Im almost sure yes, as the weight of hash oil i usually get is about 1/10th of the weight of the weed i start with. Well... i dont know. I never did a sucessfull butane extraction (i tried it once but the weather here where i live is way too hot), so i cant compare it with the other solvents. If i remember rightly, the butanes boiling point is around 40F, so it would take a lot of time to evaporate. It would help a lot the extraction process, as the weed would be soaking in the liquid butane for a longer time, allowing a more effective extraction. I would suggest you to do the extraction outside, until you fill the pyrex glass with the liquid butane+oil, then go to a warmer place to evaporate it. Just remember to evaporate it in a place far away from heat sources, sparks, flames, cigarretes, or anything that could ignite the butane fumes, as it is VERY flammable and could easily cause a fire or an explosion.