I find that no matter how "tight" you think the GH is, there is enough
leakage to keep fresh air exchange going, so adding all-the-time vents is a
waste.

Don't forget: nature hates a gradient. If the air chemistry changes
inside, Mother Nature will remedy that insult.

--

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


"keith kent" wrote in message
...
What do other orchid growers do ?Do you shut up the greenhouse and use
fans internally 24/7.This is what i do ,but i am thinking of installing
(adding to this) two 100cm round core vents at low level at each end of
the greenhouse grilled on each side so they will be permanently open to
introduce fresh are.Now i am thinking will this be beneficial and will it
effect heating costs/heat loss .
Thanks Keith