What Makes High-Efficiency Condensing Furnaces So Energy Efficient?

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Suppose you’re serious about saving energy but don’t want to sacrifice indoor comfort. In that case, high-efficiency condensing furnaces offer a significant upgrade path. Condensing furnaces regularly achieve high Annual Fuel Utilization Efficiency (AFUE) ratings, with some furnaces rated at 98 percent or more. In comparison, the average conventional furnace is typically rated at an AFUE of 80 percent.

There’s more than meets the eye when it comes to condensing furnaces and the impressive efficiency they offer. The following provides an in-depth look at the components that make the condensing furnace tick and how they save you energy.

Electronic Ignition

Many older furnaces rely on a conventional pilot light for the startup. Pilot lights must remain on at all times, meaning your furnace constantly consumes a small amount of fuel to keep the pilot lit. This fuel usage can add up over months, resulting in higher long-term utility costs.

Condensing furnaces do away with pilot lights in favor of electronic ignition. In addition to eliminating wasted fuel, electronic ignition systems offer better reliability than standing pilot systems.

Modulating Burner Gas Valve

Burner gas valves are another area where the condensing furnace stands out from its traditional brethren. The average conventional furnace uses a burner gas valve with two states: on and off. This means that single-stage burner gas valves operate at 100 percent when activated. Unfortunately, single-stage burner gas valves are impractical when it comes to moderating the burner flame for improved energy efficiency.

Some furnaces get around the inefficiency of single-stage burner gas valves by offering dual-stage versions instead. Dual-stage burner gas valves provide high and low settings via electronic controls. These controls give dual-stage burner gas valves a greater level of flexibility than their single-stage counterparts.

Modulating burner gas valves offer an even greater range of condensing furnaces. In addition, these gas valves can increase or decrease their output in single-percent increments. Such fine-tuned control helps eliminate drastic temperature swings while boosting the furnace’s overall efficiency.

Variable-Speed Blower Motor

Ever notice how most conventional furnaces seem to run at full blast? That’s because traditional furnaces rely on permanent split capacitor (PSC) blower motors for air circulation. While these motors are simple, inexpensive, and robust, they’re also rated at a single operating speed.

The lack of variable controls makes it nearly impossible to moderate indoor temperatures on conventional furnaces without the blower motor stopping and starting repeatedly.

This is where the electronically commutating motor or ECM comes into play. Unlike PSC motors, ECMs can operate at various speeds without any penalties in energy efficiency. In addition, whereas conventional motors have no choice but to run at full blast, variable-speed blower motors can adjust their speeds in response to heating demands.

Variable-speed blower motors help condensing furnaces achieve efficient and highly versatile home comfort. For example, these motors can operate at extremely low RPMs to provide quiet, continuous air circulation throughout each room of your home.

Sealed Combustion Chamber

Conventional furnaces often use atmospheric combustion chambers that draw their air from indoor spaces. However, the need for an indoor air supply leaves the combustion chamber exposed to the rest of the home. In addition, such a design leaves the furnace vulnerable to backdraft, where combustion gases are drawn out of the exhaust flue under negative pressure and back into the home.

In contrast, condensing furnaces use sealed combustion chambers entirely separate from indoor spaces. Instead, the combustion chamber receives its air supply from the outdoors. As a result, sealed combustion chambers are safer and more efficient since minimal heat is lost to the furnace’s immediate surroundings.

Secondary Heat Exchanger

On a conventional furnace, the hot exhaust gases generated through the combustion process travel through the heat exchanger. This series of metal tubes pass the heat between the passing exhaust gases and the circulating air that flows over the device. Any excess heat is carried away into the flue and vented outdoors.

Condensing furnaces prevent excess heat from being wasted by circulating exhaust gases through another heat exchanger. The secondary heat exchanger scavenges waste heat from the passing exhaust, boosting the furnace’s efficiency. This process also cools the exhaust gases to the point where they can pass harmlessly through PVC pipes.

Heat Recovery Ventilator

Some condensing furnaces come equipped with a heat recovery ventilator. This device not only pulls fresh outdoor air into the furnace but also pulls heat from stale indoor air via a built-in air-to-air heat exchanger. The extracted heat is then used to pre-heat the incoming air before reaching the furnace.

HRVs are often necessary for tightly sealed homes since there aren’t any cracks or crevices that fresh outdoor air can be pulled through. Using an HRV also improves a condensing furnace’s overall energy efficiency.

Now that you know what makes condensing furnaces so energy efficient, give the experts at Derek Sawyer’s Heating & Air Conditioning a call and schedule your next heating system installation today.

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