Furnaces roar, rattle and hum as a matter of course, but some sounds are to be taken more seriously than others. A hissing noise, for example, suggests a leak somewhere in the system, but there are other possible explanations as well. Any sort of leak within a furnace can be dangerous and even deadly, so only begin internal inspections with the entire system shut off and cooled. If you are not confident about your ability to diagnose or fix the issue on your own, call a furnace repair specialist immediately to prevent any unnecessary damage to your furnace or yourself.
Detecting a Gas Leak
Whenever you hear a hissing sound coming from near your furnace, your first action should be to determine that it is not a gas leak. Natural gas intended for home use is treated with molecules to give it a foul odor. Approach the area where you hear the hissing slowly; if you begin to smell rotten eggs or a similarly unpleasant smell, you are likely dealing with a gas leak and should evacuate your home quickly before contacting professionals.
Ruling Out the Regulator
Regulators moderate the flow of gas through the pipes in your home and appliances, increasing and decreasing the pressure in the pipes as demand requires. When operating at full capacity, the rush of gas through this regulator can create a hissing noise. If the hissing sound occurs near a propane tank or is only really noticeable when the furnace first kicks on, you probably just have a loud regulator. It may still be wise, though, to have the area inspected for leaks.
Checking for Air Leaks
Not all leaks are as dangerous as natural gas leaks, but they can still cause you problems. As heating and cooling systems age, they begin to loosen around the seams, and air leaks can occur as a consequence. These leaks may be in your ducts, around the service panel or within the furnace itself. Tracking them down can be difficult without specialized leak detectors, and furnace repair contractors will be able to more effectively identify them and seal the leaks without needing to replace whole segments of ducting.
The good news is that in most cases, a hissing sound coming from your furnace system can be repaired or minimized without needing extensive renovations. You should, however, investigate these sounds quickly. Even if the leak is not pouring natural gas into your home, it may be reducing your heating efficiency by as much as 40 percent. If you cannot determine the source of the hissing or repair it on your own, spare yourself the aggravation and expense of inaction and call your local contractors as soon as possible to take care of the problem.