How hot should air be coming out of furnace?

Author: Robert Klein  |  Last update: Thursday, October 30, 2025

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.

Why is my furnace blowing out lukewarm air?

The lukewarm air appearing in your heater can be the outcome of a leaky duct. If your air ducts are leaking, cool outside air is making its way into your ductwork. This can cause the air to really feel only lukewarm.

How hot should my furnace exhaust be?

The temperature is typically at or below 140 degrees. Due to the low exhaust temps, the exhaust byproducts will condense inside the vent pipe. The exhaust will condense and run back towards the furnace drain system, so a proper drain is necessary.

How warm should air be from a vent?

Ideally, there should be a temperature differential of around 14° to 20° Fahrenheit between the incoming air and the air being blown out by your air conditioner. This means that if the air entering the system is 75°F, the air coming out of the vent should be between 55°F and 61°F.

What should furnace supply air temperature be?

1 Answer. 50°C (122 F) is not unusual (as an initial default value) for zone heating supply air (especially for older designs), although 30°C to 35°C (~90F) is preferable.

What should the duct temp be

How hot should the air be coming out of my furnace?

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.

What should supply air temp be?

Well, the general consensus is somewhere between 14 to 20 degrees colder than the intake temperature. From my example, 55 to 61 degrees would be an acceptable range.

Why is my furnace air not hot enough?

A dirty furnace filter is one of the most common reasons furnaces don't produce enough heat. Luckily, this is an easy and inexpensive fix. While you're at it, buy one or two extras and make a note in your calendar to check it again in a month.

How hot should furnace ducts be?

A gas furnace typically operates at temperatures between 140-170 degrees, while a high-efficiency furnace operates around 110-140.

How much air should be coming out of my vents?

They can come out and test your equipment to determine how strong the airflow is. How strong should air come out of vents? The recommended airflow for each room is typically 50 cubic feet per minute. Let's take a look below at what this all means.

How do I know if my furnace is venting properly?

#1 Moisture and Condensation

Increased moisture within the home is a sign that your furnace venting isn't adequate. Without proper ventilation, fumes from the furnace leak into your home and cause condensation. This moisture is most notable in the morning and when you first turn on your heating unit.

Should furnace vents be hot to the touch?

Vents Feel Hot: Your furnace might feel warm to the touch, but your vents should not. Hot vents indicate improper venting.

How hot is flue gas in furnace?

The flue gas exit temperature is 750 °C after air preheater. Air is preheated from ambient temperature of 40 °C to 190 °C through an air pre-heater.

Why is the air coming out of my vents not hot?

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.

What temperature should my heat be blowing?

Heat pumps usually produce air that is 85-92°F. This is plenty warm to heat your home to your desired 72°F. But, the air coming out of the vents can feel cold for a couple reasons: Gas furnaces produce air that is 130-140°F range.

Why is my furnace blowing too much hot air?

If your HVAC unit is blowing hot air, the first thing you should do is check the air filter. AC systems need to have a free-flowing supply of air. Dirty filters limit this flow, causing a strain on the system until it reaches the point where it can't keep up.

How hot should air coming out of vents be?

Your personal comfort should always come first, so there isn't a universal fixed temperature recommendation. However, it's best to have a 16 to 22°F difference between your supply air and return air temperature when you set your thermostat.

How is ductwork tested within a furnace?

The test involves pressurising the duct system with a high accuracy volume flow measuring device that simultaneously measures air flow and its effect on the pressure within the duct system. The tighter the duct system, the less air you need from the fan to create a change in duct system pressure.

How hot should a furnace get?

Most recommend keeping your furnace between 68 and 70 degrees. You will find that after about a week at a lower temperature, your body becomes accustomed to it, and it no longer feels cold to you. You will also be surprised what some cozy sweaters, socks, and throws will do to keep you warm and comfortable.

How to tell if a thermostat is bad?

A bad thermostat can be detected when your AC or furnace is not turning on, your HVAC systems are not turning off, the thermostat not responding, your HVAC system is short-cycling, the room temperature not matching the temperature displayed on the thermostat, and the programmed setting resetting themselves.

Why is my air not coming out hot?

Make sure to replace filters every three months to maintain optimal performance. Issues with the pilot light, high limit switch, blocked burners, leaky ductwork, electrical problems, and blower motor failures are common reasons for HVAC systems blowing cold air.

How can I increase the air flow to my furnace?

Improve Airflow with a Booster Fan

Installing a booster fan in your HVAC system ductwork will increase airflow to rooms that are struggling to get warm air. A booster fan is a DIY trick that homeowners can use if they don't want a complete overhaul of their ductwork.

What should the supply temp be for a furnace?

The highest allowable supply air temperature for that unit would be 125, with the ideal being 110. We can attempt to do that through a combination of proper commissioning practices, primarily setting the airflow properly in heating mode.

What should the temperature difference between the supply and return air vents be?

While there isn't any perfect temperature you should set your HVAC system to, there is an ideal temperature difference between the supply and return air, which should be between 16 and 22 degrees Fahrenheit. This difference in temperature is the evaporator Delta T.

What is the most common cause of poor air flow in a duct system?

Obstructed Vent

One of the most common causes for poor airflow is a blocked vent. To properly heat or cool your home, the air needs to be unobstructed. To see if there are any blocked vents, look by the baseboards or on the ceiling. Furniture, bedding, and the vent damper could all be possible obstacles to the vent.

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