Or you can use a heat pad for reptiles under the iso to evaporate it,something like this
http://www.ebay.com/itm/HEAT-MAT-Terrarium-10-20-Gall-Under-Mount-Reptile-Heater-/281669874119?pt=LH_DefaultDomain_0&hash=item4194d531c7
always be carefull when u use fire with alcohol of course its...