Question: Why is this を and not に to indicate moving in a direction?

```
今日は天気がいいから家を出ます

```

Unless this example is wrong? But it is from JapanesePod101

Answer: 
出る is not a normal motion verb.

> 
> Xに出る
> 
> 
> 

means to participate in X.

For example, カタン大会に出る would mean to participate in a Settlers of Catan tournament.

> 
> を出る
> 
> 
> 

means to leave a place. 　see [Differences between 出るand 去る when expressing someone leaving](https://japanese.stackexchange.com/questions/5645/differences-between-%E5%87%BA%E3%82%8Band-%E5%8E%BB%E3%82%8B-when-expressing-someone-leaving)

[Why does 出る accepts を although it is an intransitive verb?](https://japanese.stackexchange.com/questions/21313/why-does-%E5%87%BA%E3%82%8B-accepts-%E3%82%92-although-it-is-an-intransitive-verb/21321#21321)
Because it is not moving "in" a direction. It is moving "from" somewhere, since I suppose someone is going out "from" the house.

In general 出る follows either を or から. There are cases in which you are actually referring to "going out towards some place/situation" in a more figurative way or with the meaning of "to participate" in which you can actually use "に". For example:旅に出る, or 社会へ出る, and others.

By the way, your example feels a bit weird to me, as I would rather say: 今日は天気が良いから、家を出る。I feel there is a missing connection between 良い and the next sentence 家を出る. Maybe even just changing to 良くて would be enough.

Anyway, you can find a detailed explanation on 出る [here](http://dictionary.goo.ne.jp/jn/152769/meaning/m0u/) and some explanations and example on when to use を or から [here](http://www.alc.co.jp/jpn/article/faq/03/221.html) (for example there is a difference whether you are talking of a concrete movement or not and so on).