Understanding Different Types of Gas Furnaces: 80 vs 90 Efficiency

Choosing the right type of gas furnace can seem like a daunting task, especially when you start looking into efficiency ratings and the various options available. In this article, we will explore the differences between 80 efficiency furnaces and 90 efficiency furnaces, along with an overview of other types of gas furnaces, to help you make an informed decision.

What is Gas Furnace Efficiency?

Gas furnace efficiency is typically measured by the Annual Fuel Utilization Efficiency (AFUE), which indicates the percentage of heat generated by the furnace that reaches your home. Higher AFUE ratings indicate more energy efficiency and cost savings over time for homeowners.

Efficiency Ratings Explained

There are essentially three types of AFUE categories for gas furnaces:

Low Efficiency: 55 to 72 – These furnaces are considered historical and obsolete, with chimney exhaust temperatures at around 700°F. Mid Efficiency: 78 to 82 – Chimney exhaust temperatures are around 400°F, and these are generally referred to as Standard or Conventional furnaces. High Efficiency: 90 – These furnaces have an AFUE that can reach up to 98.5, and they are known as Condensing furnaces, with exhaust temperatures around 100°F.

Understanding these categories will help you determine the type of furnace that fits your specific needs and budget.

Differences between 80 and 90 Efficiency Furnaces

The primary difference between an 80 efficiency furnace and a 90 efficiency furnace lies in how they handle heat recovery and exhaust temperature. The higher the efficiency, the better they are at recovering heat and wasting less energy, ultimately leading to greater cost savings in the long run.

The 80 efficiency furnace operates in an open combustion process, where it draws air from the surrounding area to generate heat. This means that it has a higher level of heat loss due to the unsealed combustion chamber. On the other hand, the 90 efficiency furnace uses sealed combustion, pulling air from the outside to create heat, which results in a lower exhaust temperature.

Because 90 efficiency furnaces have a lower exhaust temperature, they often require a plastic chimney, condensate drain, and special installation requirements. These features are not necessary for an 80 efficiency furnace. Additionally, the byproducts of combustion in a 90 efficiency furnace are more corrosive, and some municipalities prohibit the discharge of this condensate into sewage systems.

Installation Considerations

When considering installing a high-efficiency furnace, several factors need to be taken into account:

Chimney and Venting System: High-efficiency furnaces often require a different type of venting system, such as a plastic pipe, while 80 efficiency furnaces can use a traditional metal chimney. This adds an additional cost and complexity to the installation process. Additional Intake Vent: Depending on the installation location, high-efficiency furnaces may require an additional intake vent to bring outside air to the sealed combustion chamber. This is crucial for proper operation and safety. Condensate Management: Condensing furnaces produce a significant amount of condensate, which needs to be properly managed. Most require a condensate pump to handle the water that forms due to the condensation of exhaust gases.

Conclusion

Choosing between an 80 efficiency and a 90 efficiency furnace depends on your specific needs and budget. While an 80 efficiency furnace may be less expensive initially, the long-term cost savings from a high-efficiency option can offset the higher upfront costs. It's essential to consult with a professional HVAC contractor to ensure proper installation and maintenance of your chosen furnace.

Key Takeaways

80 efficiency furnaces use open combustion, while 90 efficiency furnaces use sealed combustion. 90 efficiency furnaces require specialized venting, intake vents, and condensate management systems. High-efficiency systems are more expensive but offer greater long-term cost savings.