Why is my furnace struggling to heat the house?

Author: Prof. Ramiro Kautzer  |  Last update: Sunday, July 13, 2025

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.

Why is my furnace not getting the house warm enough?

A dirty filter blocks airflow, which can stop your furnace from heating up all the way. Be certain that you are changing your air filter when needed, as well as check that there are no large objects stacked around the furnace that are impeding airflow. Keep clean ducts and a clear path.

Why is my furnace not making enough heat?

Check the Furnace Filter.

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.

Why is my furnace taking so long to heat my house?

Check the air filter first

The first thing you should do is see if the furnace has a clean air filter. If the filter is heavily clogged with dust and debris, it cuts down on airflow, which in turn means less heated air is getting around the house.

Why is my house not heating up to temperature?

This problem often points to inadequate circulation of warm air. It could be due to blocked vents, a failing HVAC fan, or issues with the furnace itself. Ensure that furniture or drapes are not blocking your vents. Also, check if your furnace's filter is clean, as a dirty filter can restrict airflow.

Top 5 Furnace Problems and How to Fix Them

Why is my house so cold even with heating on?

If your furnace is blowing hot but your home is still cold, it may be a problem with your ductwork. You may have leaky or damaged ducts that are letting hot air escape and cold air in. Sometimes a damper in the system can get miss-adjusted or come loose, thereby inadvertently blocking or reducing airflow.

Why is my furnace not reaching desired temperature?

Clean your Air Filters, Vents, and Ducts – A clogged air filter will struggle to meet the thermostat's set temperature since the dirt and debris buildup prevents air from circulating through the vents. And as airflow into living spaces drops, so do comfort levels.

Why is my heating not reaching temperature?

Radiators might not be getting hot due to trapped air requiring bleeding, a malfunctioning boiler or central heating pump, thermostatic radiator valves that might be stuck or set too low, or the central heating system having sludge or rust which causes blockages.

Why is my furnace not as hot as it should be?

If the furnace is running but blowing cold air, there can be a number of things that have gone wrong, from a change in thermostat settings and a filter that needs changing to a pilot light being out and sensors being dirty.

How long should it take to heat a house at 3 degrees?

Under normal circumstances, once your furnace comes on it should take approximately one hour to increase the temperature by one degree. After that, it typically takes 45 minutes for each additional degree.

Why is my heat barely coming out?

One of the most common issues with a heating system not functioning is dirty air filters. If your air filters are extremely dirty, then the airflow can be blocked. Check for clean air filters, vents, and registers. Make sure there are no rugs or furniture blocking vents or registers as well.

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.

Is it normal for furnace to not keep up in extreme cold?

When temperatures drop below zero or even below freezing for extended periods of time, sometimes your furnace can't keep up. If your home is not heating up to the temperature you've set, try lowering it a few degrees. The temperature of the air coming out of your vents doesn't get warmer by turning up your thermostat.

Why is my furnace on but my house is cold?

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.

Why is my house taking so long to heat up?

sounds like there is a problem with radiators heating the property, this could be one or more of several factors ie, boiler or system control fault, circulation fault or even gas supply fault. An investigation by a professional should quickly be able to diagnose.

Why is my furnace not kicking on enough?

The cause of your furnace not blowing hot air could be the thermostat configuration, a dirty air filter, the high limit switch, a clogged condensate line, insufficient fuel, leaky ducts, ignition problems, a blocked burner, flame sensor issues, gas valve malfunctions, a cracked heat exchanger, or a clogged coil.

Why is my furnace not heating my house enough?

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.

Why is cold air blowing when the heat is on?

You Have Cold Air Blowing Out The Vents When The Heat Is On Because of a Dirty Air Filter. Hiding in the filter of your heating system is dirt and debris. If you aren't cleaning it regularly, this will accumulate over time, leading to problems with your heating system's efficiency.

Why is my furnace not keeping the house warm?

One of the most common culprits when a heater isn't working efficiently is dirty air filters. These can restrict the flow of heated air into your home. Remember, regular checks and replacements are essential for smooth HVAC system operation.

Why is my house not getting warm with the heating on?

If your home isn't warming up as expected, a dirty air filter, blocked vents, or thermostat issues might be to blame. Check and address these issues before considering professional assistance.

Why is my house colder than the thermostat setting?

Your house and attic insulation can wear down over time. Your house also may have hidden attics that aren't properly insulated or uninsulated garage walls that are attached to your home, and this can cause problems with heat escape, unwanted airflow, and drafts. Your ductwork has problems.

Why is my furnace not getting as hot?

Check your thermostat's batteries and replace any that are exhausted or defective. Clean all of the parts of your furnace, especially the ones that are susceptible to dust and dirt. You could also hire HVAC technicians to clean the system thoroughly. Ensure that the gas valve is open and not obstructed by any debris.

Why is my furnace not heating to the set temperature?

Some of the most common thermostat issues include:

The thermostat is not in an ideal location in your home. Your HVAC system isn't large enough to serve your home effectively. Your furnace or A/C is having problems. There are airflow issues due to dirty vents or ducts.

How to tell if a furnace flame sensor is bad?

Top 7 Signs of a Bad Furnace Flame Sensor
  1. Flue Line Corrosion. The flue line is responsible for venting harmful gases from the furnace outdoors so nothing seeps into the house. ...
  2. High Energy Bills. ...
  3. Yellow Flames. ...
  4. Furnace Short Cycling. ...
  5. Dirt on the Sensor. ...
  6. Visible Damage on the Flame Sensor. ...
  7. Age.

Why does my house feel hotter than the thermostat set?

Check for dust, dirt, and other kinds of residue inside the thermostat. Excessive dust and dirt buildup can prevent your thermostat from working properly. Clean any residue you see on the thermostat, and see if that helps improve the temperature in your home.

Previous article
What plants like tomato cages?
Next article
Why is my garage door signal so weak?