Where is the filter located for an Armstrong Ultra V Tech 80 furnace? How often should it be changed? This is a forced hot air system. Also has central air. Can they be purchased locally ie: Home Depot or Lowe's? Tha nk you.

filter location=somewhere in the return air part of the system,, probably around the blower motor section or possibly behind return air grill
change as often as needed,, look at it once a month and decide,, its pretty important in taking care of your system
yes most Home Depot and Lowe's sells them

Thank you for reply. It is greatly appreciated.

Glad to have been of help