If you need to replace your hot tub filter but aren't sure which one you need then you're in the right place! In this article, we will walk you through the proper way to find the right replacement filter for your hot tub. But first, why do hot tub filters need to be replaced anyway?

Why Do Hot Tub Filters Need To Be Replaced?

Hot tub filters are made up of several layers of woven paper webs stacked on one another. Water is allowed to pass through the tiny holes between these webs while dirt and debris are trapped.

Over time, these webs begin to break down and get looser; allowing larger and larger debris to pass through them. Eventually the filters are no longer able to effectively filter the water and need to be replaced.

How To Measure For A New Hot Tub Filter

Check For A Model Number

The first step when replacing your hot tub filter is to look to see if it has a model number on it. This will typically be moulded into the plastic on the top of the filter and will be a combination of letters and numbers; something like C-4950 or PRB50-IN.

A hot tub filter with the model number visible (bottom).

Measuring The Length and Width

If you can't find a model number, or if you can't find a replacement filter with that same model number, it's time to start measuring!

Start by measuring the width of the filter at the widest point of the top cap. Next, measure the length of the filter, ignoring any threaded ends or handles that might protrude past the end caps of the filter.

Note: There is commonly a difference of around 1/16" between different filters of the same model. If you measure the width of your filter at 4-7/8" and the replacement filter is listed at 4-15/16", you've probably still got the right filter.

Measuring The End Caps

Once you've measured the length and width of your hot tub filter, you then have to determine which style of end caps it has. The most common end cap style is the "open top" filter. This filter has a hole in the centre of the filter that extends all the way through the filter. If you have an open top filter, simply measure the width of the centre hole. Most open filters will have a width of either 1-1/2" or 2".

Threaded Filters

Another common end cap configuration for hot tub filters is the "closed top" filter. This type of filter is closed on the top and has a threaded end on the bottom. These threads come in two types; SAE (course thread) and MPT (fine thread). Measure the width of the opening in the centre of the thread end (excluding the width of the threads themselves) and note which thread type you have.

Other Types Of End Caps

While the vast majority of hot tub filters come with either the standard open or closed end cap configuration, there are some hot tubs that use specialty end caps that differ from these standards. While they may look different from standard hot tub filters, these filters are measured in much the same way as standard filters, and can usually be picked out simply by eye. Consult the image below for a list different possible end cap configurations.

How Long Do Hot Tub Filters Last?

When properly cared for, hot tub filters should last for 12-16 months, depending on how often the hot tub is used. Filters that are not properly cared for need to be replaced much more often, usually every 6 months.

To make sure you get the full life out of your new hot tub filter, take your filter out every 1-2 weeks and spray it off with a garden hose to remove trapped dirt and debris. Once every 3-4 months, chemically clean the filter using something like Eco One's Spa Filter Cleaner or Pleatco’s Spa Filter Wash Tablet to remove built up oils and lotions.