On Sun, 03 Jan 2010 09:42:56 -0500, Phisherman
wrote:

On Wed, 30 Dec 2009 07:00:30 -0800 (PST), Pavel314
wrote:

Just to clarify the question, here's my original post to the home
improvement group:


We have a small greenhouse attached to the south side of our home.
It's 14' X 12' with a shed roof tapering from 10' on the house side
to
6'. Roughly 1,400 cubic feet. It's a 2x4 frame with double-walled
polycarbonate sheeting, 10mm for the roof and 6mm for the sides.
We're
in Maryland, near Baltimore, so it rarely gets below the mid-teens in
the winter.

We heat it with a 220V electric heater, 5,600 watts and 19,110 BTUh
rating. This generally keeps it at the 50 degrees the plants require
but occasionally my wife puts on a 110V supplimental heater on cold
nights.

The power hasn't failed in the winter since we got the greenhouse but
it's probably only a matter of time. I was thinking of getting a
kerosene heater as back-up to the electrical heaters. Home Depot has
a
23,000 BTU heater for $129 which seems to fit our needs. Could I use
home heating oil for this or would it be better to stick with pure
kerosene?

I was wondering about a propane heater; would that be more efficient
than kerosene? We have a propane ball/tank for some other
applications
which aren't used in the winter.


Paul


Some plants will refuse to bloom or struggle with growth if there is
too much propane, natural gas, or petroleum vapors in the air.

That would depend on concentrations, heating a greenhouse would never
reach such concentrations due to the fact that rarely are greenhouses
anywhere near airtight.

Electric heating makes more sense, safer, cleaner and expensive.

True, electric heating is typically expensive.

Kerosene heaters are not recommended due to increase of fire risk.

Kerosene space heaters are never safe, they also pump soot into the
air.

Gas is typically the least costly fuel and as to fumes from combustion
there is no reason that combustion needs to take place inside the
greenhouse... a gas hot water heater can be placed outside with hot
water baseboard piped in, with a thermostatically controlled
circulator. Which fuel to choose is primarilly based on climate, in
warm climes where heat is needed only occasionally then inexpensive
electric heaters may be the way to go but in colder climes the cost of
a gas heater will quickly pay for itself.