Non-heritable effects (including epigenetic) are estimated to contribute to less than 30% of population intelligence variance.
For instance, we could say that the heritability of intelligence among the children of suburban Chicago families in a particular income bracket is 70%, but not that the heritability of intelligence in general is 70%.
The most informative studies in this area are usually of twins-separated-at-birth, but the datasets aren't very large.