Why does my furnace look like it sucks air in from air vents?

[Eron A.]

Im looking at my furnace, and I see which way the air is blowing....based on the direction of the filter AND the fact that the filter air arrows are pointing towards the furnace.

BUT...when I follow the ductwork, it looks like the air is getting sucked in from other vents that should have air blowing out of.

It looks like this: AIR VENTS <- FURNACE <- FILTER <- DUCT WORK <- AIR VENTS

That makes no logical sense to me. This is a old house...and I can provide photos.

[Bill B.]

You forgot to put where you are in your profile. That would help people familiar with properties in your area. (Age, builders, style, HVAC systems, etc.)

In vegas we have two giant air returns in our hallways and air registers in every room. (homes are less than 20 years old have combination heat/cool units. )

In MN where I grew up in my parents home there is an air return and an air register in every room. (These are 70 year old homes that might or might not have air central air/heat when they were built.)