The EM means emergency heat. It should be left off and only used when your heating does not work. You are using more power when it is on. Theoretically it should be able to heat your home but sometimes they don't.
Yes you should be able to heat your home without emergency heat if its designed correctly for it, if your emergency heat runs a little every now and then then it isn't so bad and there may be nothing wrong with your system but if its on all the time than you definitely have a problem with your system and need to have it looked at.