Calculating a furnace’s energy costs requires considering both the gas it burns and the electricity it consumes to run its blowers and controls.
How efficiently a furnace convert’s gas into heating energy is reflected in its (AFUE) annual fuel utilization efficiency rating, which is measured as a percentage. The higher that percentage, the more heat the furnace can provide.
Today, the most efficient models have an AFUE of about 96% and the lowest efficiency allowed by law for new gas furnaces is 78%.
THE BEST CHOICES
All offer furnaces in a range of capacities and efficiencies. Manufacturers generally deliver on those specifications. All brands possess basically similar features. The most important steps in selecting a furnace are to ensure that the unit’s specifications meet your expectations
HOW BIG A FURNACE?
When it comes to furnaces, size matters. A small furnace will not keep the house comfortable during extreme cold weather. A large furnace will cycle on and off more often. That causes wear and tear on its components, wastes energy, and may cause uncomfortable temperature. Also, upgrading to a larger furnace may require the installation of bigger ducts to accommodate the increased airflow. In wrong size ducts the airflow can be noisy.
What makes a furnace better?
Variable speed blowers. They can deliver air more slowly (and more quietly) when less heat is needed. Heat can then be delivered more continuously, with fewer drafts or uncomfortable changes in temperature and airflow.
Ignition systems. Few furnaces have a pilot light, a flame that burns continuously, awaiting the next command to ignite the burners. More common are furnaces with direct spark or hot-surface ignition. That increases efficiency and is often reflected in the furnaces’ high AFUE rating. (AFUE stands for annual fuel-utilization efficiency.)
Dual heat exchanger. Heat exchangers are the components that draw heat from the burned gas. To draw more heat from the air they burn, energy-efficient furnaces supplement the primary exchanger with a second exchanger.
Venting and repairs
When you are purchasing a new furnace, you might also need to consider your home’s vents and chimneys. Replacing a low-efficiency furnace with a 90% or more efficiency requires installing a vent that meets the special needs of a high-efficiency furnace. If other appliances (water heater) share a vent or chimney with the old furnace, they also may need new or modified venting.