Jeff in Seattle
New Member
Hello,
I have a 3" sewer main with a number of branch waste lines that enter it. 3" lines are rated for 35 DFU maximum. I have added a few fixtures in my basement and elsewhere and am approaching the maximum DFU rating for my main. Recently, I was doing some careful calculation of every fixture and waste line that entered the sewer main. My question comes when you look at a DFU table where it states:
However, the table continues....
It should be noted that I have seen efficiency dishwasher units that you hook to the kitchen faucets. That would make sense to count the sink and dishwasher together since while the dishwasher is being used, the sink cannot. Kind of like the notation on diverters on shower heads versus multiple shower heads. Diverters do not add DFU since the water is going one way or another (not increasing the amount of water down the drain. While piped multiple heads beyond the first showerhead adds 1 DFU per (they can all be on at the same time increasing water down the drain).
Now, I just recently remodeled my kitchen. The UPC demands an air gap device for the dishwasher (not a high loop for the hose). This means you have to have a not so pretty air gap device on the sink (above the flood stage). During the remodel, my wife used up all 5 holes of the new sink with various fixtures leaving no room for the air gap. So, I bought a Johnston tee (an air gap device that can be used on the dishwasher as long as you are on an exterior wall (which I am). So the water discharges up the wall over the flood stage of the sink (this is where the Johnston Tee is installed with a vent on the exterior wall) then down to a wall trap which drains into the kitchen waste and vent line in the wall. This makes clearer sense to me for the standalone kitchen and dishwasher (each 2 DFUs) entries. BUT - depending on the answers from the original entry, does this still count as 2 DFUs?
YES, I know that all fixtures draining at the same time is near impossible and not practicable. Depending on this answer and some of the fixtures I might be installing, I might exceed the 35 DFUs (I am that close). I will likely have to up the sewer main to 4" in the last 10' before it exits the house crawlspace (which goes to a 4" sanitary ground line heading to the septic tank.
Thanks!
I have a 3" sewer main with a number of branch waste lines that enter it. 3" lines are rated for 35 DFU maximum. I have added a few fixtures in my basement and elsewhere and am approaching the maximum DFU rating for my main. Recently, I was doing some careful calculation of every fixture and waste line that entered the sewer main. My question comes when you look at a DFU table where it states:
- Kitchen sink, domestic, with or without food waste grinder and/or dishwasher: 2 DFUs
However, the table continues....
- Standalone Kitchen sinks: 2 DFUs
- Standalone Dishwashers: 2 DFUs
It should be noted that I have seen efficiency dishwasher units that you hook to the kitchen faucets. That would make sense to count the sink and dishwasher together since while the dishwasher is being used, the sink cannot. Kind of like the notation on diverters on shower heads versus multiple shower heads. Diverters do not add DFU since the water is going one way or another (not increasing the amount of water down the drain. While piped multiple heads beyond the first showerhead adds 1 DFU per (they can all be on at the same time increasing water down the drain).
Now, I just recently remodeled my kitchen. The UPC demands an air gap device for the dishwasher (not a high loop for the hose). This means you have to have a not so pretty air gap device on the sink (above the flood stage). During the remodel, my wife used up all 5 holes of the new sink with various fixtures leaving no room for the air gap. So, I bought a Johnston tee (an air gap device that can be used on the dishwasher as long as you are on an exterior wall (which I am). So the water discharges up the wall over the flood stage of the sink (this is where the Johnston Tee is installed with a vent on the exterior wall) then down to a wall trap which drains into the kitchen waste and vent line in the wall. This makes clearer sense to me for the standalone kitchen and dishwasher (each 2 DFUs) entries. BUT - depending on the answers from the original entry, does this still count as 2 DFUs?
YES, I know that all fixtures draining at the same time is near impossible and not practicable. Depending on this answer and some of the fixtures I might be installing, I might exceed the 35 DFUs (I am that close). I will likely have to up the sewer main to 4" in the last 10' before it exits the house crawlspace (which goes to a 4" sanitary ground line heading to the septic tank.
Thanks!