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.
That will depend entirely upon the type of furnace you have. There are filter less furnaces, so if you have one, you won't need filters. Otherwise, if your furnace requires a filter, you will need to purchase filters and replace them regularly. If you have the owners manual, that will tell you if the furnace needs a filter.
There are many places to find gas furnace prices. One can look on sites like Furnace Price Guides, Century Gas Furnace, and Consumer Reports. One can also find gas furnace prices by going to a local heating supply store.
One can find good water filters from many local shops, but there are many online websites where one can find lots of good water filters. Amazon would be one of them.
Remove the top panel and look up inside. There will be two filters in a V pattern.....unless you bought a forclosed house, then there might not be any filters. In that case, look for channels in the middle--one angled to the left on the left side and one angled to the right on the right side. The top of the filters will just lay over and touch the sides of the furnace.
One can find reviews for charcoal filters on websites which sell charcoal filters. They are also published in certain specialist magazines and publications.
One can find Fridgidaire filters on websites such as amazon, eBay, partselect, etc. They provide different types of filters from big to small to fit with different fridges.
You can replacements for Haviland china at one of two really good places. The first one would be directly from Haviland and the other one is a website called Replacements. They have replacement china from all manufacturers.
At the bottem right hand side facing the furnace you will find a filter. This is one of the commen filters you can buy at Walmarts. The filter is a cardbord sheet with a filter on it. Pull out said filter look at the size printed on it.Go to Walmart and buy another. When you push in said filter be sure the air flow arrow on top edge is pointing toward the furnace.
On the inside of one of the removable panels
The best place to find information on repair parts for your furnace, is to check the site, of the compnay which you own the furnace from. This will lead you to the right place to purchase replacement parts.
Electric furnace prices can be found anywhere an electric furnace can be purchased. One place to look is at a home appliance store, such as Lowes or Sears.
One can find more information about carrier furnace parts at several online sites. Some of these sites are "Repairclinic", "Theacdoctors", and "Searspartsdirect".