Why you should upgrade to an energy-efficient forced-air furnace
By Fran J. Donegan
If the Holy Grail of furnace manufacturers is to wring every last BTU of heat out of the fuel that feeds the products they make, they are pretty close. Thanks to a combination of government regulations, the need to conserve energy and some pretty innovative technology, you can buy forced-air furnaces that are over 98% energy-efficient.
How Efficiency is Measured
Furnaces are rated by their annual fuel utilization efficiency (AFUE). The rating reflects the percentage of fuel that is turned into heat. A higher rating means more of your energy dollar is providing heat and comfort to your home, rather than going up the flue as wasted energy.
Models that have a 98% AFUE are at the top of the heap for forced-air furnaces fueled by natural gas, propane or fuel oil. But don't confuse these with electric furnaces that have a 95% to 100% AFUE. As a fuel source, electricity is much more expensive than oil or natural gas, and electric furnaces rarely make economic sense. Most electric furnaces are used in homes located in areas with very mild climates.
Not all new furnaces offer a super-high AFUE rating. In fact, furnaces can be divided into three broad categories:
- Low-Efficiency Systems. These are furnaces that are fairly old and have been in place for some time. It is safe to assume that the older the furnace, the less efficient it is—some systems provide as low as a 60% AFUE. These heating systems are normally outdated, and can waste energy and money.
- Mid-Efficiency Systems. These furnaces have an AFUE percentage anywhere in the 80s. The minimum standard AFUE percentage today is 80%.
- High- Efficiency Systems. These include any furnace with a rating above 90% AFUE.
Advances in Technology
Mid-efficiency systems differ from older models in that they tend to be smaller and lighter, which reduces wasted energy caused by the furnace cycling on and off. They are also better at controlling combustion gases and combustion air, and they rely on electronic ignition rather than standing pilot lights.
High-efficiency systems take technology even further by using sealed combustion, which means the furnace draws air for combustion from outside rather than relying on the air inside the home. Having a variable speed motor means the system is not always running at full throttle. They can also run at a slower speed, when applicable, to save energy. Multi-stage gas valves do a more efficient job of regulating heat output than single-stage valves. They also have a second heat exchanger that draws energy from what would normally be exhaust gases. The only thing left behind is water that condenses from the gas, which is pumped away. The heat exchangers on these models are usually made of stainless steel to protect against corrosion.
A mid-efficiency furnace starts at around $1,700, while a high-efficiency model starts at about $2,500. The finished cost of the project can go up from there based on any additional changes that need to be made to your heating system.
Are They Worth the Price?
You should replace your existing furnace if it’s more than 15 years old, if there are cold spots in your home, or if your furnace has a history of needing major repairs. If you’re paying higher energy bills than usual, you should also consider replacement. Although there could be another reason for your high bills, including leaky ducts or a lack of insulation and weather sealing, it could mean that the current furnace system is not the right size for the house. A new, properly sized system would solve that problem.
If you live in a cold climate, it makes sense to consider a high-efficiency unit. It will cost more upfront, but you will save on future energy bills. For warm climates, where air-conditioning is the major energy cost, a mid-efficiency unit may make more sense. In either case, remember that the furnace is one component of a multi-pronged energy strategy. If your goal is to reduce energy usage and shrink your carbon footprint, placing a high-efficiency furnace in a house that is under-insulated and not weather-sealed does not make much sense.
When it’s time to install the new furnace, be wary of an HVAC contractor who wants to replace your existing furnace with a same-size unit without doing an energy assessment of the house. The assessment will help you get the correct size system for your home. The contractor or dealer can also calculate what your energy savings will be with the new system.
Fran Donegan is a home improvement writer from New Jersey who provides tips to homeowners on heating systems and other house infrastructure for The Home Depot. Fran has also written the DIY homeowner books Pools and Spas and Paint Your Home. You can review furnaces available at Home Depot online here.
Companies: The Home Depot
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