Al,

I got around the heater-related issues by buying a separated-combustion
heater.

Combustion air is drawn in via a 3" flue from the outside. That actually
runs inside of the 6" exhaust flue, which is sealed through the back GH
wall. The cold, outside air is preheated by the exhaust, which increases
fuel combustion efficiency.

All of the controls and the burner are in a sealed volume, so I don't suck
the heat or humidity out!

But then there's the door....

--

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


"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)