Evaporation of water from a flask, especially an Erlenmeyer, would be among the least of your worries. You would need to be certain that the cooker hood is safe for flammable solvents like heptane. Presumably it has a brushless motor?
And doesn't vent anywhere inopportune?
Using the pertinent data you could form the basis of a safety check by calculating the maximum vapour concentration of heptane that will pass through the cooker hood - something that's safer to slightly overestimate. Compare this with the explosive limits of heptane (which is what minimum or maximum concentration of it in air explodes when ignited - there is an upper as well as a lower limit and it is the lower one that is important here).
Relevant anecdote here is that back in the 1970's some guys in a pathology lab were evaporating ether from some faecal specimens, next to a fan in the ground floor window when some poor unfortunate soul chose to light a cigarette outside. Cue joke about the sh*t hitting the fan... True story though.
Fortunately, heptane is way less flammable than diethyl ether both in terms of volatility and the ignition temperature.
βThere is a way of manipulating matter and energy so as to produce what modern scientists call 'a field of force'. The field acts on the observer and puts him in a privileged position vis-Γ -vis the universe. From this position he has access to the realities which are ordinarily hidden from us by time and space, matter and energy. This is what we call the Great Work."
β Jacques Bergier, quoting Fulcanelli