Often when you hear about combustion furnace options, fuel efficiency is the main metric thrown around.These are usually shown in terms of AFUE (annualized fuel utilization efficiency) percentage, in other words, the amount of fuel that gets converted into heat (furnaces with AFUE 90 percent and above are considered "high-efficiency"). High efficiency in a furnace is mainly accomplished with variable gas-valve staging and blower-motor speed. Modulating furnaces are considered the best in terms of both efficiency and performance.
Single-Stage Furnace Operation
To understand the benefits of modulating furnaces, it helps to realize that furnaces without multi-stage, variable-speed operation come with just one stage and one speed – meaning the gas valve is either open or closed, and the blower motor operates at 100 percent speed or not at all. When the thermostat signals the furnace to kick on, it immediately begins churning out heat at full blast, runs until the desired temperature is achieved, then shuts off.The result is short-cycling, especially during milder weather, with the furnace alternating between full-blast and "off" at relatively short intervals. Not only does full-go operation use more fuel than necessary to heat a house, the most fuel is consumed at start-up, so frequent on-and-off cycling also wastes energy.Short-cycling in a single-stage furnace without variable-speed operation also can result in uneven heating, as well as noticeable temperature swings.
Two-Stage and Modulating Furnaces
A two-stage furnace, with a gas valve that can open partially when it's not fully open, is a big improvement over a single-stage furnace. Even better is a modulating furnace featuring a gas valve with multiple staging, with the heating needs at any given time determining the setting. Two-stage or modulating operation is generally combined with a variable-speed blower motor, which also adapts its running speed depending on heating needs.These furnaces typically ramp up to full blast upon starting, then settle into lower-stage, lower-speed continuous operation, which results in more consistent temperatures throughout the house and less fuel consumption.
To discuss installing a new high-efficiency modulating furnace in your Broken Arrow area home, please contact us at Air Assurance.
Our goal is to help educate our customers in the Tulsa and Broken Arrow, Oklahoma area about energy and home comfort issues (specific to HVAC systems). For more information about modulating furnaces and other HVAC topics, call us at 918-217-8273.