There are pluses and minuses to each.

The roof vents work without electricity, so are great to save money, and if
there's a power loss, as you stated. If you are using shade cloth inside
the GH, they also vent away the heat from where it collects - above the
cloth.

I have always preferred the powered ventilation for a couple of reasons - 1)
it gives me more positive control of the ventilation, as I can adjust
thermostats the way I want them (In my GH, one thermostat opens the inlet
and outlet shutters when the inside temp gets to about 70ºF, allowing some
outside air exchange, but the big exhaust fan - controlled by a different
thermostat, doesn't come on until about 85°.), and 2) The shutters can be
covered with screen to exclude insects, a task not easily done with most
roof vents.

--

Ray Barkalow - First Rays Orchids - www.firstrays.com
Plants, Supplies, Books, Artwork, and Lots of Free Info!

.. . . . . . . . . . .
"Lori Siegmund" wrote in message
om...
Another question related to venting.... the gh model I am getting (15'
x 16') has four roof vents and four side vents. Each vent is 1.5' x 4'
in size and weighs less than 8 lbs. with the polycarbonate, I believe.
I am mounting this gh on a 2' concrete base wall. The max height
inside the
gh will be 10.5' since it will be on the base wall. The side walls
will now be 8' instead of 6'.

Do you think the roof and side vents with the solar-powered openers
along with good circulation fans throughout will be enough? Or,should
I also install intake shutters and an exhaust fan as my primary
venting and use the roof and side vents as secondary or backup for if
and when I might lose electricity?

Keep in mind I live about two miles from the coast. It rarely gets
above 85 degrees here and that is on a rare day. Coastal fog in the
AM and PM most days. Any thoughts?

Lori
Santa Cruz, CA