Why the Air Box 4 Plus Refill Cartridge Is a Different Part
The 4+ uses an XL cartridge that no other Air Box takes. It measures 16 x 24 x 1.5 in, half an inch thicker than the standard cartridge. The housing carries four of them behind a 12 in flange rated to 3500 CFM. That extra depth is what holds contact time at the far higher airflow this unit passes. Media is 100% activated charcoal from premium virgin coconut shell, with a CTC rate of 60. Anyone matching a refill by eye will find a standard cartridge sits loose in a 4+ frame and lets air past the edges. The half inch of extra depth is not cosmetic, and it is the reason the two parts carry different codes in the first place. Check the model on the housing plate before matching a cartridge to it.
Planning Around an Airbox 4 Plus Replacement Filter
An airbox 4 plus replacement filter set is a real line item, so it belongs in a maintenance budget rather than an emergency one. This is commercial equipment moving a lot of air. Carbon loads in proportion to the volume passing through it, not to the days on a calendar. A room running near the top of the range will go through media faster than a room using the unit at its recommended airflow. Keep the pre-filter changed on schedule, because it is the part that stops dust reaching the carbon and it costs a fraction as much. Swap all four cartridges at once, seat them flat against the frame, and check the gaskets before closing the door. Air finds any gap in a seal and goes around the media rather than through it. That is the failure nobody notices until the room starts smelling again. Log the fitting date somewhere you will find it next year.
Key Features
- XL cartridge, 16 x 24 x 1.5 in: Thicker than the standard Air Box cartridge, and not interchangeable with it.
- Four per housing: A complete refill for the 4+ means four of these, changed together.
- Built for 3500 CFM: The extra depth holds contact time at the airflow this housing passes.
- 100% activated charcoal: Premium virgin coconut media with a stated CTC rate of 60.
- Pre-filter does the heavy lifting: Keeping it changed is what stretches the life of the carbon behind it.
Technical Specifications
| Specification | Value |
|---|---|
| Brand | Air Box |
| Product | Refill Carbon Cartridge, XL |
| Part Number | HT4504 |
| Fits | Air Box 4+ only |
| Quantity | Single cartridge |
| Cartridge Size | 16 x 24 x 1.5 in |
| Cartridges Per Housing | 4 |
| Housing Rating | 3500 CFM, 12 in flanges |
| Media | 100% activated charcoal, premium virgin coconut |
| CTC Rate | 60 |
| Typical Service Life | 18 to 24 months |
| Returns | 14 days from delivery if unused, with a 30% restocking fee and return shipping paid by the customer, per the Air Box manufacturer policy |