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  1. #1

    Variable Speed Furnace Blower Motor- yes or no

    We have a an 11 year old two story home that is about 3600 square feet and is currently heated with a Bryant Furnace and a Lennox 5-ton AC unit (we had to replace the builder installed Bryant unit a few years ago). When we built the house the builder did not feel that we needed to have a dual zoned system. We keep the house pretty cool in the summer (about 67 degrees) so the AC runs a lot. The Lennox unit works great and the house stays very comfortable both on the entry level and the upper level. We keep the fan in the "on" position rather than "auto".

    We have 2 cracks in the heat exchanger so we need to replace the Bryant furnace. We are probably going with a Lennox SL280 unit with a variable speed blower. Everything sounds great about the unit but my question regarding the variable speed is whether this will cause the upper level to not stay as cool since the thermostat is on the entry level.
    With our current unit blower being "on" at full speed all of the time I'm thinking that our cooling upstairs is probably more effective. I'm concerned that if the entry level reaches the set temperature and the blower motor goes to a lower speed, the upper level will not stay as cool. My guess is the new lennox will be better in every way than the existing Byrant so maybe this wont be an issue and I know that it will be a more economical unit to run, but at the end of the day if our new furnace causes our upper level to not cool off as well, maybe we should avoid a variable speed motor.

    Any suggestions would be appreciated

  2. #2
    Join Date
    Nov 2006
    Location
    Southeastern Pa
    Posts
    19,534
    My suggestion:

    have the contractor evaluate the needs of the structure and duct system, performing a manual J and manual D calculation. This way, you will know the heating and cooling needs of the home, and whether your ductwork needs to be corrected FIRST.

    A variable speed motor will not give you the expected savings if it is struggling to overcome bad ductwork.

    If your ductwork is correct, and the system sized correctly, you should be able to get your system to provide comfort. You may have to relocate the thermostat.
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  3. #3
    Thanks! Actually, another contractor said that our duct work is actually excellent for the house (not sure how he measured for it which might help explain how we've gotten away without a dual zoned system. I appreciate the quick reply!

  4. #4
    Join Date
    Sep 2002
    Location
    I don't know
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    2,909
    I would say yes - an ecm can save hundreds of dollars per year when the fan is run continuously.
    General public's attitude towards our energy predicament: "I reject the reality of finite resource depletion and substitute it with my own; energy is infinite, we just need an alternative storage medium to run the cars on. The economy can grow indefinitely - we just need to "green" everything! Technology is energy! Peak what?"

  5. #5
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,601
    It can be wired/set so the blower runs at full speed on constant fan. But that will defeat much of the savings amd mentions. On constant fan it will run at 1/2 speed, you won't hear it and you won't feel it but it will cost little. We've only had a couple want more airflow. I did wire our office furnace to full blow on constant fan for better circulation when not heating & cooling.

    But in cool mode, with the extra get up & go the VS motor has, it will likely improve cooling upstairs.

  6. #6
    Thanks for the reply. This forum is great and it's truly helped me make my decision to go with the variable speed motor.

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