I'm looking for an electric greenhouse heater, predominantly for frost
protection over winter. There are obviously lots available but most
that I've seen have only a vague setting for frost protection - it's
usually just a rather uncertain position on a continuously variable
control knob. And just a tiny adjustment either up or down seems to
make a major difference to when the heater comes on. There's obviously
a temptation to set it on the high side 'just to be safe' but the
result inevitably is an expensive waste of electric power.

What I'd like to find is a model that has a more accurate temperature
calibration, ideally one that has eg a positive click position just
for frost protection or alternatively one that has an accurate
temperature scale marked clearly in steps of eg 1-2 degrees so that
there is little ambiguity about exactly what temperature it should
come on at.

Anyone have any receommendation for a suitable make/model please,
preferably without spending a fortune. The greenhouse is 8x6 so the
power output doesn't need to be enormous.

TIA
John Dann