See no evil, hear no evil, smell no evil. Sometimes your senses will tell you that your heating system is feeling under the weather, even if you're staying comfortable. There are some weird signs a heating system may exhibit when it needs attention right away.
Symptom 1) Signs of leakage around the furnace.
You should never see any drainage, or anything wet around your furnace. Sometimes the culprit is an overhead pipe or drain that's leaking. It should be fixed immediately to avoid corroding or otherwise damaging your furnace.
If your furnace is a newer one, with a PVC pipe draining condensate, chances are it's a high-efficiency unit. There's probably a leak in the drainage pipes somewhere that must be repaired.
There are a variety of other problems that can cause leaks around a furnace. For example, a secondary heat exchanger or humidifier may be broken. There may be a leak from an AC unit. If you can't locate and seal the leak, it's time to call a heater repair professional.
Symptom 2) Hissing noises you've never heard before.
Some furnaces or registers will make hissing noises normally. If you smell gas and hear hissing, check that you do not have a dangerous fuel leak. If you notice a new, distinct hissing sound when the furnace fan is running, and it's not a propane or gas leak, it could be the sign of a tear or separation of duct work.
Some duct work is too large or too small for a home's needs. It may not last as long under the pressure of delivering hot and cold air. Animals can be very destructive to duct work. Flooding, earthquakes and high winds can cause duct work to break or tear.
When forced air escapes from leaky duct work, your furnace or AC unit must work that much harder to keep your home comfortable. Have ducts inspected once a year and sealed where necessary. You can have the ducts cleaned at the same time.
Symptom 3) A new burning smell from the furnace.
If your furnace has been running for at least a week or so with no smells and then starts stinking, something may be seriously wrong. If you suddenly notice a burning rubber or metal smell, or if there's smoke present, as if the furnace is catching on fire, turn it off. Leave the home if necessary, calling for help from your local fire and rescue if you fear the home may catch on fire.
Hopefully things won't be that dramatic. The blower motor may be broken or malfunctioning, causing heat to build up in the furnace. If you suspect the blower is broken, you can try to troubleshoot it yourself. But the furnace cannot work without the blower, so contact a heating repair specialist if you need a new one. You can have your HVAC system tuned up when the new blower is installed.
The electricity or fuel needed to heat your home is the largest part of your energy costs. Keeping your heater in top repair increases its efficiency and saves you money. Watch for any symptoms that indicate your HVAC system needs a checkup.