To be franks hatching eggs without incubator is not adopted. There are many basis for it. It is not only the temperature which is significant in the total procedure of hatching but also the take charge of incubation RH that is vital. But, these days many public are attempting to experiment on some uncommon ways to induce the ducks eggs.
The most sought after procedures to heat duck eggs without using incubator, is by installing the lamp below the lamp. On the other hand, you should make sure that the egg is not placed straight under the lamp, also, you have to rotate the sides of the eggs every four-five hours to avoid concentration of set alight on particular side only.  Additionally, you have to ensure that you sprit the duck egg with water at least double a day.  
Then there is a procedure called natural incubation. In this, you can easily place the duck eggs under a broody duck. Muscovy ducks are considered as the best egg setters and these have the capacity of hatching 12-16 eggs. But, you have to secure that nest box should be located in the dry and clean prtotection, bedded with advisable litter. There must be adequate amount of water and feed ready for the broody duck and fake for the ducklings when they breed.
At last, we have to know the reality that there is a extreme difference between eggs hatched by incubator and eggs hatched by other procedures. Incubator does not provide only heat to the eggs, they are many other ways which can keep eggs at 80-90 degree Celsius, but it is also the moist which is controlled in the incubator. If wetness is not there the chick may get ashore on the side of the egg and may in the end die before present hatching. Public do attempt different procedures for hatching, but only some of them attain excellent outcome. Incubator is safe and is also not very excessive that it could burn a hole in you pocket. Hence, it is desirable to go for incubator.

Recommended Reading

• ducks