Why Hovind's Canopy Hypothesis Doesn't Hold Water
Once upon a time, there was a hypothesis formed. This hypothesis tried to explain a very literal reading of Genesis 1:6-7. The itsy bitsy spider would have drowned with the amount of rain in this canopy.
I'm a scientific layman, so let me to defer to Dr. Hugh Ross who brilliantly explains
Some young-earth creationists [Neo-Ussherians] attempt to explain long life spans [Genesis 5] prior to Noah's flood and huge hydrocarbon and limestone deposits by proposing that a thick water canopy once surrounded the Earth.
They claim such a canopy would shielded life from radiation, greatly extended human longevity, created a warm, humid environment to augment Earth’s biomass and, once collapsed, suddenly inundated Earth's entire surface,destroying all life (except that on the ark) and even much of Earth’s topography.
This hypothesis fails every plausibility test. First, a canopy with enough water to cover Earth would either dissipate to interplanetary space (if it were vaporous) or come crashing down under gravity's influence.
A vapor canopy, even if it existed for a short time, would have set up such a powerful greenhouse (heating) effect that no ice or liquid water would remain on Earth to sustain life, making the flood unnecessary.
If the canopy were liquid or ice, converting the ice to liquid or liquid to vapor would consume so much heat as to freeze all life on Earth.
Again, the Flood would be unnecessary.
Increasing Earth's surface heat and humidity by just a little would increase the total living biomass by only a small amount. Earth's surface area and solar energy flow limit the living biomass to a quantity far below what is needed t explain all earth's biodeposits within a time span briefer than million years. Although a vapor canopy would provide some protection against ultraviolet radiation, it would not impede the hard cosmic ways hat fundamentally limit human life spans to about 120 years. (Words in brackets mine)
Kent Hovind has said on multiple occasions that he was a science teacher, so he should know better.
Basil (4th century) anticipated this idea and stated
“Here then, according to me, is a firm substance, capable of retaining the fluid and unstable element water; and as, according to the common acceptation, it appears that the firmament owes its origin to water, we must not believe that it resembles frozen water or any other matter produced by the filtration of water; as, for example, rock crystal, which is said to owe its metamorphosis to excessive congelation, or the transparent stone which forms in mines. This pellucid stone, if one finds it in its natural perfection, without cracks inside, or the least spot of corruption, almost rivals the air in clearness. We cannot compare the firmament to one of these substances. To hold such an opinion about celestial bodies would be childish and foolish.”
Hovind's problem here isn't just eisegesis, but his insistence that the KJV is the only inspired version.
Even though KJV-Onlyism is outside the scope of this article, I will for the sake of argument, show that even If I only use the KJV, the canopy is an improbable exegetical formulation.
We see from this passage that this “firmament” -whatever that is, divides the waters. Some water is UNDER it and other water is ABOVE it. 
There are many problems with this interpretation.
For example: The waters would be in the same area as the birds, so you either had birds flying through the water (Genesis 1:20) or you have it at such a level that it blocks the view of the stars, which would contradict Genesis 1:14-18.
Hovind has said that it was above the stars. However, not only is this very scientifically improbable, it is a unfalsifiable hypothesis at this point and is speculation that can't be demonstrated from scripture.
It never says the water was above space, it says the firmament in the KJV, which contextually is referring to the sky (i.e. our atmosphere).
But Hovind conveniently limits only the KJV's wording here, because it becomes a debate over semantics instead of what the text actually means. (Like quibbling over heaven vs heavens in Genesis 1, even though the KJV reads heavens in Proverbs 8:27-28)
It is interesting that Hovind cites Psalm 148 because it actually questions his position since David is speaking post-flood.
Why are these waters still there?
Just how much water is up there?
Again, these are speculations about the text, not what the text teaches.
Job 38 mentions water jars, do you believe there are actually water jars in heaven? If so, inform the hipsters drinking out of jars, because heaven did it first.
We therefore insult the text when we try to apply literal meanings to poetic language. It's the equivalent of saying when the Bible says "your eyes are like doves" the man thinks her eyes are literal doves. (Song of Solomon 1:5)
Though I haven't seen Hovind use this particular objection, I mention it because it seems to be a popular layman "evidence" for the canopy theory.
When the Scripture says "floodgates" or "windows of heaven" like in Genesis 7:11, It is a metaphor.
There are not literal floodgates or windows holding water, in the same way, Jesus is not literally a door.
The scriptures also say blessings come through these floodgates, (2 Kings 7:2, Malachi 3:10), are the physical manifestation of blessings being held behind this gate? It is more probable that this is a figure of speech.
There are many different models of what this could be, perhaps the answer is as simple as clouds.
Clouds are a collection of water particles and when looking up in the sky as it's raining hard, a modern day author explaining this could say "It is like someone opened the floodgates in the sky" would be an acceptable metaphor to convey the meaning.
The Canopy hypothesis has many holes and it lacks historical backing. It is both scientifically and exegetically improbable and it creates more problems than it solves. We do not need such speculation in defense of the faith.
 A Matter of Days by Dr. Hugh Ross p. 98
The Hexaemeron: A Select Library of Nicene and Post-Nicene Fathers of the Christian Church, Edited by Phillip Schaff p.67
 2peter3.com "Dr. Kent Hovind Proves Canopy Theory Using the KJV Bible"