preheat on what thickness coupon?
Mild steel or some exotic high strength alloy?
for 3/8" mild steel, I'd say no heat required as long as it's above 32°F, if not 32°F, bring it up to 70°F before welding.
However, I still like to see them cook off any cutting oils or whatnot by waving a torch over the groove and wire brushing before starting in on the root pass.