View Full Version : 3" Mains?

10-29-2008, 04:10 PM
Just read an article in PM, advocating nothing larger than 3" for all vertical and horizontal mains, including the run out to the tank or sewer. The authors reasoning is that with low flush toilets and the new HET's there is so little water mixed with the poo that for separation not to occur, smaller pipe sizes should be used. Not sure how I feel about this, but I'd like to see some data. (none was supplied unfortunatly)

10-29-2008, 04:16 PM
This is a subject which has been debated and studied to death, including in engineering forums like PM Engineer. I don't know if there is a "final answer" right now. IAPMO is also studying the issue with regard to code requirements.

Another issue under study is possibly reducing the size of the hot water supply to bathrooms. With everything low to very low flow, a lot of heat loss energy and water down the drain could be saved with smaller pipes, and possibly little or no effect on flow to the shower. Film at 11:00

10-29-2008, 06:07 PM
Most of the studies show that the drain line carry for toilets improves with the smaller 3" pipe verses the larger 4".