"jinty3319" johnunderscoredolan3319atyahoo.co.uk wrote in message
...

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be withdrawn for easy access to the contents.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




--
jinty3319

It isnt that simple!
IMO you cannot guesstimate the size of heater from cubic capacity, it
depends on the amount of heat you loose, and heating engineers that
calculate this still have to guess a bit. The old way of doing it was to
calculate the heat loss, a function of the temperature drop and a thing
called a U value which was worked out in a lab, and then doubled for good
measure (guess a bit!).

Depending on where you are, how exposed it is, hw warm the wall it is
attached to, and the ubiqitous moisture content of the air, 60 watts should
be more than enough for a space this small..............BUT

I thonk you would be best doing a few experiments, measuring the inside and
outside temperature, with and without heat.

Perhaps a thermostat might be a good idea after you have done the
experiments

You might be able to find a thermograph on ebay, if not you need max min
thermometers, you will need two, one in the greenhouse and one outside, to
do your heat loss eperiment.

This could all get very complex for a diddy greenhouse unless you are very
keen to get it to work.

Good luck!

John