"I have an old airplane altimeter that I used to conduct the experiment that you described.
I placed it in the freezer first and then noted the pressure reading, then I placed in an oven that was first heated to 200 degrees.
The pressure difference between the cold and the hot areas was approximately one fifth of a foot in altitude."

I doubt this would occur unless you left your airplane altimeter in the oven or freezer for enough time that the temperature was distorting your measuring device- it might not have this affect if you put it in there for about a minute or less.

"The test is not very scientific because the moisture of the air in each location was not controlled and the reading was close to the resolution of the altimeter, but it does prove that the air becomes less dense and therefore exerts less pressure when it is heated in a open environment."

I'm not sure if it proves anything, but there is no question in my mind that density of the air is less in oven and there is more density of the air in a freezer.