how to check if furnace is working

2 min read 04-02-2025

Is your furnace blowing cold air? Don't shiver in the cold! This guide will walk you through how to check if your furnace is working correctly and what to do if it's not. Knowing how to troubleshoot common furnace problems can save you money and keep you warm all winter long.

Signs Your Furnace Needs Attention

Before diving into checks, recognize the warning signs a malfunctioning furnace might exhibit:

Cold air blowing from vents: The most obvious sign. If your vents are only blowing cool or cold air, something's wrong.
Strange noises: Loud banging, rattling, or squealing sounds indicate potential problems that need professional attention.
Furnace cycling on and off frequently: Short cycles suggest inefficiency, potentially due to a dirty filter or other issues.
Higher energy bills: Unexpected spikes in your heating bill could mean your furnace isn't operating efficiently.
Gas leaks (natural gas furnaces only): Smell gas? This is a serious issue. Evacuate immediately and call your gas company.

How to Check Your Furnace: A Step-by-Step Guide

Let's tackle how to perform basic checks on your furnace:

1. Check the Thermostat

Ensure it's set correctly: Double-check that the thermostat is set to "Heat" and the temperature is higher than the current room temperature.
Check the batteries: Replace the batteries if necessary. A dead thermostat won't send the signal to start your furnace.
Test the thermostat: Try slightly adjusting the temperature up or down. If the furnace doesn't react, the thermostat might be faulty.

2. Inspect the Air Filter

Locate the filter: The air filter is usually located within the furnace itself or in a return air grill. Consult your furnace's manual if you're unsure of its location.
Check for dirt: A dirty filter restricts airflow, reducing efficiency and potentially causing cold air. Replace it if it's visibly dirty or clogged. (Ideally, replace filters every 1-3 months depending on usage and type).
Change the filter: Follow the instructions on your filter packaging for proper replacement.

3. Examine the Pilot Light (for older furnaces)

Locate the pilot light: This is usually a small flame near the burner.
Check for a flame: If there’s no flame, refer to your furnace manual for instructions on how to relight it. (Never attempt to relight a gas furnace pilot if you smell gas; call a professional).
Observe the flame: A weak or flickering flame is inefficient. A strong, steady blue flame is ideal.

4. Listen for the Blower Motor

Turn on the furnace: After checking the thermostat and filter, turn on the furnace.
Listen for the blower: You should hear the blower motor running. If it's not running, there might be an electrical issue, or a problem with the motor itself.

5. Feel the Air Vents

Check air temperature: Feel the air coming out of the vents after the furnace has been running for a while.
Identify cold air: If the air is significantly cooler than the temperature set on your thermostat, there's a problem that needs professional attention.

When to Call a Professional

While you can perform these basic checks yourself, some problems require professional help. Call an HVAC technician if:

You smell gas.
The furnace is making unusual noises.
The furnace is not producing any heat.
The furnace is cycling on and off frequently.
You've checked everything and still have cold air.

Regular maintenance, including annual inspections by a qualified technician, is crucial for keeping your furnace running efficiently and safely throughout its lifespan. This preventative maintenance can help detect small problems before they turn into major, expensive repairs. Remember, safety is paramount when dealing with gas appliances. If in doubt, call a professional!