Acts 20:17-20 Paul is not discussing preaching to unbelievers but rather teaching those who already were Christians. He says;
"However, from Mi·le´tus he sent to Eph´e·sus and called for the older men of the congregation. 18 When they got to him he said to them: "YOU well know how from the first day that I stepped into the [district of] Asia I was with you the whole time, 19 slaving for the Lord with the greatest lowliness of mind and tears and trials that befell me by the plots of the Jews; 20 while I did not hold back from telling YOU any of the things that were profitable nor from teaching YOU publicly and from house to house."
A more accurate way to understand these scriptures in Acts is "we were teaching you at your homes" similar to the way Witnesses hold congregation book studies. Paul here relates his past activity in teaching "the older men of the congregation" privately within Christian homes. Early Christians did not have Churches but met in homes, and it is to this that Paul was referring.
Not only that (great post btw, jwfacts) but the contextual background to this shows that Paul and others didn't go "from house to house" in the way JWs argue.
- Acts 18:19-21 - Upon his first arrival, Paul preached in the synagogue;
- Acts 18:24-26 - New disciple Apollos preached boldly in the synagogue; more experienced Priscilla and Aquila invited him to their private home to teach him further;
- Acts 19:1ff. - Upon his next visit, Paul sought out believers.
- Acts 19:8ff. - Paul spent 3 months teaching in the synagogue which ticked off the unbelieving Jews; he then had daily discussions with the new disciples in Tyrannus' lecture hall which, during those two years, attracted both Jews and Greeks from nearly all the Asian province (cf. Acts 19:26).
No mention of going consecutively "from house to house" as a preaching method.