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  1. #1
    Join Date
    Jan 2014
    Location
    UT
    Posts
    12

    Default Is one furnace ok?

    I know it depends on many things...... but is one furnace typically installed in a 3200 sq ft three story home (basement 1000 and two upper floors 2200) without a zone control? One furnace,one thermostat. It seems to me that controlling over all comfort from just one thermostat on the first level will be tricky/difficult and I'm concerned. Thoughts?
    This is for a home that I am building for myself right now and construction has not yet started, so I don't have capacity etc, although I know that it will be high efficiency.

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  2. #2
    Join Date
    Feb 2008
    Location
    Caledon, Ontario
    Posts
    5,005

    Default Re: Is one furnace ok?

    I'd be installing zone dampers w/thermostats. Guaranteed the temps will differ significantly in the upper floors.


  3. #3
    Join Date
    Dec 2008
    Location
    Maryland
    Posts
    2,778

    Default Re: Is one furnace ok?

    Not sure about Utah. Typically only one furnace (heat) is installed. Builders don't want to spend the extra money. AC is another story. Heat is much easier to distribute in a house's duct system. 3200 sf is not that huge that one furnace can not do the job.

    Two word answer. " SYSTEM DESIGN".

    FHA and AC duct sizing to is critical. Balancing the duct system is also critical. Sometimes it is just easier to install two AC systems to achieve the best results.


  4. #4
    Join Date
    Feb 2008
    Location
    Chicago IL
    Posts
    1,984

    Default Re: Is one furnace ok?

    Yes if you want a crappy system that has air stratification, poor temperature control and overall performance.
    NO, if you actually want a good system. Obviously the needs will vary depending on factors such as insulation levels, windows, window orientation, heights, etc.
    I suggest you consider 2 separate systems so that you get better performance. Even if you do zone dampers which are very nice that square footage would likely need two furnaces in tandem. At that point doing 2 separate systems cost would be offset by easier duct runs and no zone damper cost. Also if one system goes down, you've always got another one to keep the house warm.
    Have your contractor and/or architect do ACCA Manual J & D load calcs along with Manual S equipment sizing. If he doesn't know what that is, find another contractor.

    www.aic-chicago.com
    773/844-4AIC
    "The Code is not a ceiling to reach but a floor to work up from"

  5. #5
    Join Date
    Dec 2007
    Location
    Holladay, UT
    Posts
    565

    Default Re: Is one furnace ok?

    Hi Wayne, What I usually see around here is in new construction they size the furnace for the two upper floors and leave the basement unfinished. When the buyers move in and decide to finish the basement the contractor does not install a second dedicated furnace for basement or upgrade the furnace and install a zoning system but just ties into the ducts that are already there. Usually the btu rating is not sufficient for the added square footage of basement. They know that the basement will most likely be finished but they save money by putting in a smaller furnace. I see it all the time.

    Tom Rees / A Closer Look Home Inspection / Salt Lake City, Utah

  6. #6
    Join Date
    Mar 2007
    Location
    Knoxville, TN
    Posts
    2,446

    Default Re: Is one furnace ok?

    Three years ago I went with a zoned system. I have a 2 story about 2800 SF (basement has its own system).
    The house was originally built with only one system. We could never get the second floor comfortable, so we installed a second system to handle the second floor. The way our ducts were installed, it was fairly easy to split the systems. Both floors were then comfortable.

    Three years ago I was faced with replacing the main unit and had a HVAC guy come out. He suggested we take out the second unit (that was about 9 years old), and put in one unit with two zones. We replaced the original gas unit with 3.5 ton a/c, and the second 1.5 ton heat pump with a single multi stage, multi speed heat pump that is 3 tons. My house is more comfortable that it has ever been. We set the thermostat, and never have to change it. The house just stays the same. Second floor is also very comfortable.
    The projected savings was $800 per year, but for the past 3 years, it has been closer to $1100 per year saving.
    The best thing about multi stage and multi speed is I don't feel the air blowing on my head when I'm at my desk, and barely can hear the unit run when I'm out on my deck.

    I have a separate 1.5 ton heat pump in my 1600 SF basement. The basement has very little cooling need, but I run it to keep the humidity down. More heat load than anything in coldest part of winter.


  7. #7
    Join Date
    Jan 2016
    Location
    Illinois
    Posts
    65

    Default Re: Is one furnace ok?

    As you have learned from the previous replies, you have the opportunity to get this done right. Seize the moment and ask for the design documents for the HVAC contractor and ask a qualified mechanical engineer to review them. He may simply throw them out and start over.
    Let us know how this all plays out.


  8. #8
    Join Date
    May 2016
    Location
    TX
    Posts
    4

    Default Re: Is one furnace ok?

    Hello Wayne,
    I agree with John, you should take advice from a experienced hvac contractor he will guide you well.


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