What should I do about a black bird nest on top of a heating vent?

Hello,

I spotted that a black bird has built her nest on top of a heating vent of my neighbours house. I knocked to let them know but no answer. I'm going try again, but I'm not even sure what to suggest to my neighbour in this situation?

Would heat/steam from the vent definitely harm the nest/nestlings? Is it reasonable to suggest to my neighbours to avoid using the vent while she is nesting? If they chose not too and kill the chicks - is it considered deliberate? 

I checked and there are no eggs in the nest yet. If my neighbours are unable to stop using the vent - would it be best to move the nest before eggs are laid?

Last year a cat destroyed the blackbirds nest and ate the chicks.  I'd hate to see this year's nest be cooked on a heat vent Disappointed

Any suggestions would be greatly appreciated. 

Cheers.