Your furnace is the warm heart of your home, keeping it toasty through the fall and winter. The last thing you expect when you turn your heater on is a blast of chilly air. The top reasons for a furnace blowing cold air include thermostat problems, clogged air filters or duct issues.

Top 10 Reasons for a Furnace Blowing Cold

Let’s explore 10 common causes of a heater blowing cold.

1. Thermostat Problems

Often, the thermostat is the reason why cold air comes from your heater. There are a few things to check:

• Incorrect setting: The fan blows cold air once the furnace reaches optimal temperature. Changing the thermostat to “auto” rather than “fan” prevents this. You may find the thermostat still set on “cool.” Adjusting to “heat” could solve your cold air problem. One final trick is checking the temperature and raising it several degrees. It might be on air conditioner mode or someone may have altered the temperature.
• Low battery: When its batteries lose power, so does your thermostat. You should replace thermostat batteries at least once a year.

2. Compromised Air Filter

The air filter prevents debris from getting into the heating system and ducts. A furnace heats and circulates air, but a clogged filter limits airflow to the heat exchanger. Limit switches control airflow and temperature inside the furnace. Reduced air causes the burners to turn off, so cool air blows instead of hot air.

Regular filter cleaning prevents blockage. Depending on use, you may need to replace your air filters every three months. Schedule an annual HVAC service to avoid damage from compromised filters.

3. Leaky or Damaged Ducts

Ductwork issues could be responsible for heating system inefficiencies. There are two main causes:

• Leaky ducts: Holes in ductwork account for 20% of reduced heating efficiency. Cold air can enter ducts through gaps or holes and come out of vents. Old or damaged ducts may be the culprit for warm air leaking out and cold air getting in.
• Duct size: If ducts are too small, it restricts airflow to the furnace.

Correcting ductwork problems is best left to the professionals. Improper sealing or installation through DIY can cause bigger problems in the future.

4. Gas Supply Issue

A gas furnace needs fuel to function. If the line is faulty or the gas has run out, the furnace won’t receive the supply it needs to heat. A lack of gas would also affect your gas stove and water heater.

Check whether the gas needs topping up. For more significant issues, such as a leaking or bent gas line, consult an HVAC repair company.

5. Blocked Air Vents

Closed in unused rooms or blocked by furniture can cause the furnace to malfunction. One or two closed vents have little impact, but multiple can cause improper heating. Unblocking or opening vents may give your furnace much-needed airflow.

6. Pilot Light Is Out

This issue applies to gas furnaces. When you turn on your furnace, the pilot light ignites the incoming gas. Electrical furnaces use electricity rather than a pilot light. Check that the pilot light is on. If not, try to reignite the pilot switch by following these steps:

1. Locate the pilot light assembly and reset switch. This is usually at the bottom of the furnace, but you can also find it in the manual.
2. Turn the reset switch to “off” to stop the gas flow.
3. Wait a few moments for the gas to dissipate.
4. Turn the toggle back to “pilot” to allow the gas to flow.
5. Push in the reset button and ignite the flame with a match or lighter. Once the flame burns without flickering, let go of the reset switch.

If the pilot light goes out, there may be a draft in the surrounding area. Alternatively, there may be a blockage in the pilot light supply valve. The components may also be dirty, damaged or faulty. Consult with a professional HVAC technician for a faulty pilot light.

7. Dirty Flame Sensor

The flame sensor detects there is flame and gas inside your furnace. This is an important safety feature, ensuring the gas valve opens only when the flame is burning. If the flame goes out, the flame sensor shuts off the gas.

Dirty or damaged sensors can’t detect the flame. This can result in the system shutting down or the blower may continue to run without a flame.

8. Control Panel Glitch

Modern furnaces regulate temperature through a control panel. Like any technology, glitches may occur that affect heating system operation. Should this happen, resetting the panel from the main power switch does the trick.

Check the furnace manual if you’re unsure where the main power switch is. Flick the switch off, wait a few minutes, and switch it on again. This resets the furnace controls.

9. Clogged Condensation Drain Line

Hot and cold air mixing causes condensation. A furnace’s condensation line feeds buildup down a pipe to a drainage point. If the pipe becomes blocked, moisture can affect the heating sensors.

A clogged drain line requires professional help. Contact a reputable HVAC service company to unblock the line.

10. Furnace Needs Time to Heat up

It may seem obvious, but heaters need some time to warm up. When you turn on a gas furnace, the flame ignites and the blower kicks in a few moments later. If you haven’t used the heating system in a while, the pipes have cold air they need to expel. Your heater may seem to be blowing cold, but the heating cycle might take a few minutes to start.

However, it could be time to call an HVAC technician if your furnace continues blowing cold air.

How to Prevent Furnace Problems

With a few tips, you can keep your furnace in top condition for those cold central PA winters!

Schedule Regular Maintenance

Regular maintenance ensures that your heater works when you need it most. Getting regular inspections and cleaning avoids costly repairs down the line. Benefits of a well-maintained furnace include:

• Reduced energy bills: A well-maintained heating system uses less energy. Better energy efficiency translates into lower utility bills.
• Increased safety: Frequent inspections identify any threats, such as gas leaks.
• Optimized performance: Replacing air filters, unclogging pipes and replacing worn components boosts performance.
• Prevents bigger problems: An experienced technician can catch minor problems before they escalate. Preventive maintenance saves you money on expensive repairs.

Use a Professional HVAC Technician

It can be tempting to tackle heating maintenance and repairs yourself, but it can cost more in the long run. Instead, trust experienced HVAC technicians, like the team at Leggett Inc. They have the right equipment and knowledge to complete the job right the first time.

Trust Leggett Inc. for Furnace Repair and Maintenance

Your furnace is an important part of your home’s HVAC system, keeping you warm during the cold season. Leggett has provided central PA homes with a full suite of HVAC services for over 50 years. Trust our skilled technicians to repair and maintain your furnace. Call us at 717-773-4562 or contact us online for a free quote.