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  1. #1
    Join Date
    Nov 2008

    Default 2 stage furnace size question

    I am looking at buying a 2 stage variable speed furnace. The heating guy says that with a 2 stage variable speed furnace, BTU size is not so big a deal because the way the furnace operates, when a lower power is needed, it operates at the lower level...To me it seems size and operating at a lower power are two separate and different things. Am I wrong in thinking that these are two separate and different things? Or are they connected and not so different?

  2. #2
    Join Date
    Feb 2008

    Default Re: 2 stage furnace size question


    I think what your heating guy was trying to say is that there are many "not so cold days" during the heating season (such as in fall or spring) when there is no need to utilize the full heat capacity of the furnace & keep it at full blast.

    Heat output is measured in btu's/hour, and single stage furnaces operate at full capacity no matter how mild is the outdoor temperature.

    All furnaces have to be designed to respond to the zero degree weather that comes in the coldest days of January.

    Viewed from this perspective, 2-stage, variable speed makes sense---there's no hot blast of air on mild days, the heat is more evenly distributed, it's easier on the equipment by avoiding short-cycling, & it should save money on the monthly heating bills.

    But I could see a problem if for example the distribution system (the ducts) have been poorly designed, leak, or are uninsulated, & end up delivering cold air to the registers on mild days.

    You would thus have to make sure that all the bugs have been ironed out of the installation before the techs leave the building.

    Also, it has to be recognized that everyone has their own sense of what temperature and humidity level feels comfortable to them; these new systems can be tweaked in many different ways until the customer feels comfortable---so keep after the heating techs to make any needed adjustments to the equipment until it meets your comfort level.

    For more info and background, Google "is a two stage furnace"

    The link below is provided for informational purposes---I have no relationship with this company.
    Last edited by NashuaTech; 11-26-2008 at 04:58 PM.

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