How far can a main vent pipe run horizontally

I have put in a downstairs bathroom. It is a remodel job in my house. I haven't done much of this kind of work. I have a problem trying to get the main vent up and out. If I could run it horizontally for 20 feet then up I could make it work. Any ideas?

vent

The way you ask the question it would be okay, but there could be other factors you are not telling us that would preclude installing it that way.

What do you need to know? This is a bathroom I made by dugging out a crawl space. Its in a corner of the basement I have the vent pipe up through the bathroom floor but because the house is finished upstair I am trying to find a wall that I can make enough room to get the main vent pipe through its a 4" pipe. Iam finishing a small addition that I could go up through but its 20' from the pipe I have up.

vent

As long as you are not using an existing drain pipe for the vent it can offset wherever necessary, but in your installation a 2" vent may be all you need.

A vent can be 1/3 the distance horizontal to 2/3 vertical.

If you have more horizontal than this, you can go up one pipe size.
Most bathroom sets that include a toilet only require a 2" pipe, so if the horizontal is too far, then the next size up would be 3".
You may check with the inspector though, he may consider the 20' okay.

UPC code 904.2

http://www.iapmo.org/common/ROP2004/upc04rop/preprint/ch9.pdf

Thanks for the help This is really a great site. The best i have seen. You have some great answers for alot of problems. Thanks again.