I have heard that it's not a good thing to put soot sticks (by Chem Vac soot and
Creosote remover sticks) in your furnace for cleaning. My furnace guy told me that.
But, I am wondering if that's true or not. I have heard some good things about soot
Sticks. So, my question is do soot sticks help or hurt your furnace.

Thank you so much.

I see the word Furnace but many people call a boiler a furnace. So what exactly do you have?

Personally I don't believe in soot stick but have used them. You didn't say what unit you have. I'm assuming oil-fired heat. ( gas burns very clean)

The Best way to completely clean out soot from older boiler/chimney is remove metal top boiler covering. Under that you will see plate(s) that's above the jackets, gently remove those to expose the actual boiler jacket segments. To clean between them use a rod that looks like a long pipe cleaner and rod down between the jackets of the boiler. Those rods are sized for different boiler jackets to match jackets widths. After this is done you need to clean out the soot that dropped to the bottom of the heat chamber soot is flammable. That done we use either refectory cement or we use Smooth coat over the metal plates you reinstalled.

While we are doing this we also pull the metal galv smoke pipe(chimney from boiler to actual hose chimney) After pulled you can clean out the actual House chimney that soot sticks wont get rid of. Also now you can use a mirror to inspect lower chimney and see if threes any masonry pieces that dropped down the chimney that may warrant a full chimney inspection

http://www.buyinsulationproductstore.com/servlet/the-410/Smooth-Kote-Calcoat-127/Detail

The problem with soot sticks is that it can't clean out the heavy soot in bottom of chimney and doesn't address other issue that could be there. True story I was ion a jobsite installing a new bathroom and the owner had a service contract for his boiler, Tech installed new burner nozzle tip, cleaned electrodes, new oil filter, adjusted burner air flow, then threw in smoke stick and all hell broke loose. The chimney was very restricted and the soot stick chemicals back flowed into the house when it loosened up all the soot. Tech left and said need chimney sweep. Well that me lucky for my customers. I couldn't unblock the bird's nest with my chimney brushes and even just using the rods. I had to use a bow and carp arrow to shoot past that heavily blocked area. Unblocked it but now the Tech had to come back out because he set the air flow on a restricted chimney which now opened changed the flame tip in more oxygen being more air flowing up the Chimney.

I realize this as a home owner your probably will never do this but you now know what how too professionally clean out soot from a boiler. Now if you have oil forced air the heat exchanger is completely different and doest soot as bad but that exhaust smoke stack and house chimney needs to be periodically cleaned.

I see the word Furnace but many people call a boiler a furnace

Hope this helps you out

Most furnace & boiler manufacturers say not to use them.

I agree but in the 80s this was common