Democrats need to flip at least 24 seats to take back control of the House. My prediction suggests that they will gain some seats, but not sure if they could reach over 23 seats. According to my model, their gain is somewhere in the range of 5 to 23.
Here, take a look at the Competitive Districts, Hillary land (Districts represented by a Rep & Won by Hillary Clinton in 2016), Trump Job Approval by different pollsters, some historical data, including Presidents Job Approval, Generic Congressional Vote & number of seats gained/lost by Democratic Party in mid-term elections since 1994 & finally number of seats (gain/lose) by the President’s party based on my model(s).
Full Analysis in my GitHub Repository.