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Can you use a Nest Thermostat with a Variable Speed Furnace?

Last Updated Jun 29, 2022

We live in a fast paced world where the demands on our time are always increasing. In the middle of the winter, we always want to come home to a warm house whenever possible. The Nest Thermostat does a great job learning our habits and can ensure that our home is warm when we arrive. However, compatibility with furnaces can be an issue. For example, if you have a variable speed furnace, can you use the Nest Thermostat?

You can use your Nest Thermostat with a variable speed furnace. However, if you use a Nest with this system, you may lose out on some of the efficiency gains the furnace provides. Depending on your heating usage, the cost savings from your Nest may or may not outweigh the efficiency benefits of this furnace.

Nest thermostats provide the user with great functionality. The thermostats do a remarkable job of learning your routines and can automatically set the temperature to what you desire based on your usage history. While this can lead to cost savings, it is difficult to foresee substantial cost savings when paired with a variable speed furnace. This is due to how these furnaces are designed; it is important to understand this interaction if you are considering a Nest.

How Variable Speed Furnaces Work

Variable speed furnaces behave differently than a furnace with a single speed fan in a couple of ways:

  • The variable speeds within the motor of the furnace control the flow of air through your home in a more efficient manner than a single speed. 
  • This efficiency leads to cost savings over time and although it is more expensive up front, it typically pays for itself within a few years. 

When purchasing a new furnace, some homeowners will opt for this route if they plan to stay in their home for a few years. The cost savings come in a lower electricity bill due to the higher efficiency of the furnace. As an added bonus, the furnace has a quieter operation than regular furnaces. Unfortunately, for homeowners who have Nest thermostats and this type of furnace, some of the efficiency is lost.

Nest Thermostat and Variable Speed Furnaces Compatibility

The Nest Thermostat is a must-add for homeowners looking to save money. According to Google, however, while the thermostat is compatible with a variable speed furnace, the furnace itself will only operate at a single fan speed when paired with a Nest thermostat. This is not ideal for the efficiency of the furnace as the electricity reduction comes from the usage of variable speeds to optimally control airflow in your home.

Energy Efficiency in a Nest Thermostat and Variable Speed Furnace

Homeowners can enjoy savings from both of these products in the following ways:

  • Nest thermostats will save homeowners money and generally pay for themselves in up to 2 years, saving about $100-200 annually. This type of efficiency is great for homeowners and is the reason why some homeowners have multiple Nest thermostats in their homes.
  • Variable speed furnaces, on the other hand, provide a fair amount more energy efficiency over single speed furnaces. Generally speaking, a variable speed furnace will result in about $300-500 annual savings. 

These savings will depend on usage and the location of your home.  While the up front cost of these products is higher, if you are planning to be in your home for a while, this will more than pay for itself in the long run. Be sure to check with your local heating company for prices of variable vs. single speed furnaces before buying.

Convenience over Cost

As you can see from the cost figures above, a variable speed furnace provides the homeowner with meaningful savings. These savings mostly disappear when paired with the Nest thermostat. Ideally, you would receive the savings benefits from both, however, this is not possible due to the current design. Due to this, some homeowners may decide to forego a learning thermostat in favor of the old school “turn the heat down when you leave, up when you arrive” strategy. 

Following this old school strategy, however, completely negates the important convenience benefit that owning a Nest thermostat will provide! One of the main reasons you purchase one of these thermostats is to have your home warm when you need it and cool when you do not. If you are not using one and have to turn the heat on when you get home, you missed the opportunity to walk into a warm home ready for much needed comfort after a long day.


Nest thermostats and variable speed furnaces both provide energy efficiency for homeowners who install them. Homeowners who have both, however, will lose out on some of the efficiency benefits that a variable speed furnace provides. Determining how important the convenience of a Nest thermostat is relative to these cost savings is a key deciding factor when looking to install these products.

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