"Kay Easton" wrote in message
...
In article , Franz Heymann notfranz.
writes

"Ramon A" wrote in message
...
Plan to use a gas (propane) heater in an Alton Amateur Wood greenhouse.
I
Understand i must ventilate top and bottom with a minimum (33 square
inches)
vent. Plan to do the bottom vent in wood panel at the foot of the door

I think best place for the apex vent is prolly opposite the door
replacing
the 2 small top glass triangular panels .

BUT, any ideas how i can vent at the apex and minimise heat loss at the
same
time?

There is no such thing as ventilating without heat loss.

But you could get the loss to a very low level by a heat exchange
system. Seems a bit over-elaborate for a greenhouse though ;-)

True enough, but I have never seen a greenhouse application of that
principle. I did once design such a system for minimising the heat gain in
a
liquid hydrogen container.

Franz