If there are no arrows on an air filter for your furnace how do you know which way to put it in.

Can you post a pic of your filter. Most likely, if they don't have an arrow, then it doesn't matter which way you install it. Looking forward to the pic. Lee.

If your filter has a mesh on it or on one side, that side goes toward the furnace,as that is the stronger side of the filter,, hope this helps

We cannot find the furnace filter on our Lennox electric HP25-311-2P unit. Where is it?!

Somewhere, in the return air ducts, or inside close to the blower,or inside the gigger return vent,, or maybe someone took t out and threw it away, in this case you need to get one