Depends on your heater also.
For electric systems there are two common methods IIRC, one of which involves basically heating a coil of sorts (think of a space heater on a larger scale) and then blowing air over it and into the home, this method is very inefficient and cost a lot to do but produces more heat faster, a lot of times this method will be referred to as "emergency heat" on systems that have both methods. The other method is slower to get the temp to what you want but basically reverses the method the AC unit does to cool the home down and uses a lot less energy.
I'm no expert but this is how it was explained to me awhile ago.