What every best Furnaces has:
- The proper AFUE rating.
- Two stage valves.
- A programmable thermostat.
If you live in a milder climate, experts say you should consider a less efficient (and less expensive) 80 percent AFUE furnace. Although condensing furnaces, which range from 90 to 97 percent AFUE, waste less heat, experts say it might be overkill for homes that are considered high-performance (that is, very energy efficient) or that are located where winters are milder. In fact, some HVAC experts say an 80 percent AFUE furnace is more efficient if it's the proper size for the home, as opposed to a possibly oversized 90 percent condenser furnace.
Additionally, if you're replacing an older furnace that's rated from 56 percent to 70 percent AFUE, the upgrade to an 80 percent AFUE model should cut your fuel bills significantly, although the break-even period will depend on your gas rates and how they change over time. Federal regulations that went into effect in May 2013, and others that took effect in January 2015, require that all new gas furnace installations have a minimum AFUE of 80 percent for non-weatherized gas furnaces, 81 percent for weatherized gas furnaces. If you live in one of 30 Northern states with particularly harsh winters, that point is moot -- new installations and upgrades there are required to meet a minimum AFUE level of 90 percent.
Gas furnaces with an AFUE rating of 80 percent cost less initially, and are less expensive to install -- perhaps half as much compared to high efficiency condensing furnaces. However, if you are especially concerned about pollution, you may prefer a more efficient condensing furnace, which will produce lower carbon dioxide emissions than an 80 percent AFUE furnace.