A few things on fermentation....
Airlock activity is not an indication of fermentation. Just because you don't see bubbles and a hear a gurgling airlock does not mean that your wine is not fermenting.
To take readings you need a hydrometer. A hydrometer measures a liquids gravity (or density). Liquid is more dense with sugar, and less with out. As yeast eats sugar and creates alcohol the gravity (or density) lowers.
When first making your wine you should have taken a gravity reading. Then, read it again week, 2 weeks, 3 weeks... whatever later and see how it's fermenting.
All of that being said yeast does not like sudden changes in temperature. It stresses them out and makes for unhealthy yeast. And unhealthy yeast makes for poor fermentation. If you want to warm them up then do it SLOWLY. Raise the ambient temperature of wherever you're fermenting by 1 degree a day. No more.
At what temperature are you fermenting? You really shouldn't need to be fermenting any higher than the 65 - 70 range.
I would advise against wrapping your carboy. Fermentation is an exothermic process. That means that it gives off heat. Inside your fermentation vessel it could be 5 - 10 degrees warmer than outside. Wrapping your vessel is a quick way to stress out the yeast as the vessel could heat up more on the inside than you intend.
Sorry for the book. Just wanted to be thorough.