heater a/c vents: floor & ceiling??

[Bobbi]

I had a/c coming from the celing vents in my home, and the heat too when winter began. The floor vents seemed to just be sitting there useless and I figured that these were the old vents (it's a 1974 home) from before central heat & air was installed.
I covered the floor vent openings with a layer of aluminum foil and put the vent back on (over the top of the foil), because I thought maybe a spider or mouse or something could enter the home through this apparently useless vent.
Last night I heard a faint rattling noise, and some warm air was rattling the foil on the floor! Heat is enthusiastically coming from the ceiling vents, but there's also some warm air coming from the floor vents. What's happening on the floor vents? Can the heat come from both areas?
I guess I should take the aluminum foil off?

PS, This is my first winter with this home. Never a dull moment, many questions and mystifying occurrences!!

[Tom]

Bobbi, I have seen this same question pop up from time to time and I dont think I have ever seen a good explanation. Since alot of different manufacturers came and went in that era of homes, it entirely possible thats the way the home came from the factory or as you stated it could have been done later on in the homes life. However if you want to get to the bottom of it, you will have to get under the home and physically see how the vents run. Tom