Where are you located? Ducks don't need heat unless you live next door to me in central Alberta Canada where we can get to -34C..
My Friend up North of me has that heat source for her Chickens.
Well I believe they are for indoor use and a GFI cord should be used also. I have little Call Ducks and I don't do anything for them till the temp drops below-25C they have deep straw and covered Run plus a Dog house. I'm moving them into my Chicken Coop that houses my Rabbit and bunnies as soon as the Bunnies leave. I won't use heat though.I live in northern Colorado. It gets below freezing, snow etc, a regular winter...however we will have warm days above freezing commonly. I was thinking maybe putting it outside the coop in a protected corner?