I have two 3 kw electric heaters so the two vents i am talking about are not
for this purpose,just for added ventilation to keep the air bouyant.My
greenhouse is pretty tight, its new and made from concrete block low walls
and solid wood draught proof double doors at one end and a 25mm
polycarbonate roof.It is probably too insulated as on a frosty day the
polycarb roof gets frosted on the outside and maintaining my 50 f inside !
Condensation can get bad though on the inside roof,so was thinking of
putting the two vents near the heater so the fan on them is drawing in fresh
air all the time .
So still undecided?
Keith
"Wendy7" wrote in message
...
Yikes! Interesting? Thanks for bringing this topic up Keith, I have
Southern Burners with
chimneys & a 2" air intake hole down under & 2 vents open. Seems like I am
wasting energy no?
I do have a up high that runs 24/7 to circulate the warm air but I was
under the impression
that there had to be incoming fresh air all the time.
Going to investigate.
Cheers Wendy

"alpickrel" wrote in message
...
On Dec 5, 6:46 pm, "keith kent" wrote:
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

I agree with Ray. (not that it matters but I frequently do) It would
be hard to suffocate in there. I estimate all the cracks and crevices
in my greenhouse are already equal to a square foot opening, ...at
least... and this does not include the vent flews/flues/flooze for the
heaters. I would have to have a hole in my head (its actually pretty
windy in there too) to actually add more holes to the greenhouse.

You can calculate a good guess as to how often the volume of air in
your greenhouse changes by calculating the air infiltration rate.
The air infiltration rate is one part of the calculation for BTU
requirements. Air infiltration and is based on the size and
construction material of the structure , among other less tangible
things like wind speed....
http://aggie-horticulture.tamu.edu/G...hdbk/heat.html
(See item #7 in the calculation)