Q&A for How to Clean a Furnace

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Could dirt prevent a furnace from turning on?

Community Answer

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

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Question

Can I vacuum the vent of a furnace?

Community Answer

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

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Question

Why is my furnace pulling the filters apart and blowing dust into my home?

Community Answer

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.

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Question

Why does my furnace blow out cold air before it blows out hot air?

Community Answer

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

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Question

What does it mean when I turn on the heating system and it makes a boom sound?

Community Answer

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.

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Question

Should the furnace be warm when cleaning it?

Community Answer

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

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Question

Which way does the arrow point when replacing the airflow filter on a furnace?

Community Answer

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

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Question

How do I deep clean a furnace? What do I need to clean in a furnace?

Community Answer

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.

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Question

What tools do I need to remove the heat exchangers as suggested? I have a 97% efficient furnace. Will it void my warranty if I disassemble my furnace?

Community Answer

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.

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Question

What does it mean if my furnace works fine for a few sessions but stops working after that?

Community Answer

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

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