That red tag dangling from your furnace isn't a holiday present -- it's a sign that your furnace is need of some serious attention. Once your HVAC technician leaves one of these behind, you won't be able to use your furnace until the underlying problem is safely corrected.

If your furnace was recently red-tagged, then don't panic. Here's an in-depth guide on the practice, including the reasons behind it and how you can safely get rid of your furnace's red tag.

Why Furnaces Get Red-Tagged

Your HVAC technician may red-tag your furnace if it can't be operated without putting yourself and others inside your home in danger. A red-tagged furnace can have one or more problems that prevent it from being used in a safe manner:

• Cracked heat exchangers - A cracked heat exchanger can vent dangerous levels of carbon monoxide into your home, turning an otherwise faulty furnace into a silent and deadly hazard.
• Blocked or damaged flue vents - Flue vent blockages can prevent exhaust gases from leaving the furnace and redirect them back into your home.
• Natural gas or fuel oil leak - Operating a furnace that's leaking fuel can have explosive results.
• Electrocution hazards - Faulty wiring or a malfunctioning heating element can pose an electrocution hazard for anyone attempting to operate the furnace.

Reputable HVAC technicians will only red-tag a furnace if it fails inspection for any of the above reasons. You won't have to worry about your furnace being red-tagged over a dirty air filter or any other relatively trivial maintenance issue.

What to Do About a Red-Tagged Furnace

The one thing you don't want to do to a red-tagged furnace is turn it on. Doing so could prove harmful or even deadly under the right circumstances. Instead, find out from your HVAC technician why your furnace was red-tagged. Once you have this knowledge, you can decide how to move forward.

Your HVAC technician will recommend scheduling repairs as soon as possible. In the meantime, you'll need an alternative source of heat to rely on. If you don't have a fireplace, you can always use one or two portable space heaters for temporary warmth.

If you're a renter, notify your landlord immediately so repairs can be scheduled. The sooner your landlord can arrange for a professional repair, the shorter your time will be without your main source of heat. Once your furnace is repaired, your heater repair technician may inspect the furnace again before giving it a clean bill of health.