I am in Michigan (Southern Part) and use inside air. I have some water
accumulation during the fall and spring, but when the winter comes
around, much less. I get some ice that forms at the base of the
greenhouse between the layers of the plastic.

I have used outside air, and gotten exactly the same issue, and in the
summer had as much as 6 inches of water between the layers of plastic,
which caused me to add a drainage hose to each side of the greenhouse
(It can get very humid here).

I went back to inside air after 2 years of experimenting with outside.

My reasons are simple:
1) Inside air means that I know the humidity of the air between the
plastic
2) I know what might leak back into the greenhouse from a cut in the
plastic
3) I know what insects might get in from the air
4) When I get heavy snow, I can turn up the heat early and get the snow
to slide off the plastic, rather than have to let it sag to the inner
plastic to get warm enough to slide off
5) In an ice storm the air is warm enough between the two layers to keep
most of the ice from sticking, so it slides down and does not cut up my
plastic as it shatters in the wind

Doug

In article ,
"David Jewell" wrote:

Pat thanks for the response, can I ask where you are from (aka do you have
the nasty cold freezie winter) I have had some water accumulate near the
ground in the bubble and thats what inspired my question.

Thanks

"Pat Brennan" wrote in message
...
All the books say draw the air from the outside, every greenhouse I have
seen draws from the inside. The blowers sold for inflation are made to go
on the inside and use inside air. I have never had a problem and all my
greenhouse use inside air. If you are not having problems with water and
things growing between the layers, I would not worry about it.

Pat

"David Jewell" wrote in message
.. .
I put a greenhouse up this summer and am confused about a point and was
wondering if anyone could answer this one for me. I currently inflate
the
greenhouse with air from inside the greenhouse but have been told I
should
be drawing air in from the outside.

With drawing the air from the inside I am thinking that the bubble will
be
warmer and give me better insulation but I am concerned with the issue
of
water collecting in the bubble. With drawing air from the outside I am
thinking that the air will be a lot colder and thus not so good for my
orchids.

Any advice would be greatly appreciated.

Dave (Ontario, Canada)