![]() Half of a 3” drain gives us 1.5”, and that’s the size of the stool’s vent. If your code is the IPC, then your toilet’s individual vent is sized at 1.5.”Īnd that’s because individual vents in the IPC are sized at no less than one-half the diameter of the drain served.Īs you know, the minimum drain size for a water closet is 3 inches. Wet areas near water connections, pump runs while the faucets are closed, and. For more information on the great importance of plumbing vents, read our plumbing vent article here.Īnd the size of this vent pipe depends on your local plumbing code. Luckily, there are some places that may have just. Here’s a question people ask sometimes… “Does a toilet need a vent?”Īnd the answer is yes, your toilet has to have a vent. The plumbing code does not consider a 4”x3” closet connection as a reduction in size…Īnd this fitting is a very wise choice under a 4 inch flange! However, there’s one exception (704.2)…and it’s with toilets. The plumbing code never allows a drain to be reduced in size in the direction of flow. It’s 4 inches on the inlet of the fitting and 3 inches on the outlet. Ive done it for years on many systems, even at my own home, and. This wet venting is permitted by most codes. The 3-inch pipe would never completely fill with water even if you filled the lavatory sink and pulled the stopper. This month we will dive into wet venting. The pipe that drains the lavatory sink is 3-inch in diameter because that drain line also acts as a vent for the toilet. *However, be careful in the UPC…(unlike the IPC), this code puts a limit on the total number of toilets allowed to discharge into a 3 inch drain. Only 3 total water closets are permitted to discharge into any 3 inch horizontal drain in the UPC.Īlso, check out the 4” x 3” closet bend below: In my last column, I reviewed circuit venting and the variations of it to which different codes allow. The UPC allows 35 DFUs on a 3 inch horizontal drain.The IPC allows 42 DFUs on a 3 inch building drain.Some older model toilets, flushing over 1.6 gallons per flush, are rated at 4 DFUs.Ī DFU is the unit of probable discharge that a particular plumbing fixture produces.Īnd drain pipes can only drain a certain number of DFUs.įor example, referring to the nifty table below you’ll find: The Only Fitting Code Allows for Vertical to Horizontal. Wet venting is limited to vertical drainage piping receiving the discharge from the trap arm of one and two fixture unit fixtures that also serves as a vent. Water closet’s flushing 1.6 gallons (or less) are rated at 3 DFUs (drainage fixture units). Wet areas near water connections, pump runs while the faucets are closed, and. The idea of horizontal wet venting was a later development and significantly differs from the group venting just explained. Regardless of your plumbing code, the minimum drain size for a toilet is 3 inches. ![]() But let’s dive deeper into this venting pattern and discuss… 3 things to understand before plumbing a toilet:
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