Furnace and humidifier preparation for winter begins with the cleaning instructions in your furnace manual. Or try these tips if you cannot find it. These suggestions in no way replace having a licensed heating contractor fully check out your furnace.
Clean the blower compartment by lifting off the lower door (blower door) and vacuum the bottom area. Change the furnace filter and set up a schedule to check and change it every one to two months. Lubricate the fan motor if it does not have permanently sealed bearings, and replace any frayed fan belts.
Turn on the water to the humidifier and check for leaks. There are two common types of humidifiers; a drum style that rotates a foam media in a reservoir of water and a flow-through where water from a solenoid valve flows through a mesh media.
In either case when the media fills with rust and scale, they will have to be cleaned or replaced to continue to get humidity into the air. Vinegar, rust and lime remover and humidifier cleaner all help to clean media, floats and pans. Take your time to get most of the scale and mineral deposits out of the pan and other parts to minimize bacteria and mildew habitats. Use of a bacterial-control during the heating season will insure a safe source of humidity.
On drum type humidifiers, check the water level so it is below the overflow tube in the reservoir. Media, floats, valves, washers are all usually replaceable and can save the handyman lots of money.