Q&A for How to Clean a Furnace

Yes, dirt caught in the vent of the furnace could back up the system and eventually stop it from turning on.

Yes, try a shop vac from your local hardware store. Those work well.

Sounds like there is not enough return air. The unit can only blow out as much as it can pull in, if there is not enough return air or the return vent is not large enough, the unit will pull harder on the filter. It will also be less efficient.

The fan will turn on prior to the furnace firing for safety reasons. There is typically a short delay between the stages.

This depends upon the situation. If it happens after the heat has been on for a while, it is likely expansion and contraction of the ducts, which is harmless. However, if it is immediate, and sounds like a violent "whoosh" (in natgas, oil, and propane furnaces), you should call an HVAC technician.

The furnace should optimally be cooled to around 20 degrees Fahrenheit or less.

First turn off the power to the furnace for safety. Locate the sensor, which is usually a thin metallic rod near the burner assembly. Remove it carefully, then gently clean it with fine emery cloth or light sandpaper, followed by wiping with a dry cloth.

That suggests several issues: dust burn-off, mold or mildew in ductwork, electrical issues, or a gas leak. Dust burning off usually goes away quickly, but a musty smell may require cleaning ducts and replacing filters. A strong acrid smell suggests an electrical problem that needs immediate professional attention. A sulfur-like smell could indicate a gas leak, which is very serious.

See that your air filter is clean and properly installed, as a dirty or clogged filter can restrict airflow. Inspect the ductwork above the coils for blockages or leaks, such as disconnected joints or obstructions. Make sure the fan motor is working correctly and the fan blades are clean. Verify that your thermostat settings are correct for cooling.

If one of your vintage gas burner flames is not full even after cleaning, there might still be an issue with the gas flow or the burner itself. Check if the burner cap is properly aligned, clean the burner ports with a needle, and make sure there's no obstruction in the gas line specific to that burner.

The average cost of furnace cleaning can vary depending on your location, the type of furnace, and the extent of cleaning needed. Generally, you might expect to pay between $100 and $300. Basic cleaning typically falls on the lower end, while more comprehensive services like inspections and repairs can push the cost towards the higher end.

Using canned air can be a convenient way to clean dust from your furnace, especially in hard-to-reach areas. Make sure to turn off the furnace and disconnect power, open the access panels, and use short bursts to avoid moisture buildup. Focus on sensitive components and ensure good ventilation to avoid inhaling dust.

Dirty blower blades in your furnace can indeed reduce airflow, causing several issues. When the blades are coated with dust and debris, they can't move air as efficiently. This inefficiency forces the blower motor to work harder to circulate air, leading to increased strain. Over time, this extra strain can cause the motor to overheat and potentially trip the circuit breaker as a safety precaution.

The flame sensor most likely has build-up on it, meaning that it needs to be cleaned off with fine steel wool.

Fully removing your furnace heat exchanger is not advisable unless you are a professional. On a side note, it is also not a standard part maintenance suggested by any manufacturer.

Concern yourself first and foremost with removing the burners from the manifold, turning upside and knocking the grit clear of the ports. That big yellow flame you see is offgassing carbon monoxide. Reinstall and look for a steady blue flame, adjust your manifold vents for the proper mix of primary air. Secondly, make sure you check your blower and motor for dust build-up. Also check your fan belt for glazing and cracks.

The filter will be installed before the blower, and the arrow will point toward the blower.