How much of a swing would the Democrats need to retake the house?

[Lurker]

As has been much discussed here, the Democrats will obviously have a hard time taking the House with the current district boundaries, particularly after the last redistricting.

I wonder whether anyone has looked into how big of a nationwide swing the Democrats would need (from the 2012 House elections) to get 218 seats and a majority in the House? I couldn't find any clear answer to this, but with this being the Atlas forum I'm sure someone has looked into it.

Would be interesting to see your estimates (or any definite numbers).