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.

Thanks in advance for any suggestions.

Paul