Where to Find and Catch Heatran
From Pokemon Go Wiki
Heatran are found and captured in Nest and Habitat locations.
Nests
Heatran Nests are locations that consistently spawn Heatran.
Habitats
Heatran Habitats are spawn locations where Heatran is likely to be encountered, but not guaranteed the way a Nest is.
Additional Tips and Information
Best Nests
If you know a really good nest or any of the nests above is really good, list them here: