I'm probably the last person to ask about incubating duck eggs as this was my first hatch, but my temps were @ 101-102 intermittently HOWEVER, for the first 2 weeks, the eggs were set by my Silkie, who finally abandoned them.
I then ran them into the house as they were ice cold and rigged up this silly incubator consisting of only a human heating pad, a clear plastic small animal carrier, Saran Wrap (to keep in humidity), a couple of towels (one under the 'bator, one on top of the Saran Wrap on top of the bator), a digital thermometer/hygrometer, and 2 small container of water with about 4 inches of cut sponge sticking out (for greater surface area to raise humidity). Hoo, boy, I will NEVER do that again! Lol. But, I was able to keep humidity at about 50-55 for the majority of the duration by misting the eggs about once a day, and keeping the water containers filled. When they pipped, I got the humidity up to 65-75% by very carefully misting the inside wall of the bator. Trust me, using this emergency bator was an absolute nightmare, and it is only by sheer miracle they made it, I swear. If I wasn't a stay at home mom, they probably would have either froze to death or burned up if I weren't checking temps all the time!
I'd ask about specific humidities in the duck section of this forum, to people who actually know what they're doing, lol.
But good luck! I'll be building my own bator really soon!
Just before the final push:
The breech baby...you can see there is still a little blood, I could have/probably should have waited until this evening before rupturing any more membrane, but experience is the best teacher! I have only hatched out reptiles (many years ago). Never done this before...but we're done with it now!