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  1. #1
    Join Date
    Sep 2006
    Location
    Ohio
    Posts
    469

    Variable speed blowers

    Guys, I need some help here. I'm going to install a 3 ton Heat Pump and AHU system in my own house soon. I'm going to get a Carrier/Bryant/Payne system and was thinking of getting a variable speed AHU. I work on Commercial equipment and don't see a lot of Residential units, so I need your advice. Do the variable speed blowers work good or should I go with a 2 speed blower. My Service Manager told me that a lot of guys are having problems with the variable speed units and parts are much higher. He said that if the duct work is not sized just right, the blower doesn't know what speed to run at. Thanks for any advice you can give me.

  2. #2
    Join Date
    Jul 2009
    Location
    Columbia, MD
    Posts
    3,854
    variable speed on a ok duct system. u can set the airflow to 350cfm if your a little under. helps on humidity problems as well

  3. #3
    Join Date
    Jun 2007
    Location
    Round Rock
    Posts
    3,549
    The problem with variable speed blowers is that they really aren't variable speed unless you use the infinity/evolution thermostat. They are more like 2 or 3 speed blowers. There is the newer furnace which has the semi-variable speed for lack of a better term. It does the same thing as the variable speed does without the special thermostat with a normal thermostat. It still has humidity control and cost's less. The variable speed and semi-variable speed blower motors are both very expensive to replace. I haven't had to buy the newer ones yet, but have seen the price on them when replacing them under warranty. All I gotta say is "ouch" for a wholesale price.
    I like DIY'ers. They pay better to fix.

  4. #4
    Join Date
    Dec 2008
    Location
    Ontario Canada
    Posts
    545
    the ECM 2.3, and 3.0 are true variable speed motors without any special stat, they will vary frequency, and thus rpm to match a pre-programed torque amount under various firing rates, thus delivering a constant precise CFM regardless of variances in duct work.

    When the work they work great, the control modules, at least on the 2.3 models were a little sensitive to power spikes and brown outs, from what I hear the 3.0 model is a little tougher. dont know what carrier is currently using on the models you were quoted, so cant comment on them specifically, but from what I have seen, most manufactures are trending towards the Genteq line-up

    if your going variable speed, make sure you get the 10 year warranty, replacement motors are not cheap!

  5. #5
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,910
    A lot of people think of variable speed as meaning that they(the person) can vary the CFM.

    Sorry, thats not what it means.
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  6. #6
    Join Date
    Dec 2008
    Location
    Ontario Canada
    Posts
    545
    Quote Originally Posted by beenthere View Post
    A lot of people think of variable speed as meaning that they(the person) can vary the CFM.

    Sorry, thats not what it means.
    Ah, yes, you are correct

  7. #7
    Join Date
    Jan 2002
    Location
    Ft.Worth,Tx
    Posts
    4,584
    Quote Originally Posted by LKJoel View Post
    the ECM 2.3, and 3.0 are true variable speed motors without any special stat, they will vary frequency, and thus rpm to match a pre-programed torque amount under various firing rates, thus delivering a constant precise CFM regardless of variances in duct work.

    When the work they work great, the control modules, at least on the 2.3 models were a little sensitive to power spikes and brown outs, from what I hear the 3.0 model is a little tougher. dont know what carrier is currently using on the models you were quoted, so cant comment on them specifically, but from what I have seen, most manufactures are trending towards the Genteq line-up

    if your going variable speed, make sure you get the 10 year warranty, replacement motors are not cheap!
    I have worked on V/Drv for maybe 15 years and have only replaced maybe 3 motors on Geo-Thermal units..They are much more reliable than variable speed motors.
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  8. #8
    Join Date
    Feb 2011
    Location
    Ontario
    Posts
    73
    Quote Originally Posted by beenthere View Post
    A lot of people think of variable speed as meaning that they(the person) can vary the CFM.

    Sorry, thats not what it means.
    Well...actually, the owner can vary the speed with the appropriate knowledge in some cases. I have a Lennox SLP98 furnace with the icomfort thermostat and have adjusted the CFM and DAT by referring to the system installer manual. This was out of necessity as I knew more about the icomfort adjustments than the HVAC installers.

  9. #9
    Join Date
    Oct 2005
    Location
    Pacific Northwest
    Posts
    2,266
    We should call ECM's "variable RPM" instead.

  10. #10
    Join Date
    Dec 2010
    Location
    The Quad-Cities area (midwest).
    Posts
    2,652
    A variable-speed blower motor is the only way to go. They are more efficient, quieter, allow you to de-humidify and are very reliable.

    If the ductwork isn't correct (which is often the case) it will try to compensate and become noisey.

    The ductwork should be checked regardless of the blower motor.

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