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I need a new furnace, but know very little about the types of furnaces available. What is the difference between single stage, two stage and variable
Last Updated: 05/04/2010
Answer: Traditional single-stage furnaces are designed to heat your home during the absolute coldest weather in your geographic area. Therefore, they run at their fullest capacity whenever they are in operation, regardless of the temperature outside.
A two-stage furnace has two heating stages: low and high. The low stage runs at a lower capacity, and will heat your home as long as possible until it needs extra power to keep your home at the same temperature set on your thermostat. This is when the high stage kicks in. On average, a two-stage furnace only runs at high capacity 25% of the time it is on.
This multi-level capacity function causes warm air to be distributed into your home more evenly, which helps to reduce air fluctuations. Two-stage furnaces also help to increase energy efficiency on moderate-temperature days since it will, in most cases, remain on the low stage. They will also provide a higher level of comfort due to a steady stream of warm air on the coldest winter days. With two-stage heating, a homeowner does not need to keep adjusting the thermostat.
A "variable speed" furnace does not actually refer to the furnace itself; it refers to the furnace's blower motor. The blower motor is the component that determines the amount of air the blower should deliver to your home. When you have a new furnace installed, characteristics such as the climate you live in and the size of your home determine the speed and airflow that are appropriate for your situation. Because the motor in a variable speed blower motor comes equipped with intelligent technology, it is able to monitor and adjust your blower settings to account for items in your home that restrict airflow, such as ductwork design, furnace location, and dirty filters. With these continuous adjustments, the blower helps your furnace to run as efficiently as possible; they use approximately six times less electricity than a standard conventional blower. This not only helps you to save money, but it also helps to ensure your indoor comfort, regardless of the temperature outside.
While variable speed HVAC equipment provides huge savings and benefits in the winter, it also provides equal advantages in the summer. A variable speed blower can remove up to four times more humidity from your home in the summer than a conventional blower, and therefore increases the efficiency of the outdoor unit. In addition, variable speed furnaces are generally the quietest on market. While the typical payback on a variable speed furnace is 4-5 years, they will last 15-20+ years if they are well maintained with a yearly service plan.
Many HVAC Contractors only specialize in traditional single-stage furnaces; a higher level of expertise and training is required to understand the multitude of components that should be factored into the decision as to which variable speed furnace will be most efficient for your home. Therefore, if you are considering making the investment to purchase a two-stage or variable speed furnace, you should research various HVAC companies to see how much experience they have in installing the type of equipment you are looking for. If you are in the central Ohio region, Columbus/Worthington Air in Columbus are experts at installing variable speed furnaces. In 2009, 75% of the equipment they installed had variable speed blowers.