What is a DFU? Are they important?
The plumbing term DFU stands for drainage fixture unit. A DFU is a a measure of the probable discharge into the drainage system by various types of plumbing fixtures. The drainage fixture-unit value for a particular fixture depends on its volume rate of drainage discharge, on the time duration of a single drainage operation and on the average time between successive operations.
As seen in the chart above, one drainage fixture unit is equivalent to one cubic foot of water drained into a 1-1/4″ pipe over a one minute period of time. In order to keep the drain system flowing properly it must flow the proper amount of DFU’s, otherwise the drainage system will not drain properly. Common symptoms of insufficient DFU’s include:
- drains gurgling
- slow drains
- clogged drains
- dry p-traps
- dry s-traps
- sewer smell and odor
Plumbing Re-Pipes & DFU’s
If you need to have your plumbing replaced it is critical that sizing is correct for drainage fixture units. A drain pipe is will only carry so much water per minute. Ideally the water inside of the drain pipe will only fill the bottom third of the pipe. This arrangement allows for air to freely move through the top two-thirds of the pipe. A properly vented plumbing system will be a properly functioning plumbing system.
One of the beautiful parts of the Uniform Plumbing Code is that it protects the drainage system so well. Unlike the International Plumbing Code, the UPC requires every fixture to have a vent. When you have the DFU’s correct throughout the system you will not have issues with traps going dry.
When there are not enough drainage fixture units then the system can actually pull water from a trap in an attempt to get air. This can create a dangerous situation wherein poisonous sewer gases can enter the home. Sewer gasses can make your family sick and spread disease. During the Chinese SARS outbreak in 2002-2003, it was found that dry traps led to spread the virus.
We do it the right way, not the easy way
When you call our team of Comfort Heroes you can rest assured that our licensed plumbers will do the job right. We have decades of experience and our staff is always ready to serve you at the highest level. If you would like to schedule an appointment to have your drains looked at then call us at [hls_phone_number].
