installing wood stove vent pipe to exterior

[effi]

can the vent run horizontally or vertically out of the house? is one preferred over the other?

[George E. Cawthon]

By vent pipe, I assume you mean the smoke outlet. Pipe can run horizontally (actually should be at a slight angle up) and can exit horizontally but the last sections have to be vertical. Straight up is preferred, horizontal sections should be relatively short. Local code may say differently.