Why is my furnace running but the house is cold?

Author: Jean Roob Jr.  |  Last update: Friday, March 28, 2025

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 running but not getting to temperature?

If your furnace turns on but no heat is produced, there may be a problem with the fuel supply or the ignition system. If something is stopping your furnace from receiving gas, there is no fuel to combust so the furnace will not create any heat. The furnace turns on but no heat comes out.

Why is my furnace not keeping the house warm?

Check the air filter first

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. Change the filter for a clean one if it's clogged, and continue to change it every 1 to 3 months while the furnace is running.

Why is my house cold even with heat on?

Your house may not be heating up due to several reasons: a malfunctioning thermostat, issues with your heating system, blocked air filters, or inadequate insulation. It's important to check these components to identify and resolve the problem. Let's dive into each of these potential issues to see which one is yours.

Why is my furnace on but not heating my house?

The first step in diagnosing the issue is to check your thermostat settings. Ensure that it's set to “Heat” mode and the desired temperature is higher than the current room temperature. Sometimes, the thermostat might be accidentally set to “Cool” or “Fan Only,” causing the furnace to run without heating.

Furnace blowing COLD air out vents - 3 MOST common causes!

Why is my furnace working but my house is cold?

Get your ductwork checked. 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.

Why is my furnace not pushing out heat?

Check Thermostat Settings: Ensure the thermostat is set to “heat,” and the fan is on “auto.” Inspect Air Filter: Replace a dirty or clogged air filter with a new one. Relight the Pilot: If you have a pilot light, follow the manufacturer's instructions to relight it.

Why is my house not warming up with 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 does my house still feel cold at 73?

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.

Why is my house colder than my thermostat setting?

Dirty or worn flame sensors, blower motor problems, clogs in the condensate lines, and electrical issues are some of the many problems that can leave your HVAC system failing to deliver the temperatures you've programmed in your thermostat.

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 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 heat coming out cold in my house?

If your furnace is blowing cold air in your home, this is a sign of an issue with the flame detector, gas supply, air filter, pilot light, or condensate lines. Many of these issues are able to be easily solved on your own by sanitizing or replacing components in the gas furnace.

Why wont my furnace keep my 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.

How do you know if you have a bad flame sensor?

Short cycling is a common sign of a bad flame sensor. The sensor thinks that there isn't a flame, so it shuts off the gas as a safety mechanism. Except, there is a flame and without the gas to supply it, it dies. This is a frustrating problem, but an HVAC technician can fix it.

How do I know if my heater needs professional service?

If you don't want to be in a fix during winter, here are some signs that your heating system needs repairs ASAP.
  1. Outrageously High Power Bills. ...
  2. Your Burner Flame Turns Yellow. ...
  3. Strange Noises from Your Furnace. ...
  4. You have to Adjust Your Thermostat Constantly. ...
  5. The Age of Your Heating System. ...
  6. Too Many Replacements in a Short Time.

Why is my furnace working but the house is cold?

If your furnace is working and blowing warm air, but you just aren't feeling it, you may have closed or obstructed HVAC vents/registers. Check your home for any blocked or obstructed vents and registers. You may also have excessively leaky or damaged ductwork.

Why will my house not cool below 74?

Your AC might not cool properly due to thermostat issues, an undersized unit, or extremely high outdoor temps—so check those first. Keep an eye on airflow—replace clogged filters every 3 months, and make sure vents and ducts aren't blocked for efficient cooling.

Why is my house still cold with heating on?

Draughty doors and windows

Gaps in doors and windows let warm air escape and cold air enter. It might be time to weatherstrip your doors and windows or consider replacing them if they're old and inefficient. This not only helps in keeping your home warm but also aids in reducing your energy bills.

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.

How long should it take to heat a house at 2 degrees?

So how fast should a furnace heat a house? On average, once you turn on your furnace, it should take about an hour to increase indoor temperature by 1 degree. Afterwards, it's 45 minutes per degree.

Why is my furnace not heating my house enough?

Dirty air filters are perhaps the most common reason that furnaces fail to provide enough heat to a home. (They're behind plenty of other problems as well.) Over time, this air filter will become clogged with dust, dirt, and other debris.

Why is my furnace running but not producing heat?

Check Furnace Thermostat Settings

Incorrect thermostat settings can be the cause behind no heat coming out of the vents, even with the furnace blower turned on. Check the thermostat to ensure the setting is in HEAT instead of COOL. It is a common mistake that happens. The fan runs continuously when it is switched on.

Why is my house not heating up to temperature?

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.

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