What’s the Difference Between Single-stage, Two-stage and Variable-Speed Furnaces?

Furnace technology has come a long way in the last two decades. Energy-efficiency is now a preeminent concept in the HVAC industry, which is great for you as a consumer since better energy-efficiency translates to lower heating and cooling costs.

If you’re in the market for a new gas heating appliance, you’ll be able to choose from a single-stage furnace, two-stage furnace or variable-speed furnace. Once you know what those terms mean, you’ll be able to make the right decision.

What are Single-stage, Two-stage and Variable-Speed Furnaces?

Single-stage Furnace

The single-stage furnace is the most basic type of heating appliance. It has a fixed gas valve and a single-stage motor, and when it fires up it will run at 100-percent capacity at all times.

Two-stage Furnace

In contrast, a two-stage furnace has a two-stage gas valve and a dual-speed motor. On its ‘Low’ setting it generally runs at somewhere between 60 and 68 percent of capacity, in comparison to 100-percent capacity when it operates on ‘High.’

With a two-stage furnace you won’t be required to control its two settings manually. Your heating system will make that adjustment automatically, starting out in ‘Low’ and only shifting to ‘High’ if thermostat targets aren’t reached within a few minutes.

Variable-speed Furnace

A variable-speed furnace is more flexible and adaptable than either of its rivals. Its blower motor can operate at multiple speeds, shifting up and down in response to evolving temperature situations. Relying on the most advanced HVAC technology, a superior variable-speed furnace can adjust its performance intensity in relatively small increments.

Benefits of Multiple-Stage versus Single-Stage

On a scale of energy-efficiency, the two-stage defeats the single-stage furnace and the variable-speed furnace surpasses both.

Single-stage furnaces will blast away whenever they’re turned on, with no variation in intensity. Conversely,  two-stage and variable-speed furnaces will run on high for no more than 20-25 percent of the time, since most weather conditions don’t require such intense heating.

The benefits you can enjoy from choosing a two-stage or variable-speed furnace include:

More Consistent Temperatures

Because they operate on lower settings the vast majority of the time, two-stage and variable-speed furnaces stay on longer and therefore are able to distribute heated air more evenly throughout the home.

A single-stage furnace will heat up the room with the thermostat more quickly. But they tend to shut down before they’ve adequately heated more remote locations in the home.

Less Noise

This isn’t something you’d necessarily be thinking about while evaluating the possibilities. But once your new furnace is installed and running, you’ll certainly notice the noise it makes, and appreciate the relative quiet of a two-stage or variable-speed furnace humming along at a lower capacity.

Better Indoor Air Quality

The secret here is the longer running times for two-stage and variable-speed furnaces. The longer they are in operation, the more thoroughly a home’s air will recirculate, and with each round trip that air will pass through the furnace filter one more time. This results in a more thorough scrubbing, and a level of air purification that a single-stage furnace can’t duplicate.

Increased Furnace Lifespan

One of the characteristics of a single-stage furnace is short cycling. That is, it shuts on and off more frequently than a two-stage furnace of a variable-stage furnace. In addition, it also works harder when it is on, since it can only operate at full capacity. The result is excess wear and tear on a furnace over time, meaning more mechanical breakdowns and earlier equipment failure.

Zoning Compatibility

One of the best ways to save money on heating costs is to install a zoned HVAC system. This type of heating and cooling system is controlled by separate thermostats located in multiple rooms or areas of a home. Heat loads are reduced and little heated air is wasted with such a system, since the heat can be concentrated exclusively in the areas you occupy.

Unfortunately, a single-stage furnace cannot be adapted to fit with a zoned HVAC system. If you plan to go zoned you must install a variable-speed or two-stage furnace, which will allow such a system to function at maximum efficiency.

Reduced Energy Costs

With variable-speed or two-stage furnaces, less energy will be required to heat your home, and less money will be therefore be required to pay your energy bills.

It should be noted that single-stage furnaces cost less than two-stage furnaces, and a two-stage furnace will be less expensive than a variable-speed model. But the energy-efficient models will save you a lot more money on energy costs than a single-stage furnace, allowing you to recover the cost of your initial investment more quickly.

Consult the Furnace Experts at ABE Heating and Cooling

As a licensed Ruud dealer, we can introduce you to some of the most energy-efficient and cost-effective gas furnaces currently available on the market. ABE Heating and Cooling offers great products with iron-clad warranties and superior installation services, all at manageable prices suitable for any budget. We are located in Brighton, Colorado and serve the entire Denver Metro Area, and if you would like to learn more about high-efficiency furnaces please contact us today to discuss the possibilities.