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2 Stage Cooling and 3 Stage heating? Just checking the differences between 1st and 2nd Gen Nest systems, but don't really know what 2 stage cooling or 3 stage heating is or how to tell if your current ac/heating system allows it.
asked by Alex T. Jensen on October 5, 2012
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Showing 1-3 of 3 answers
A
Single-Stage
Single Stage Furnaces have one fan speed, and are available with an AFUE (Annual Fuel Utilization Efficiency) of both 80% and 95%. These furnaces operate at 100% BTU Capacity at all times. These are the most common furnaces, but generally the least efficient and loudest on terms of operation.

Two-Stage Furnace
Two-Stage Furnaces have 2 fan speeds, and are available with an AFUE of both 80% and 92% (or greater) These furnaces operate at 60% BTU Capacity, and progress to 100% as necessary. Two-Stage Furnaces provide a more uniform heat distribution, and are generally a bit quieter than Single Stage Furnaces.

Two-Stage Variable Speed Furnace
Two-Stage Variable Speed Furnaces are available with an AFUE of both 80% and 95% (or greater) These furnaces operate at 60% BTU Capacity, and progress to 100% as necessary via a variable speed motor. Two-Stage Variable Speed Furnaces are much quieter than Single Stage or Two Stage Furnaces. When additional equipment is added to a furnace, 2 Stage Variable Speed Furnaces are the recommended choices for 2 and 3 story homes, and furnaces that also include Air Purification Systems or Heat Pumps.

Three-Stage Variable Speed Furnace
Three Stage Variable Speed Furnaces are available with an AFUE of both 80% and 95% (or greater) These furnaces operate at 60% BTU Capacity, and progress to 100% as necessary via a variable speed motor. Three-Stage Variable Speed Furnaces are much quieter than Single Stage or Two Stage Furnaces. When additional equipment is added to a furnace, Three-Stage Variable Speed Furnaces are the recommended choices for maximum efficiency in 2 and 3 story homes, and furnaces that also include Air Purification Systems or Heat Pumps.
Jeff Schwarz answered on October 12, 2012
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A
"Stage" is a unit of capacity. A system, heating or cooling, has a 100% capacity total and each stage is a fraction of that so... say your cooling total capacity is 3 tons then each stage might be 1.5 tons. this done to better manage output of the system and not overheat or cool the space by running more capacity than is needed. Hope that helps.
John N. answered on December 5, 2013
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A
Whether your system allows it is a matter of existing equipment. Either you already have a two-stage a/c or heat pump or you do not.
Mr. Lauren Berns answered on March 12, 2013
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