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What filter does a AprilAire 4000 take?
It takes the AprilAire Water Panel #45 — OEM part number 45.
AprilAire 4000, whole-house humidifier, whole house.
Lowest verified price: $17.90 — 1 panel, genuine AprilAire 45 at eBay (Buy It Now listing). eBay listing shipping terms (marketplace; verify before relying). Checked 2026-11-11.
Buy the 45 on Amazon — 45Amazon search for the exact part number (no single listing is endorsed). Amazon price is shown on Amazon; we do not quote it here.
The part, in brief
| Part | AprilAire Water Panel #45 |
|---|---|
| Replacement interval | Replace every year or every 6 months (AprilAire guidance). |
| Per change | Genuine retail 45RP is a 2-pack; watch pack counts when comparing prices. |
| Equivalents | BestAir A45, Honeywell HC22E1003, Orzechowski H1071 |
Verified prices
| Option | Price | Store & shipping |
|---|---|---|
| Genuine (OEM) 1 panel, genuine AprilAire 45 | $17.90 | eBay (Buy It Now listing) eBay listing shipping terms (marketplace; verify before relying) · Checked 2026-11-11 · source |
| Genuine (OEM) 1 panel, genuine AprilAire 45 | $26.99 | DiscountFilters Free shipping on orders $70+ at DiscountFilters; a fee applies below that · Checked 2026-11-11 · source |
Genuine prices only: the eBay figure is a marketplace Buy It Now listing, and no established-retailer aftermarket price was captured this pass.
Full record with every price, source and date: AprilAire Water Panel #45 page.
Finding the model number on a AprilAire
Whole-house (furnace-mounted) models: the model number is on the humidifier cover or the side of the cabinet mounted on your ductwork. The water panel number (10 or 35) is printed on the old panel's frame.