Polyhouse heating for Orchids

[kaarthiik]

Hi Guys,

Need your inputs on getting a good heating equipment.
I stay in a area where I do not get frost but the minimum temperature touches 3 to 4 C for a week during nights. Average lowest temperatures would be 6 to 10 C during nights and upto 18 C during days of winter.

I am growing orchids in a mini poly house of 8 Feet wide 4 feet deep and 8 feet height. For ventilation, I keep the entry curtain open for ventilation. Sun would be direct on greenhouse from 10 AM to 1 PM approx.

I am growing Phals, miltonias, catts, Vandas, Rhycostlis, Dends, Gramatophylums Paphs and HTC Cymbs. And few other Anthuriums.

Now please guide me how to get a heating set up for winter.
Use 2KW common blower on 1 KW settting controlled by a thermostat?
OR
Use a Halogen heater with 3 rods (400W each) with one or two switched on?
OR
Use a tubular heater with the thermostat setting of 120 W (3 feet or 4 feet)
Or
Use 200W frost control heater .. seen on EBay claiming it is similar to 4 feet tubular heater on functionality.

Please guide me, or any other better idea if you have please share.