AprilAire 4788 Humidifier Maintenance Kit with No. 45 Water Panel

AprilAire 4788 is a whole-house humidifier maintenance kit for AprilAire models 400, 400A, and 400M. It combines a No. 45 water panel with replacement maintenance components, so it is intended for a broader service refresh than a filter-only replacement.

At a glance

The listing identifies compatibility with AprilAire whole-house humidifier models 400, 400A, and 400M.
The claimed kit components include a No. 45 water panel and several water-distribution and float-related parts.
The listing recommends replacing the water panel twice during the season.

Price

$116.99Save 15%

Reference price: ~~$137.99~~

Price checked: Nov 12, 2026

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Often bought together

AprilAire 45 Water Panel Humidifier Filter Replacement for AprilAire Whole-House Humidifier Models 400, 400A, 400M (Pack of 2)

$29.60

Aprilaire Genuine OEM Water Level Sensor Assembly 4410 for Model: 400

$49.87

Pros and cons

Pros

Includes components beyond the water panel, which may suit scheduled maintenance when several listed parts are due for replacement.
The listed compatible models make it easier to distinguish this kit from AprilAire kits intended for other humidifier models.

Technical specifications

6 specifications

Identity
Brand listed	Research Products Corporation
Model	4788

Compatibility and dimensions
Listed humidifier models	400, 400A, 400M
Water panel dimensions	12.875" H x 9.875" L x 1.75" W
Product dimensions listed	1.75 x 9.88 x 12.88 inches
Weight listed	0.01 ounces

What to know before buying

The listing recommends replacing the water panel twice during the season. Consult the humidifier owner's manual before maintenance. The stated 40%–60% humidity range and associated health benefits are manufacturer claims, not independently verified outcomes.

What’s in the box

Water Panel (45)Check selected pack
Scale Control Insert (4403)Check selected pack
Water Distribution Tray (4407)Check selected pack
Feed Tube with Compression Sleeve and Nut (4335)Check selected pack
Yellow Orifice (4231)Check selected pack
In-line Strainer (4004)Check selected pack
Float Assemblies (4406)Check selected pack
Float Cover (4405)Check selected pack
Owner's ManualCheck selected pack

Check which accessories are included in your selected pack before buying.

Who is it for?

A good fit for

Owners maintaining an AprilAire 400, 400A, or 400M whole-house humidifier who want the listed water panel and service parts together.

Less suited to

Owners of other humidifier models unless their model's documentation confirms compatibility.
Buyers who need only a replacement water panel and do not need the other listed maintenance components.

AprilAire 4788 Humidifier Maintenance Kit with No. 45 Water Panel · photo 2 — Additional product photo 2

Customer reviews on Amazon

4.7 / 5 · 110 ratings

5 stars82%82%
4 stars12%12%
3 stars4%4%
2 stars1%1%
1 star1%1%

Customer feedback highlights OEM quality and fit. The listing also identifies specific compatible models, so those fit reports are most relevant when the buyer's humidifier is a 400, 400A, or 400M. Aggregate ratings are largely five-star, but ratings alone do not establish fit for every installation.

Positive themes

Customers describe the kit as an OEM product that fits well.

Frequently asked questions

Which humidifier models is the AprilAire 4788 listed for?

The listing names AprilAire whole-house humidifier models 400, 400A, and 400M.

What parts does the kit listing name?

It names a Water Panel (45), Scale Control Insert (4403), Water Distribution Tray (4407), Feed Tube with Compression Sleeve and Nut (4335), Yellow Orifice (4231), In-line Strainer (4004), Float Assemblies (4406), Float Cover (4405), and Owner's Manual.

How often does the listing recommend replacing the water panel?

It recommends replacing the water panel twice during the season. Follow the humidifier owner's manual for maintenance instructions.