Retrofitting Your Furnace Pilot Light

Do you know how energy efficient your furnace is? Most homeowners don't really know. A central heating furnace's efficiency is measured in terms of annual fuel utilization efficiency (AFUE). The U. S. Federal Trade Commission forces manufacturers of new furnaces or boilers to display their AFUE on their product so that consumers may compare heating efficiencies of various models.

AFUE expresses how efficient the appliance is in the energy in its fuel over the course of a typical year. To be more precise, AFUE is the ratio of heat output of the furnace compared to the total energy consumed by a furnace. An AFUE of 90% means that 90% of the energy in the fuel becomes heat for the home and the other 10% escapes up the chimney and elsewhere. AFUE doesn't include the heat losses of the duct system or piping, which can be as much as 35% of the energy for output of the furnace when ducts are located in the attic.

You can figure a system's efficiency not only by its AFUE but also by its equipment features and type. For example, older, low-efficiency heating systems have a continuous pilot light, heavy heat exchangers and an AFUE of around 68%-72%. Newer, high-efficiency heating systems feature condensing flue gases in a second heat exchanger for extra efficiency, and with sealed combustion chambers, attain 90%-97% AFUE.

Don't worry, you aren't stuck with old money-pit furnace forever. Furnaces can be retrofitted to raise their efficiency. Upgrades improve both the safety and efficiency of otherwise sound, older systems. The costs of retrofits should be carefully weighed against the cost of a new furnace, especially if replacement is likely within a few years or if you wish to switch to a different system for other reasons, like adding air conditioning or going all-gas from electric power.

Vintage model furnaces with a continuous pilot light can be retrofitted with intermittent ignition devices. These are difficult to install, however, and only should be installed by certified professionals. Costing about $250, they characteristically have a payback period of less than 10 years. Even though intermittent ignition devices can save you some in fuel costs, they are not always that cost effective when installed on old equipment. Turning off a furnace's pilot light in the spring and turning it back on again in the fall can usually save the same amount of money as you would with one of these devices. Not all continuous pilot light furnaces can accommodate this solution, though, so check with your furnace manual or heating contractor first.