Fortunately we do have relatively warm days. the majority of winter are for sure above 0C. on our super cold spells of -10C the days are rather cool, they don't last. for those short lived cold strikes, secondary heat like propane or something wont be bad as it will be temporary. I should maybe say, though it isnt fully accurate, that the heat inside an unheated greenhouse will probably be above freezing all but maybe 2 weeks a year (outside not, but inside yes). so the temp will *probably* only need raising say 10 degrees.
i have been reading about water systems, and air systems. for those interested this is an interesting website: http://www.sunnyjohn.com/indexpages/shcs.htm
it talks about using the ground as a heat sink, instead of water and using air and fans instead of water and pumps.
has anyone useds those portable oil radiant heat things sold in box stores? i had one a few years back in canada indoors. it had 600/900/1500 watt options which was nice, but doubt it could heat even a 20x20 kind of size.
using a low ball of 1500 watts for probably 24 hours a day during cold spells = 36KW. in my area 1kw=$0.09 (cdn) = $3.24/day = $97.2/month. that is -ok-, but a hundred bucks is a hundred bucks, and i really doubt that is enough juice to come close to heating a GH to 10C, never mind a standard 20x50' one... Has anyone heated a GH in cold weather with electric heaters? I am just not aware of how to calculate costs with propane type heaters, never used them. I am basing other energy costs from government studies on hot house productions, and wow that aint cheap. I will need at elast 1 20x50 as a bare minumim for my hot plants, but in reality should have 4 or 5 hot houses, then cool houses for veggies. I might sound cheap, but i want to have quite a few going, which is why i am trying to pinch pennies. that and the cost of living in BC is pretty darn high in my opinion, so just living aint cheap.
Stephen Robert Irwin: 22 February 1962 – 4 September 2006. Rest In Peace.