Furnace humidifier filters should be changed at least every three months so they work efficiently. If not changed they trap dust and particles that can 'pollute' the air you breathe. http://yourfilters.com/
Filters-Now.com is a great website to find all furnace needs. There is a special section for humidifier filters. And they have delivery available within 24 hours.
Provided your furnace has a humidifier on it, you may replace the filter. I would recommend going to a local home improvement store to find the model that will fit your furnace. If you do not currently have a humidifier on your furnace I would recommend contacting a local furnace supply company to enquire about a new furnace or upgrade.
You can find replacement filters for a Hunter humidifier from many places. The first port of call would be the place you bought your humidifier from, as they normally stock spare filters. Alternatives include big electrical stores and online resellers.
Browse sites like Amazon. These kinds of sites make it easy to compare prices between retailers and vendors. Diyornot.com can also help you decide whether or not to save money and install the humidifier yourself.
Home humidifier filters can be purchased online from Amazon, homedepot, lowes, walmart and sears. Or if you are in the U.K; Homebase, Argos and Boots. You can also search the brand name and model number to find out which local stores stock filters, that suit your humidifier.
There are several places one can find replacements for 3M furnace filters. One can try local home department stores such as Home Depot or order online from Amazon or eBay.
Inexpensive furnace filters can be found at most mass retailers, such as Wal-Mart, Target, Home Depot, and such. If you perfer not to drive, you can find them rather inexpensive online at Amazon and Ebay.
Many different warehouse stores such as Sam's Club and Costco sell these filters in bulk. You can find out more by going to their websites.
Home Depot sells hepa furnace filters online. Have the correct size of filter needed and look for promotional codes for free shipping. If Home Depot does not have what you're looking for, try Sears.com.
You can find a new furnace filter at any major home improvement store. looking online is your best option for starters because they sell the cheapest but not the best quality.
You can find more information about vacuum furnace system at their website. You can read customer reviews on reviews websites and decide if that product is right for you .
One can find more information about carrier furnace parts at several online sites. Some of these sites are "Repairclinic", "Theacdoctors", and "Searspartsdirect".