top of page

Properly Sizing your Whole House Carbon Filter when using a Tank System


Notice: It is critical that you properly size your carbon unit. To do this you will need to accurately determine the Maximum Service Flowrate (in GPM) of your incoming household water service to make sure your unit can properly clean itself during Backwash Mode.

You will also need to determine your Maximum Water Demand/Flowrate (in GPM) for your household, to make sure you have enough carbon to properly filter the water being used by several fixtures running all at the same time such as a shower, toilets flushing, 2 running sinks, and laundry machine etc.


Step 1: For standard Chlorine, Taste, and Odor removal, select your carbon unit by first carefully determining your anticipated Maximum Water Demand/Flowrate (in GPM) for your house. You must add up the water demand caused by several of your household's fixtures listed below. Under sizing a unit will lead to poor performance. This is measured in Gallons Per Minute.

Step 2: Next select a carbon filter system where it’s stated Maximum Service Flow is greater than the anticipated Maximum Water Demand/Flow-rate of your house.


Carbon works better with (more carbon=larger tank volumes), so you will get better quality water by having the Maximum Service Flow of the carbon filter exceed the Maximum Water Demand/Flowrate of your house by 2 or 3 or 4 GPM. Do not under-size your carbon filter or it will not work properly.


The Maximum Service Flow values given are for performing “standard dechlorinating”, which is relatively easy for carbon to do. For removing extra contaminants and organics (which is more difficult) you will want to subtract several gallons from that maximum service flow number – which will put you into a larger sized unit. More carbon means more contact with water, more contact time with water means better filtration.


Step 3: Make sure that your household water service can meet or exceed the Minimum Required Backwash Rate of the carbon filter you are contemplating. This is absolutely critical to flush out the collected sediments and properly clean the carbon bed. Over-sizing a unit so that you cannot deliver the Minimum Required Backwash Flow-rate needed by the unit will lead to carbon bed fouling and very poor performance.


If you have a lot of sediments in your water you may precede your carbon filter with a 20” sediment filter to keep the carbon bed and valves from fouling with sediments and rust. We recommend a 20” Big Blue which is considered high performance and creates the lowest pressure drop.


If you also have a water softener or water conditioner: Install the whole home filtration unit before (upstream of) the water softener to protect the water softener resin beads from chlorine damage extending the life of your softener.





Having some sort of filtration is substantially better than nothing at all. As long as you understand the system have a realistic expectation of what the system can do, it is properly maintained and installed you will end up very happy with the results and change in your water quality.

bottom of page