That subtle hissing from a constant-piloted gas furnace is continuously wasted energy. The same applies to constant-piloted gas water, pool and other heaters as well. Similarly, being vented into a chimney accentuates these losses by pulling heated air through these appliances.
They are certainly becoming fewer and further between — haven’t run into one in a couple of years, until this week again. Furnace looked good, having lived in a nice, dry cellar for many years. (Moisture is the nemesis of hot air furnace systems.) That hiss is even soothing to the neophyte, until the gas bill comes in.
In our experience the numbers are very compelling, considering the efficiency advances in “Condensing Gas” Appliances as to question the motives for their continuing existence. These 70% AFUE range “gas suckers” are being replaced by 95% AFUE range appliances. The last one we changed a few years ago netted a solid 45% annual fuel reduction. Combine this with the Tax Credit Incentives currently available and you have a sure bet!
Diss the Hiss!
Last Edit: 10/10/12 pdm