The last thing anyone wants in the dead of winter is a cold draft from their home's HVAC vents. When your furnace kicks on, you shouldn't feel anything except comfortable, warm air blowing through your home. If you're noticing lukewarm or even cold air from your vents, that's a good indication that something might be wrong with your heating system.

Luckily, not every problem with a furnace is as severe as a cracked heat exchanger, and you aren't necessarily in for an eye-watering repair bill. If you've just started to notice colder-than-normal air, it may be due to one of these three relatively minor problems.

1. Incorrect Fan Settings

Before condemning your furnace and making a potentially costly HVAC call, you should at least check for user error. Most thermostats should have four fan modes: auto, on, circulate, and off. Out of these modes, "auto" is the only one that guarantees you'll get hot air whenever the blower is working. Both "on" and "circulate" can potentially distribute ice-cold air throughout your entire home.

Since checking your thermostats costs nothing and only takes a few minutes, this should always be your first step when diagnosing any problem.

2. Bad Limit Switch

Your furnace's limit switch is a safety feature that protects the heat exchanger from severe damage. The heat exchanger contains exhaust fumes from your furnace's combustion, and overheating this part can cause it to crack. If the area near your heat exchanger gets too warm, the limit switch will trip and shut down the burners.

When this happens, your house blower may not switch off. Since your burners aren't running, the blower will continue to push cold air around your home. A faulty switch can produce similar symptoms. However, it's always a good idea to have a professional examine and replace this part to confirm that you aren't suffering from an actual overheating issue.

3. Bad Igniter

Most furnaces engage the blower motor within about a minute of the igniter coming on. While your furnace should have safety switches to prove ignition, the blower may still turn on even if the furnace does not ignite. If your ignition element is dirty or faulty, you may have all the conditions necessary for combustion, but your fuel will never light up, and you won't get any heat.

While the igniter is another component you'll want a professional to check, you can still observe if your furnace isn't lighting. If you're comfortable removing the panel on your furnace, you can watch as it goes through its start-up sequence. At some point, the electric igniter should begin to glow. If it doesn't, you may have a faulty igniter that's preventing your furnace from keeping your home cozy and toasty.

Contact an HVAC repair service if your home is experiencing any of these issues.