The Advantages of Two-Stage Furnace Installation for Your South Loop Chicago Home

I’ve been getting a lot of questions from South Loop (Chicago) residents about “two stage furnaces” and what they actually do for the end user.  In this post I will look at the difference between a standard furnace and a two stage furnace.

What exactly is a two stage furnace?  Basically it’s a standard furnace with some enhanced functions to the gas valve, blower motor and heating sequence that the furnace follows during the heating cycle.  Although there are many different manufacturers of furnaces, all of them operate in the same basic way, but use different parts to achieve these results.

The following is for informational use only and is not intended as a “How to Guide”. Gremillion Mechanical always recommends that if there is a problem with any complex appliance in your home, you must call a professional service technician trained in the repair of that equipment.

The three main differences between standard furnace and the two-stage furnace are:

  1. Gas Valve –  two stage units will use a valve that can raise or lower the gas manifold pressure (high fire / low fire) while the  standard valve will only have one gas manifold pressure.
  2. Circuit Board –  two stage units will use a circuit board that is designed to learn how your furnace heats your home.   All newer furnaces have a circuit board to control the different functions of the furnace but the two stage units learn about your home while they operate.
  3. Fan Motor –  two stage units have an optional variable speed motor (VSM) that varies the amount of air that is circulated throughout the home.   Standard furnaces do have different speeds for the fan motor, it’s just that they have to be wired for the speed that is appropriate heating or cooling.  They just circulate air according to how they are wired.

There are other small differences in between the standard furnace and two stage furnaces, but the above are the main ones.  Now I will go into some more detail on the above differences:

  • Gas Valve  -  Once a two stage furnace has been in operation for awhile, it learns how to heat your home.  Typically, the furnace circuit board will tell the gas valve to allow about 65% of maximum gas flow to burners for use and will run like this about 80% of the time.  Because of this function, you home will stay more evenly heated in every room of your home while saving you money on energy used by the furnace.  The added bonus of this is the furnace operation is quieter due to the lower fan speeds and less frequent starting and stopping of the furnace itself.
  • Circuit Board  -  Two stage units can have all the bells and whistles.  They require a circuit board that can use all the information that is sent to it to determine how to allow your furnace to operate.  Some higher end units will need a special thermostat that requires extra wiring be installed between the furnace and the thermostat itself.  This can be almost impossible in some existing homes and careful consideration should be made when choosing a two stage furnace.  Getting some extra wire to the thermostat may sound simple enough, but can become a nightmare to try to install in your existing location.  Thankfully, only the higher end two stage models need to have a special thermostat installed.  Many of the two stage furnaces on the market today use information on how your furnace operates and then adjusts the function of the unit to match.
  • Fan Motor  -  VSM (variable speed motor) if installed on two stage furnaces will allow the heating effect of the air, that is delivered into your home, to be of sufficient temperature and volume to heat your home.  When the furnace is in “low fire” mode, the amount of btu’s available to be transferred into the air stream is dependent on two things.  First is how hot the heat exchanger gets and second is the amount of air passing over the heat exchanger.  Most modern furnaces have motors that can be manually wired for a specific speed.  VSM motors, along with their appropriate controllers, will vary the speed of the motor while in operation to any speed needed to satisfy the load.  This translates into electrical savings along with quieter operation and enhanced comfort to the occupants of the home.

Although there are many reasons to install a two stage furnace, there is one small drawback, the initial cost.  Standard 80% and 90% furnaces are common and used in the majority of new and retro fit installations in residential structures.   Because of this fact, they manufacture more of them and thus lowering the end cost.  Two stage furnaces have extra components or more expensive components, coupled with the fact they produce less of them, raises the initial cost of the product.  That being said, the two stage furnaces heat your home more efficiently and thus offset some of the added cost.  I have not personally done the number crunching on the payback period, so I won’t comment on that.

Like a lot of things in life, there are many furnace manufacturers products to choose from.  Gremillion Mechanical has the expertise to help you select the equipment that is right for you and your budget.  Our company has access to almost any manufacturer’s brand of equipment you choose.  Our friendly staff will help you and your family stay warm and comfortable in the cold winter months ahead of all of us.

Chicago Heating Repair
3526 S. Paulina St. ChicagoIL60609 USA 
 • 773-234-4575

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