While many heating systems start blowing cold air at the beginning of a cycle, it should only take a second for the temperature to change so that warm air flows out of your vents. If your heating system is blowing cold air there are a number of common issues you can check before calling the team at Sanborn’s for professional repair.

Our certified technicians train extensively to understand the complex heating systems within your home and will quickly identify the reason cold air instead of warm air is circulating through your home.

Basic Steps to Check When Air Vents Blow Cold Air

If you suspect your heating system is weakened or damaged, the best action is to immediately shut down the system. This includes any changes in the sound and smells of your heating system. Often the first sign of a potential breakdown is reduced performance. Sanborn’s has a list of things you should check in order to troubleshoot your home’s comfort issues.


Checking the function of the thermostat is the first step to troubleshooting any HVAC issue. Make sure your thermostat is not set to cooling mode. Someone adjusting the thermostat without permission or on accident happens all the time.

Power surges, age, and low batteries can all impact a thermostat. If applicable replace the batteries on your thermostat. In all cases, turn the thermostat off and on to see if this resolves the issue. Thermostats tend to last 10 years, and replacing yours can help restore comfort to your home.

Air Filter

Air filters are one of the simplest and most important parts of your HVAC system. Air filters should be checked each month and replaced frequently. A dirty air filter can disrupt airflow into the furnace. Pleated air filters may become clogged with dust, debris, and pet dander. Obstructed airflow will reduce efficiency, cause a weak air flow through vents and even choke components within furnaces and heat pumps.


Inspect air filters and return vents. Excessive dust on vents includes a dirty ventilation system. Clogged air ducts adversely affect heating systems. Closed vents and vents blocked by furniture and other obstructions also impact performance. When professional maintenance is performed air filters, vents and air ducts are inspected. If the system within your home has been neglected these components become dirty.

Furnaces Problems

A furnace blowing cold air can be caused by a number of internal issues. Anytime you detect any strange sound or odor from a gas furnace the system should be shut down.  There are a number of issues that are common when cold air blows from your furnace including:

Heat Exchanger

There are two primary components within a furnace: a heat exchanger and a blower. The blower motor and fan circulate air throughout your home. The heat exchanger uses coils to transfer heat from the ignited gas to the air. When cold air blows from a furnace the heat exchanger, furnace burner, or exhaust are likely the cause. This may be due to dirty components, broken parts, or the many safety mechanisms within the gas system.

Flame Detector

This is a safety device within your furnace. At the beginning of the combustion stage, the gas valve opens. Flame detectors are electrical sensors that detect the presence of a flame. If there is no flame, the sensor turns the system off. A faulty, damaged, or dirty flame sensor may also shut down your furnace.

Pilot Light

Modern furnaces typically detect issues with gas but a weak pilot light or faulty pilot lights may result in cold air blowing during heating cycles. Like other features within the gas delivery system, the entire furnace may shut down when the pilot light malfunctions.

Condensate Lines

Blocked and clogged condensate drain lines typically cause a furnace to shut down. High-efficiency furnaces produce water that either drains or pumps away from the furnace. If your furnace is not running and there is water beneath the furnace, this is a clue that your drain lines need to be cleaned.

Heat Pump

Heat pumps are quite popular because they are versatile delivery both cool air and warm air. If a heat pump is blowing cold air during the fall and winter, always check the thermostat and air filter first. Other issues unique to heat pumps that you can check for are:

Defrost Mode

The most common reason a heat pump is blowing cold air through your air vents is defrost mode. This is a safety feature to melt frost and ice within the system. During defrost mode your heat pump made switch modes to heat up the outdoor coils. Indoor temperatures will fall because the system is briefly in cooling mode. If your outdoor unit is covered in frost, allow the system to run. If the issue persists, dirt and other issues within the heat pump may need to be cleaned or repaired.

Reverse Valve

The reverse valve is how a heat pump changes modes from cooling to warming. A faulty reverse valve may cause a heat pump to stay in cooling mode. When this occurs the fan may still run even though your heat pump isn’t producing warm air.

When to Call Professional HVAC Technicians

Aside from checking air filters, cleaning drains, and resetting your thermostat, cold air blowing from your heating system is a warning of potential problems. Internal issues within a furnace or heat pumps often manifest as peculiar issues like cold air along with strange sounds. While all homeowners should understand how their heating system works and the likely causes of repair, calling professionals at Sanborn’s is always recommended.

When our team inspects and diagnoses the cause of your heating issues. The team at Sanborn’s provides complete heating, cooling, indoor air quality, and electrical services. We are happy to inspect all of your equipment to make sure hot air fills your home in the winter and cold air greets you all summer long. Contact us today to schedule an appointment.