Aircraft heater attachment door

Not exactly sure where it’s located tried looking for a picture on line but couldn’t find nothing. I know there is a spot that is missing on the aircraft I believe that you can hook up aircraft heaters towards the front on the Boeing 737’simage

Are you talking about when the plane is at the gate and they hook up a big hose with air in it to the plane for climate control?

Yeah so the plane isn’t ice cold when pax board the aircraft I see it every day I’m at work just can’t think of the spot that it’s at 😒

I know on a b767 it’s halfway between the cockpit and engine.

I wanna say on the 737 it’s a little in front of the main Landon gears?