Should I put an article before "House E"?

When you say "house 25", you don't add "the". Does the zero article apply to the use of the alphabet: house e?

When an ordinal number, or letter functioning as such a number, follows a noun, the article typically should not be used. I think this is because really what is happening is that the number is actually functioning as a noun and the preceding word is technically a modifier - because it's possible to omit the preceding word.

Right now I'm on step 16 (or it could be "Right now I'm on 16" if the listener knew you were working off a list of steps)

I've parked in space 'F' (again, "I've parked in 'E'" will work, if the listener knew you were trying to find a parking spot)

So, for:

I'm looking for house 'E'.

don't use the article.

Of course, with something like:

I'm looking for the 3rd house.

you would use it.