What is a Modulating Gas Furnace?

Modulating Gas FurnaceIn the Ottawa Valley, it is often said that if you don’t like the weather, just wait 10 minutes. Ottawa winters vary a lot and with these changing conditions, heating requirement for your home changes too. Furnaces need to cycle on and off depending on the heating needs of the home. This on and off cycling causes wear and tear on the furnace as well as wasting energy. A Modulating Furnaces has a much wider range of heat output than a 2-stage or single capacity furnace. A typical Modulating Gas Furnace varies the heat output by up to 65%. rather than the either/or heat output of a 2-stage Gas Furnace or the on/off of a single stage Gas Furnace, a Modulating Gas Furnace uses the gas valve to make small adjustments to heat output of as little as 1% as required.

Modulating Gas Furnace Function

Variable Speed ECM Blower MotorThe Gas Valve in a Modulating Gas Furnace uses as little gas as required by making small adjustments in the heat output, using only as much gas as is required to maintain the temperature in the home. The Variable Speed ECM Blower enhances this further by adjusting the air flow to match the heating, ensuring that you feel the maximum comfort. The result is a dramatic reduction in temperature fluctuations from your thermostat set point, as well as a more even heat throughout the home. Modulating Furnaces operate very quietly, with efficiencies that can exceed 98% AFUE. In addition, the Variable Speed ECM blower uses a fraction of the electricity required by a typical furnace blower.


Modulating Gas Furnaces are available in sizes to suit any home. They are sized for the maximum anticipated heat requirements, with a little wiggle room for those days that are much colder than the norm. A Modulating Gas Furnace will vary heat capacity from as low as 35% of its full capacity, and will adjust heating in increments as low as 1% to maintain proper temperatures in your home. Modulating Gas Furnaces will rarely run at top capacity, but will operate much as a cruise control in your car. As a result, a Modulating Gas Furnace will cycle on and off much less frequently, but simply varies as required. The result is extremely quiet operation with a superior level of home comfort at the highest level of efficiency possible.


Modulating Gas Furnaces typically require a specialized thermostat to operate as their peak efficiency. These thermostats control the modulation rates as well as additional features such as humidity control and ventilation. Many are Wi-Fi Connected for remote operation. You can add a variety of accessories to a Modulating Gas Furnace. The more consistent operation of a Modulating Gas Furnace will optimize and improve the function of devices such as humidifiers, air cleaners and Heat Recovery Ventilators. Modulating Gas Furnaces cost more than less complex furnaces, but provide a superior level of comfort while using the least amount of energy possible.

Hassle Free

A Modulating Gas Furnace will last a longer that its single or 2-stage counterpart, due to the infrequent on/off cycles and rarely operating at full capacity. Ten Year parts warranties are common, with the heat exchangers typically warrantied for the life of the original owner. Modulating Gas Furnaces make much less noise than older furnaces or even new basic furnaces. The operation of a Modulating Gas Furnace is as simple as a standard furnace, but with a much higher level of comfort and efficiency.


As with any heating system, the ducts need to be properly sized so that they move air efficiently. They are however much more forgive of ductwork that is not ideal. The more consistent heat delivery and the automatic adjustment of the variable speed blower are particularly beneficial in duct systems that present challenges.