Tough situation....I'll give you my experience and I hope it helps you in some way....

I was a joint a day smoker for 10 years.....I was starting to get a chest infections, got colds all the time, my health was suffering but I didn't wanna stop doing it, despite the risks....then I found forums like these and it changed my life....since I started using the Herbalaire vaporizer a year ago, I very rarely get colds, no chest infections, no cough, I have better endurance when I play hockey, my chest isn't tight all the time....the only trade off for me is that to truly get the health benefits out of the vaporizer, I can't get the full body stone....I miss it but I don't want to turn the temperature up too much or I may as well be smoking it....it has it's advantages though....you can still do stuff and not feel like crashing....great for the daytime cause you still have lots of energy to get stuff done....not as great at night if you wanna chill....depends on the strain though.
I've smoked a couple with friends and it is NAAAAAASTY....can't stand the taste and smell of smoke anymore....it didn't take long to feel that way either, maybe a month....anyways, all I can say is that it's allowed me to continue my love affair with MJ (don't tell my wife) and do it so that there is as little damage to my body as possible.....good luck to you!

Oh and to answer your question, they use very little, maybe .2Grams to get you wrecked.....it's maybe about a bowl or a litle less.