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Three Types of Gas Furnace Systems

Written by All Comfort Services | October 25, 2017

Most homeowners don’t know where to begin when replacing a gas furnace, and they are often confused about where the furnace is located and call it a heater instead of a furnace. (In the home-heating world, a heater is considered an electricalportable space heater versus a whole home heating system called a furnace.)

In order to make choosing a furnace system easier, here are the three common types of residential home furnace systems and a few pros and cons related to each type.

1. Single-Stage System

This is the most widely used system in Midwestern homes that was first developed in the 1930s using inexpensive oil and gas. A single-stage system has a basic on and off operation. When a house cools below the set temperature on the thermostat, the furnace will run at full capacity.


  • It’s the least expensive system to purchase.
  • Purchasing a new system can save money on the heating bill.
  • Updating from a system that was installed over 20 years ago will improve energy efficiency.


  • The system runs on or off. It is designed to meet the coldest winter conditions at around 30 below zero. In other words, it doesn’t matter if it’s 10 below zero or 50 degrees outside, it will run on at full capacity.
  • When temperatures reach around 25 to zero degrees, which is most of the time in Wisconsin, the system is oversized for weather conditions.
  • When temperatures are moderate, the furnace clicks on and off while repeating at short intervals. This is called short cycling. Short cycling creates hot and cold areas in the home.
  • In most cases, single-stage systems are a bit noisier than two-stage and modulation systems.

A single-stage system can provide the needed heat, but it isn’t the most comfortable system.

2. Two-Stage System
The next level of comfort is a two-stage system. Essentially, it operates with high or low settings versus one high setting as in a single-stage heating system.


  • Two-stage systems run at the amount of energy needed. When the thermostat registers a heat change in the home, the two-stage furnace adjusts and uses smaller amounts of energy to satisfy the temperature.
  • When temperatures in Wisconsin reach 20 to 30 below zero, a two-stage system will give the appropriate change in heat to meet home comfort needs.
  • The furnace can adapt to modulate temperatures from 25 to zero degrees, which is a majority of the time.
  • The two-stage furnace operates longer in moderate temperatures to eliminate hot and cold spots and gives a more even flow of heat in each area of the home.
  • Cleaner indoor air results. The two-stage system operates more continuously, giving the filtration system a chance to filter more air in the home.
  • Running a two-stage system is quieter.


  • It’s more expensive to purchase initially, but saves more money over the long run.

If choosing a two-stage is budget-friendly, it will save money and provide more comfort than a single-stage furnace.

3. Modulation System
A modulating or variable-capacity system includes a variable-speed blower with a computer-controlled thermostat. This type of system wasn’t available 5 years ago and this technological advancement has benefits.


  • A modulating system adjusts to the heat needed and will automatically maintain a constant temperature.
  • It saves energy using less energy to run. It only uses the energy it needs when it needs it.
  • It provides the most comfort of all furnace systems, keeping homes at optimal temperatures all the time.
  • Modulating systems have a variable speed blower which will vary air flow as determined by the temperature of the furnace and will provide nice even air in your home.


  • The upfront cost is more expensive than a single-stage furnace but over time will save energy and have more comfort.

Single-stage, two-stage, and modulation systems provide a reliable solution for home heating.

Call us today at 608-838-7300 to schedule a free appointment with an All Comfort Services Comfort Consultant to learn more about furnace system options.

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