Hi guys, thanks for your help in advance. I just had a new 1.5 ton Trane air handler and condenser installed on my 2nd floor closet space. It was just a swap out of a very old unit that was on it's last leg. Unfortunately, the company installed the air handler, but did not include an air filter! I asked the installer and he said he didnt have one of the size. 19"x21"x1". I immediately shut the A/C off and went to home depot and did not find that size, but found an 18"x20"x1". Here are my questions: 1) Even though the 18"x20"x1" does not fill out the metal filter holder, it appears it covers the majority of the air going into the blower. Can I run this for a week or so until I receive 19"x21"x1" in the mail from a custom order? 2) Is it unusual for the air filter slot not to have a cover in front? My last A/C did and my one downstairs does (see pic of old A/C last picture) 3) Is it typical when the A/C is on for the air filter to in essence rise upwards from the metal slot it sits up to the blower? 4)What's the cut out and what appears to be a duct up in the ceiling?

I have a warehouse space that is about 2500 sq. ft. with 20 ft. high ceilings and a dock. I am looking at options to cool the space. I don't have a layout floor plan right now but I can provide one if necessary. I checked out HVLS fans like Big Ass Fans but they are very expensive so I wanted to see what else is out there. Maybe something like a few smaller fans strategically placed around the warehouse to push the warm air out. I am not really sure though Any help would be appreciated. Thanks.