Q. Can you smoke electronic cigarettes on Pesach (Chol Hamoed)?

A. An electronic cigarette or e-cigarette is a handheld electronic device which vaporizes a flavored liquid. The user inhales the vapor. Using e-cigarettes is sometimes called vaping. The liquid in the e-cigarette, called is usually made of nicotine, propylene glycol, glycerine, and flavorings. (Wikipedia)
Mishna Berura (467: 33) quoting Magen Avrohom and Chayei Adam prohibits smelling “tabak” that was steeped in beer.
However, traditionally people are lenient in smoking on Pesach common rolled cigarettes or pipe tobacco, since even if chametz was mixed in the tobacco, it is inedible, and smoking it does not constitute “achshevei” or making it important. (see Sdei Chemed 1: 3, Tiferes Yosef O.H. 26, Mor Uketziah end of 442, Chaim Shoal 2:38 sec. 83, Ha-Elef Lecha Shlomo 204-205; Divrei Chaim Yoreh Deah 20 – and others).
CRC published in their site the following alert: “Electronic cigarettes convert a specially formulated liquid into a vapor which the person inhales in a manner that mimics the way one inhales from a traditional cigarette. The liquid (which is sometimes called “juice”, “smoke-juice” or similar names) typically includes kosher-sensitive ingredients such as glycerin and flavors, and since the person imbibes the liquid/vapor, Rav Schwartz said that the liquid must be certified as kosher. We contacted a number of manufacturers who claim to use only kosher raw materials but there is no independent agency who certifies that claim, and therefore we are unable to recommend those products. [As with all medical issues, one should consult with their doctor before deciding to use or not use electronic cigarettes.]”
The Talmud (Avodah Zara 66b) discusses the use of a bas tiha, which is a straw-like tube (see Tosafos Ibid) introduced into a barrel of wine and used to inhale via the mouth the vapors of non-kosher wine in order to determine whether the wine is satisfactory. Rava, permits because reicha lav milsa or scent is nothing. Shulchan Aruch (Y.D.108:) rules leniently.
Piskei Teshuvos (467: 9) quotes different opinions in regards to smoking in Pesach, but concludes that kosher certification is needed for cigarettes or tobacco that may contain chometz.
Horav Shlomo Miller’s Shlit’a opinion is to be stringent unless one knows that the ingredients of the liquid in the e-cigarretes are not chometz. It is different than the “bas tiha” above, since the smoker enjoys the vapors he absorbs in his mouth.

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit’a