furnace performance and rating

The performance of a furnace doesn't depend only on its energy efficiency rating, that is, its AFUE (Annual Fuel Utilization Efficiency) coefficient. Much more than other heating and cooling systems, its performance is also largely dependent on the quality of its installation.

When assessing the efficiency of a furnace, do not overestimate the opinions of contractors. Though important, they are typically biased. They tend to promote the brands that they know best or those that are most profitable to them...

Energy efficiency, AFUE and ratings

The Energy Star Label for furnaces includes their AFUE First of all, when selecting a furnace, consider its AFUE – that is, its energy efficiency rating or Annual Fuel Utilization Efficiency. The AFUE of a furnace is denoted in a percentage that expresses how much gas, oil or other energy source is converted into heat: say, 80%, 90%, 97%... A furnace with an AFUE of 80% only converts 80% of the fuel into heat. The other 20% is lost out...

Obviously, a more efficient furnace can easily pay off itself on the medium or long run with energy savings... It's easy to do the maths.

You can find the AFUE of a furnace in the rating labels of organizations like the Energy Star, the ACEEE or the AHRI (Air-Conditioning, Heating, and Refrigeration Institute)).

Note:
Outside North America - where furnaces are much less common on the household segment - furnace rating and certification may not exist.

performance Hints

To ensure a good performance, choose a good furnace brand and a company long in the business. It's too risky to choose a furnace from a new and unknown manufacturer.

Pay also attention to some quality hints, like the heat exchanger warranty. If a manufacturers is willing to back the heat exchanger of its furnace (its most expensive part) for 20 years or so, that's an obviously good sign of quality and performance.

The Furnace efficiency and the fuel issue

The fuel issue may also count when assessing the efficiency of a furnace. Though marginally, the gas furnaces are more efficient and clean and easy to maintain than oil furnaces. But there are also the wood pellet furnaces option, for those valuing the running costs the and environmental side of the furnace performance.

See:
Gas vs. Oil furnaces
Direct-Vent Ductless Gas Furnaces
Wood Pellet Furnaces

the furnace Installation

But most of all, do not forget the extreme importance of furnace installation in their performance. The installation is expensive - often more costly than the furnace - and at least as important as the furnace in itself. An energy efficient furnace with a poor installation can be outperformed by units with lower AFUEs but better installed.

The venting, the duct system, the sizing, and several other details are crucial for the whole performance of a furnace system.

So, pay special attention to the contractor issue. The furnace manufacturer may help you to find out a certified contractor. Or you may look for certified installers at NATE (North American Technician Excellence), HVAC Excellence, Smacna or through the Resnet Qualified Contractor tool.