I believe that this "Heaven" is not the same "Heaven" that God dwells in. This is a firmament (or a layer) of water which is above the earth (which was also a layer of water in verse 7). This layer of water or firmament above was called "Heaven".
I also believe that this layer of water or firmament disappeared during Noah's flood. The "Heaven" was emptied during this time.
11 In the six hundredth year of Noah's life, in the second month, the seventeenth day of the month, the same day were all the fountains of the great deep broken up, and the windows of heaven were opened.
12 And the rain was upon the earth forty days and forty nights.
What remains of "Heaven" after the flood could well be our atmosphere. This interesting definition of "atmosphere" is also found in JFB commentary, although not interpreted in the same manner, for [Genesis 1:6].
(firmament--an expanse--a beating out as a plate of metal: a name given to the atmosphere from its appearing to an observer to be the vault of heaven, supporting the weight of the watery clouds. By the creation of an atmosphere, the lighter parts of the waters which overspread the earth's surface were drawn up and suspended in the visible heavens, while the larger and heavier mass remained below. The air was thus "in the midst of the waters," that is, separated them; and this being the apparent use of it, is the only one mentioned, although the atmosphere serves other uses, as a medium of life and light)
Whichever it means, I believe that this firmament is not the same "Heaven" as we refer to where the throne-room of God is.