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Rain Caps By Pipe Size

Pipe Size to Rain Cap Part Number Selection Table

We know its confusing when working between an exhaust pipe's NPS (Nominal Pipe Size) and the pipe size a rain cap fits. The source of the confusion is the NPS size and the pipe's outside diameter (OD) - they don't refer to the same size. For example, a 4 inch NPS pipe has an actual outside pipe diameter of 4.5 inches. Confused? Don't feel still confuses us! So we created a table that eliminates the confusion and provided it for you to use below.

Table Instructions:

  1. Locate the NPS size of your exhaust pipe in the first column, titled: Nominal Pipe Size. It does not matter the Schedule of the exhaust pipe you are using. All Schedules (10, 20, 40, 40S, 80, 120, HD, etc.) of that NPS have the same Outside Diameter (OD). They have different wall thicknesses and inside diameters (ID) but always the same outside diameter.
  2. Verify you have the correct Nominal Pipe Size selected by measuring the actual outside diameter of your exhaust pipe and compare it to the 2nd column, titled: Pipe Outside Diameter (inches).
  3. Staying on the same row as your exhaust pipe's nominal pipe size, select the material and finish your application requires from the 3rd, 4th, 5th or 6th columns. Click on the rain cap type's part number to take you to the specifications and price. This is the rain cap that will fit your exhaust pipe.
Nominal Pipe Size (NPS)Pipe Outside Diameter (inches)Steel Rain CapsAluminum Rain CapsStainless Steel Rain Caps