Washer drains

Right now the existing drain line from the house is 4" in diameter.Would that size drain line be able to accomodate the capacity of draining water from two washers? It would be fairly safe to think the waherswill not be running at the same time.If more information is needed please ask this is what i know about the drain there at this point.

Thanks all

Not only will you likely never drain both washers at the same precise time, even if you managed to the 4" drain will handle it. The old high school geometry formula for the area of a circle, PI x radius squared tell us that the area of a 4" pipe is 12.56 square inches. The area of a single 2" drain is 3.14 square inches so the the combined area of both 2" drains is 6.28 square inches. The 4" drain then has twice the capacity of what both washers could put out at one time.

Washing Machine Drains

Yeah But Gary You Left All The Other Fixtures In This House ! !
Is This House Split Into A Duplex ?
2 Kitchens Etc.

What do suppose? Will every drain in the whole house be dumping full bore all at one time? Even then, you have half the area of the 4" drain available.

A 4" horizontal line properly pitched has a capacity of about 130-140 Gallons Per Minute off the top of my head...

Thanks, Redwood. Your answer gets us out of the math textbook and into practicality. Bottom line: A 4" drain is large enough to handle any amount of water even a large household could possible put in to it.

Thanks all for the great replys!

Yep, Gary that old high school geometry formula popped in my thoughts to 3.14XR2.. Was just figuring code might require some weird extra addages for just in cases that might happen once every 10 paleozoic years..

Thanks all!

I don't have the book in front of me right now to quote numbers, but drains are designed using what are called "DFU's"....drainage fixture units.

It goes something like this: a lav sink is a 1, tub 2, toilet 3, clothes washer 3, etc. So all the DFU's are added up. A 4" pipe has a DFU rating of about 200, so you are not even close to max'd out.

I think the ratings are based on an assumed random loading. I think for example a laundromat where it could be assumed that all machines are running together, they have to do some calculations bases on gallons per minute total.