler via jumpers on the circuit board.
    The installer should be the one making these changes, if necessary, when he does a start-up. "Start-up?" says the installer. "What's that?" <scratches head>
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  5. #5
    Join Date
    Jul 2002
    Location
    St Paul, Minnesota
    Posts
    3,468
    Caution: Do not adjust air speeds without knowing about temperature rise. You should have a manual from the furnace and it is explained in there. Insert a pocket type thermometer near the furnace return (filter cavity works) and record this reading and then when the furnace has been on for awhile find a spot after the heat exchanger but not in a direct line of sight to the heat exchanger and not right at a 90 degree turn (too much turbulance and reading may not be accurate.) Wait for reading to stabilize.

    Take this difference in the two readings and compare it to the manufacturers chart on the ID plate. (If you read 60, and chart said temp rise should be 45-75, you would be in the middle and where you should be. You don't want to be at the max or min.

    There can be many reasons for too much or too little air flow, (not just blower size/speed), and you should consult the installer if you are out of specified range.

    stratification of air in a room? One of the reasons some homeowners use constant fan is to prevent the hot air from accumulating high in a room and the cooler air settling lower where people are. The constant movement of air prevents this and also continually filters air for better air quality.


  6. #6
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    Post the model numbers of the indoor and outdoor units ,and we can look up the specs,for you ,as far as air flow and how they match up.

    Pat attention to the cautions about temperature rise already given.

    Beware that too much air flow in cooling will lower the system ability to remove humidity from the indoor air.

  7. #7
    Join Date
    Mar 2005
    Posts
    56
    I will reply back with the specs for all units involved

    thanks

  8. #8
    Join Date
    Mar 2005
    Posts
    56

    "Did you have a problem with heat reaching the lower levels of the room with the old system?"

    The old system had radiators which I left in place as a backup. The radiator system is currently disabled

  9. #9
    Join Date
    Mar 2005
    Posts
    56


    ...I have one more question before I get home to post my model#s

    Is it possible for an air handler to move the air to fast resulting in air that is not adequately heated or cooled.

    I would imagine that furnaces and cooling coils are sized to particular equipment. and mixing (adding a stronger airhandler) is not recommended.

  10. #10
    Join Date
    Mar 2002
    Location
    Concord, CA
    Posts
    2,635
    Just to reiterate something that was alluded to eisenberg: An oversized air handler is a VERY good thing in my opinion. I do it routinely and get impressive results. It allows you the option of getting airflow up and at the same time can be turned down to the level of a smaller air handler if so desired. Calling Carrier on this is a waste of time in my opinion. This is a very common and almost always good practice. All manufacturers have multiple approved outdoor unit + air handler combinations. There isn't just one approved air handler for your application. It is certainly possible to have too much air. But the current reasoning for believing so (noise) is not really a good indicator.

    Plus, most ducts are undersized. As a result, a two ton air handler rarely moves two tons of air. Plus, if you live in a dry climate then the extra airflow will increase your AC's sensible capacity. For a dry climate an increase is sensible capacity is effectively an increase in total capacity. Even if you're in a humid climate it's possible that the increase airflow will be fine IF airflow previously was woeful which is not so uncommon. More air on the heat side is often a very good thing in regards to the aforementioned stratification so long as a proper temperature rise is maintained.

    It's possible that you do have too much air. But it's just as possible that the real problem is the noise and where the air is being directed.. The typical diffuser you get from Home Depot or even the wholesaler is garbage. Special order high quality diffusers will allow you to deliver lots of air more precisely directed and at lower noise levels. Though even they're limited by how big the boot is.

    It sounds like the installer was too smart by half. He addressed part of a typical house's HVAC problem by getting airflow up. But he failed to address the other part which is how and where that air gets delivered (ducts and diffusers). And it sounds like he's doing the typical contractor thing, which is to not actually measure the final result. Do we know what the actual delivered CFMs are? Of course, for the few of us contractors that do actually address the whole ball of wax we sometimes get called crooks. When two other bidders focus solely on high margin equipment and the third brings up low margin and seemingly expensive duct upgrades... well the third contractor must be trying to pad the bill, right?

    [Edited by Irascible on 03-18-2005 at 03:16 PM]

  11. #11
    Join Date
    Mar 2005
    Posts
    56
    Please clarify one thing for me. ... I can see that the Carrier air handler is two peices. One being the actual gas furnace peice , the other the blower fan. Here is where I may have lead this thread wrong. I was thinking that my installer had put the 2 ton rated furnace peice with a 3ton rated blower peice. Could that be possible with Carrier equipment?...when my installed purchased the airhandler from where ever I would imagine the it all comes in one box...its not like he opened the box detached the 2ton blower motor ,handed it to them and askedand asked for a 3ton blower motor in return.

    It seems to me that when he told me he mixed a 2ton compressor with a 3 ton "blower" he meant mixing a 2 ton compressor with a 3 ton airhandler....so that would mean the two parts of my air handler (gas furnace & blower) are made for each other.

    ...I hope that made sense

    ,Ethan

    [Edited by eisenberg on 03-18-2005 at 04:40 PM]

  12. #12
    Join Date
    Mar 2002
    Location
    Concord, CA
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    2,635
    Unless Carrier is doing something wacky, it's all one unit. So obviously the combo of heat and fan capacity is inherently approved so long as it's installed properly. There are multiple combinations of BTU capacities and blower capacities offered by all OEMs.

    On a related note, I really shouldn't be using the term air handler. The term air handler is normally used in reference to heat pumps (which are like air conditioners in reverse and don't use gas to heat). While your furnace is indeed an air handler, most in the trade don't refer to it as such.

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