I brew in my apartment with two 2 gallon Mr. Beer fermenting kegs. Worried that the ambient air temp in my one story apartment is stalling the yeast (68-70F). I'm currently trying a warm water bath in a plastic tote with an aquarium heater set to 76 degrees. Is the upper 70's too high for the yeast?
I do not know what strain is in that Mr. Beer but I would be really surprised if 68F was cold enough to impede fermentation. I think 76F is more likely to be much too warm, and that can induce off flavors in your beer.
I agree with the rest, you should be looking at cooling the beer not making it warmer.
I ferment almost all of my beers at 66 degs. That is the temperature of the beer not ambient temp which is lower than that.