LOL....sorry....I really did think you were joking. So, if you've already got the old filter out, can you turn on the furnace and feel which way the air is flowing? If hard to tell, hold a piece of thread or a strip of TP. My filter goes on the supply side - so the filter arrow points into the fan. If it is still unclear, you can probably follow just a bit of ducting to see which way air is moving through the furnace. There also may well be arrows either where you slide a filter in; or along ducting into or out of the furnace.
dstieger wrote: