In your form you include the conductive loss calculation for the material
used to cover the house and a table of likely materials to help determine
its value. If you added the air infiltration heat loss calculation and a
table to help determine that value your form would be just like most of the
ones found online. Except yours DOES the calculation. Nice touch. :-)

I had a devil of a time remembering where I found my heating cost
calculation and had no luck making it turn up in google using any words a
person is likely to think of when trying to find the answer to 'how much
will it cost to heat my greenhouse this winter", then I typed in parts of
the calculation from my spread sheet that dealt with conductive heat loss
and the whole problem of determining heater *size* showed up on several
university websites that had hort or agriculture schools.

Some also had help/hints for figuring the extra steps needed to determine
fuel costs for a given period, not just minimum heater size for the coldest
possible temp on record, which is just the first step, really. Al-beit a
big one.

"Ray" wrote in message
news:qwdZg.3145$AR6.1801@trndny02...
...or alternately:
http://www.firstrays.com/heater_calculator.htm

--

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


"al" wrote in message
news:qmCYg.8416$6D3.5659@trnddc01...
I have been using the calculation supplied in the link below for about 8
years now. With it, greenhouse size info, data from local weather
stations, BTUs per unit of fuel and heater efficiency ratings I have been
able to determine not only how large a heater I needed to get me through
the coldest possible night I was likely to face but also what it costs in
fuel on any given time period of an average year. Once these numbers were
plugged into a spreadsheet and a running log of outside temps was recorded
it *did* provide a close approximation of the fuel actually used and
therefore I think it can be used to help you predict fuel costs.

But there are a lot of variables 'assumed' in this calculation. Like
wind speed. If possible locate your greenhouse in a way that protects it
from prevailing winds in your area. Windy locations will increase heat
loss through whatever covering you use and can swing the numbers wildly.
I am fortunate that my house stands between my greenhouse and the
prevailing winter winds.

http://aggie-horticulture.tamu.edu/G...hdbk/heat.html


Ed wrote:
OK, our 125+ mature orchids are overflowing our attached sunroom, so
we are considering a 10' x 12' polycarbonate greenhouse for the
backyard. I plan to keep my paphs and phrags as well as the Vandas
and warm types in the sunroom, but would like to move my phals, blc,
lc, dendrobiums, etc into the new greenhouse. We will be growing some
veggies and other plants in there as well.

I live in Lexington, Kentucky. Our winters are "fairly" moderate,
with some days in January or February sometimes into the 50's.
However, we also get a LOT of days below freezing, into the teens on
occasion. The coldest days also have the brightest sun. Very little
snow, maybe 6-8" a year. I am probably going to use electric heat as
well as heat cables for
propagation trays I have read several greenhouse books, but have found
nothing to pedict heating costs? My target is to keep night temps in
the greenhouse at 60 degrees.

I have no experience with greenhouse culture, so I could use all the
advise the group is willing to share.

Thanks,

Ed