Average temps for the next 3 months in my area are around 7-8°C (45°F) min, 15-16°C (60°F) max.How cold is cold? Whats your average day and night temps over there?
I mean if its cold then a 600w hps will light up a 1m x 1m tent really well. Since your growing autos you have less or no dark time to worry about heating the space. Use your QB when winter is over.
Heat can be a good thing. Sometimes we forget that in the pursuit of efficiency
I might just do that... financially it looks like it's about my only option at the moment to beef things up somewhat. If it's too hot just with the HPS, I'll make do with the QB for full grow cycle and maybe just put the HPS on lowest dim setting to supplement at Flowering.