Why Should You Consider a Two-Stage Furnace?

September 10, 2023

Our team at Save Home Heat Company continues to write blog posts about advanced gas furnaces such as variable-speed and variable-capacity units for a simple reason, the benefits that this class of furnaces offers include greater comfort, higher efficiency, and quieter operation.

In this post, we’d like to feature one of the furnace designs in this category that we haven’t talked much about lately: two-stage furnaces, a popular, versatile design that’s available in both moderate and high efficiency models. Once again, the broad, high quality Lennox product line will be the focus of our discussion.

What is a Two-Stage Furnace?

In short, a two-stage furnace provides two heating output levels, which are selected automatically, depending on the home’s needs. One of the key furnace components in this design is a two-stage gas valve, which switches from low-fire (70% of capacity) to high-fire (100% output) and back again in response to the thermostat and furnace controls. In addition, the exhaust fan on two-stage furnaces has a 2-speed motor, to match the two different heating levels produced by the furnace.

Lennox Furnace - Inside Sketch - Save Home Heat

In the Lennox furnace line, the main blower on two-stage furnaces, whose job is to circulate air around the home, typically employs either a true variable-speed motor or an electrically efficient, advanced, multi-speed blower motor, both of which offer advantages over conventional multi-speed blower motors – quieter operating levels being one of them.

A correctly specified and professionally installed two-stage furnace operates in low-fire much of the time, allowing the homeowner to reap the benefits of a two-stage system regularly.

The Primary Benefits of Two-Stage Furnaces

Two-stage furnaces offer a variety of benefits and advantages, when compared with conventional, single-stage furnaces. Here’s some highlights:

Lower Gas & Electrical Consumption

Compared to standard, single-stage furnaces with the same efficiency ratings, two-stage units use less gas and electricity. Due to the low-fire feature of these units, overall gas and electrical consumption is lower.

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Help Reduce Temperature Swings & Accomodate Marginal Ducting Systems

In addition, two-stage furnaces can help reduce temperature gradients between different rooms or levels in the home, providing more uniform heating than a conventional single-stage model. This is due to the longer heating cycles, at lower fan speeds and reduced heat output, when the furnace is in low-fire mode. This lengthened, yet efficient, heating cycle allows temperatures around the home more time to equalize. The two-stage design can also help mitigate airflow issues relating to a marginal ducting system. On top of that, these furnaces also reduce temperature swings between heating cycles, tracking closer to the temperature setting on the thermostat.

Lennox iComfort S40 thermostat

Enhanced Indoor Air Quality

When it comes to IAQ, compared to standard furnaces, two-stage units help improve furnace filter, air purifier, and central humidifier performance. Again, this is due to the longer, more moderate heating cycles associated with two-stage furnaces: IAQ products get more time to do their job, and the lower fan speed is better for filtering your air, too!

Quieter Operation!

When operating in low-fire, the main blower and the exhaust fan operate at lower, quieter fan speeds, and even the sound coming from the burners, where the flames are being produced, is quieter. Low-fire in a two-stage furnace translates to quieter operation.

Lennox innovation

Our Most Popular
Two-Stage Furnaces

From highest to less efficient Annual Fuel Utilization Efficiency (AFUE) ratings, here’s an overview of the two-stage furnaces from Lennox that are trending with our customers and that our comfort team are recommending this season. All of the below units have automatically controlled, two-stage gas valves and two-speed exhaust fans. Some have true variable-speed fans, and others have a different, advanced blower design.

EL297V: Our Top-of-the-Line Two-Stage Furnace

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The EL297V furnace from Lennox (replacing the popular EL296V) is rated 97% AFUE and is equipped with a true variable-speed blower motor – the quietest, most electrically efficient, main blower motor available. It affords the most accurate tracking of the thermostat set point, the greatest comfort levels, and the highest efficiency available in a two-stage furnace.

In a variable-speed furnace such as the EL297V, when the main blower turns on, the fan slowly ramps up to the ideal speed to match the home’s heating needs. It then automatically adjusts its speed in very small increments, in real-time, to achieve the most efficient operation and optimal comfort level.

When a variable-capacity furnace (variable heating output, as well as fan speeds), for whatever reason, is not the best fit for a homeowner or a particular home, this unit is a great, high efficiency furnace that customers are choosing as an alternate comfort solution.

EL296E: High Efficiency Two-Stage Heating

The EL296E is rated 96% AFUE and is equipped with Lennox’s exclusive Power Saver constant-torque main blower motor. This electrically efficient, multi-speed fan motor automatically adjusts its speed to optimize electrical consumption and comfort levels, also in real time during operation. It’s the next best thing to a variable-speed blower, and according to Lennox, is up to 46% more efficient than conventional multi-speed motors.

Lennox 80+ plus humid. & AC coil case (10)

SL280V: The Quietest Furnace In Its Class!

The SL280V features an 80% AFUE efficiency rating and a true variable-speed blower, just like the EL297V. According to Lennox and independent industry testing, the SL280V is the quietest furnace in its class. This unit is a very popular upgrade for homeowners whose heating load is not enormous, but who desire the quietest, most comfortable, moderate efficiency furnace available.

Budget-Friendly Moderate Efficiency: The EL280E

This 80% AFUE, two-stage furnace certainly bears mentioning because it provides the quality that we have come to expect from Lennox, combined with the Power Saver main blower motor (mentioned above) found on many premium models – and at a price point that many of our customers find attractive!

Lennox Centurion Award

Denver-Boulder Metro Area Two-Stage Furnace Experts

Along with variable-speed and variable-capacity gas furnaces, two-stage furnaces continue to grow in popularity, and for good reason. To learn more about these enhanced performance furnaces, or to schedule a highly informative, low-pressure, free install quote for your home in the Boulder-Denver area, please reach out to our team today.

Please contact me to discuss my home’s heating and cooling needs!