The main question would be whether or not your fan is capable of inflating it. Since there are lots of different fans out there and lots of different shapes and ways greenhouses are built/sealed your best bet would be to simply try a splitter and inflate both at the same time to see what happens.

Fans are rated by CFM (The volume of air (measured in cubic feet) that can pass through an opening in one minute.) under a certain amount of pressure. If there is too much pressure, like from it trying to inflate too much plastic, then the less CFM and will not be able to inflate the entire layer of plastic.

Also be aware that a lot of these fans/blowers greenhouse places sell are just computer fans or blowers with some extra plastic pieces on it to direct the airflow and maybe a mount for the fan. You can save a lot of money by going this route.. You could simply find a more powerful blower/computer fan and stick it in the housing you have if you find it won't inflate both layers.

I'm looking into using a DC fan to inflate my greenhouse so that it can be run off of battery and PV panel. Still investigating this.

If you have several inches of air space separation on one side of your 3-layer cover, there would be little added benefit by also inflating the other side. The commercial squirrel cage fan of 60-100 CFM is used for structures up to 3000 square feet in size, so you can use a much smaller one. The internal pressure should be 0.25 inches of water
( measured with a manometer). If you apply more than that , the plastic will fail sooner.

Thanks for the recommendations. I have quite a few small squirrel cage type fans to use so I probably won't be using a computer fan. Previously I had used an old bathroom ceiling fan just setting on a crate blowing air toward the boxed opening in the inner film layer. It failed in my bathroom after only 10 years but after oiling it ran continuously in this greenhouse for another 12 years. Now I want to move on to a more suitable system.

Rather than splitting the hose, you could simply make penetrations through the bubble wrap so the pressure would equalize on both sides. You probably would gain very little or nothing from inflating the second side, in any case.

I'm not following why having two air layers wouldn't be better than one. Perhaps in a warm climate it would make no difference but I would think in the northern states it would over the winter at least. Isn't that the reason some of us have triple pane windows up north? :)

Your triple pane windows are indeed good insulators. The amount of air space between the panes is probably 1/4 to 5/8 inch. That is the most efficient space. In fact, air space r-values from 1/2 inch to 4 inches are all almost the same, 1.00-1.05. Thus more is not better, or at least efficient, with air space for insulation.

Here is a link that might be useful: r-values of air spaces

That r-value table is very useful. But now it still seems important to blow some air on both sides of the bubblewrap. Since there is a membrane covering the bubbles I hope to accomplish multiple air pockets. From Outer surface my pattern might be:

1. outer 6 mil film
2. 1/2-2" air space(inflated)
3. outer film of bubble wrap
4. air pockets of bubble wrap(fixed)
5. inner film of bubble wrap
6. 1/2-2" air space(inflated)
7. inner 6 mil film

Are you stating that I am better off without #2 or is your reasoning that there will possibly be enough gap between #1 and #3 that #2 will be present without inflation? I Already cut plywood plates with 4" duct holes to clamp the layers together (#3-7 and #7) so possibly just lining up those plates may be sufficient to accomplish adequate airspace. Maybe they won't even need to be alligned? What your opinion on this method?

Depending on what plants you are planning to grow, all those layers of plastic and bubble wrap will significantly reduce the amount of incoming light. As I mentioned, any air space larger than 1/2 inch does not add to the insulation properties.

I wanted to thank all for their comments and offer a few experiences with this setup. I've been inflating the structure now for a few weeks with a small double squirrelcage fan that alligns to both inlets almost perfectly.

What I notice with the inflation on both sides of the bubblewrap is that there is considerable balooning between arches and hardly any noticable gap over the arches. So the air spaces range from almost nothing to ~4". I have no idea of the R value but when I compare the heat retention of this structure to my others, a double poly and a single poly, this one really holds the heat superbly over nights.

Installing the three film layers was difficult with the wire-lock channels. I really had to apply pressure as I inserted the wiggle wires (one set) especially over the seam of the MagniClear Pool Cover(bubblewrap). Earlier this spring I installed a double 6 mil poly layer over another structure but I first wire locked films over the peak to point of rollup sides. Then wirelocked the double rollup aprons on top of that. My point is that 4 sheets if 6 mil film held in with two wires in the same channel is much easier to install than the two 6 mil films and bubbblewrap with a single wire. Regardless, both methods are doable for those interested.

As far as light transmission I haven't noticed any real difference. We've been bringing plants into this benchtop greenhouse almost daily and hardening plants with the intense sunlight has been typical of experiences with just double poly film covering. Most often we have been setting flats under benches in shaded areas until they adjust.