Hello. I have constructed a very small-lean to 'greenhouse' against the wall of my garage. The size is: 6ft high x 3 ft wide x 15 inchs deep (very small, but all that the situation will allow.) The front is a double door and there are 4 shelves on drawer runners so that they can be withdrawn for easy access to the contents. The bottom 2 ft is T&G timber, the rest is glazed in twin wall poly. I have had great success this year in sowing seeds and taking cuttings in it but I would now like to put a little heat into it to overwinter some cuttings. I just want it frost free and my thought is to drill a hole through the garage wall to feed a cable to the nearest socket, and run a tubular heater in the lean-to itself. My question is what rating of tubular heater would be adequate for 22 cubic feet? They range in size but my favoured option is the 1ft long, 60 watt job which is of course the cheapest to run. Do people think this would be adequate to keep the inside frost free or should i put in a higher wattage?

Thank you for reading this.

JD