Therefore, your furnace blowing cold air could result from a clogged or dirty air filter. If you have a dirty or clogged furnace filter, the cool air from inside your home will struggle to travel through it and into the furnace. This means you have insufficient air to heat and redistribute.
A furnace blowing cold air could be the result of a leak in your ducting. Over time, the changing temperatures wear on all sorts of things, including your ductwork. In fact, it's rather normal for ductwork to develop leaks over time. When ductwork has a leak, cold air will enter a duct and blow into your home.
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.
You shouldn't turn off your furnace just set the thermostat so the furnace will only come on if the temperature drops around 50F 10Celsius. On thermostats that run both the heater and AC, make sure the system is switched over to ``cool'' and the furnace won't turn on.
It May Be Blowing Relatively Cooler Air
Given that the ideal thermostat setting is at 68 degrees, blown air at 90 degrees is actually warmer than what is needed for heating. However, it is cooler compared to the average body temperature of 98.6 degrees, which makes it feel cool, and is often mistaken for cold air.
Common Reasons For Furnaces Blowing Cold Air:
Your Furnace Isn't Warmed Up Yet. Your Thermostat is Set Incorrectly. The Furnace Filter is Dirty. Your Furnace Has Overheated.
When we blow air from our mouth, if it reaches to an object fast, then a lot of ambient air gets mixed with it. The result is that the air falling on the object gets cold. Conversely, if the air from our mouth reaches the object slowly, it remains warm.
The issue could be as simple as an incorrectly set thermostat, so always double check the settings. A more serious problem is a miscalibrated thermostat (it's sensing the wrong temperatures and shutting the furnace off early) or one that has a bad connection to the control board in the HVAC system.
Problem 1: Incorrect thermostat settings The most common reason for a furnace fan that won't shut off or a furnace blowing cold air and won't shut off is the wrong thermostat settings. The solution: Check the thermostat settings. The fan setting should be on AUTO. If it's set to ON, the furnace fan won't shut off.
While furnaces can stop operating for complicated reasons, home owners should check a few usual suspects first behind a lack of hot blowing air: Electrical problems causing a loss of power. Blocked air vents and ducts restricting airflow. Improperly configured thermostat settings.
Check Furnace Air Filter
A dirty air filter hinders air movement through the furnace. This raises temperatures inside the furnace, and the limit switch shuts heating cycles down if the unit becomes too hot. If you have a dirty filter, replacing the filter typically stops cold air from blowing.
Check the thermostat
Maybe your heater is not blowing hot air even though the fan is running. As a result, any air that blows out of the vents while your heater is off will usually feel cold. In such a case, there could be an easy solution, particularly if your thermostat setting is the problem.
Choose "AUTO" for energy savings and "ON" if you want constant air circulation or improved air filtration. Temperatures can soar or plummet depending on the time of year. Throughout the year, it is important to have reliable heating and cooling systems in order to keep your home supplied with cool or warm air.
Your furnace will blow cold air if there is no air to heat and send back into your home. Another reason you may not be getting enough air flow is if your ductwork is not sized properly. Unfortunately, this is quite common. If your return ductwork is too small, it will not be able to take in the required amount of air.
Hot air leaving the furnace burner is generally between 140 and 170 degrees Fahrenheit. By the time the airflow passes through the ductwork and enters a room at the supply vent, the temperature has typically dropped to about 120 to 140 degrees.
Furnace is not producing enough heat.
This may be caused by obstructed airflow or dirty or misaligned gas burners. In some cases, airflow is obstructed by a dirty furnace air filter, and if it is replaced, the problem is solved.
If you're cold even though your thermostat indicates you shouldn't be, your furnace likely isn't the problem. In most cases, it's working just fine. It's your home that needs attention. Lack of insulation, severe air leakage, and/or unbalanced ductwork are frequently to blame.
Check all the vents in your home and make sure they are fully open and unobstructed in the rooms you want heated. If they are blocked or covered with large furniture like couches or beds, the heat will be absorbed into upholstery, leaving the rooms cold.
Leaky Air Ducts
Your heater might also be blowing cold air because of leaky ducts. Leaks in your ductwork can cause warm air to escape before it reaches your rooms, causing cool air to come through the vents. A leak can occur because of poor insulation, aging ducts, or damage.
If the air feels chilly, start by checking your thermostat settings. Otherwise, you might need to replace your air filter or reignite your pilot light. Don't hesitate to call an HVAC expert if you can't identify or solve the problem.
Short Answer. The breath feels warm when blown out of an open mouth because the air is moving slower and can't remove heat from surfaces effectively, whereas it feels cold when blown through a smaller opening due to increased air speed which leads to more effective heat removal from surfaces.