Honeywell HUL588 Top Fill Plus Ultrasonic Humidifier review

Honeywell’s HUL588 Top Fill Plus is the electronic-control companion to the simpler HUL585: both are 1.25-gallon ultrasonic cool-mist humidifiers with the same top-fill handling and separate aroma pad, but the HUL588 adds a humidistat that can cycle the mist around one of five approximate humidity levels. That matters if you want the machine—not a person watching a dial—to respond as the room changes. It is still a physical-button appliance, not a phone-connected or display-led model.

What changes from the HUL585

The shared owner’s manual is explicit about separating the two controls: the HUL585 has a power knob, while the HUL588 has electronic controls. On the HUL588, pressing the humidity control cycles through approximate settings of 30%, 40%, 50%, 60% and 70% relative humidity. Once selected, the humidifier turns mist off and back on as the reading reaches or falls below that level. A green reached-status icon lets you know when the mist has paused. You can also run continuously by cycling until no humidity level is selected. This is a set of discrete appliance-side choices, not a numeric room readout or an app slider, and the manual cautions that the displayed percentages are approximate.

Three mist-output levels—low, medium and high—are selected separately. High output can deliver more moisture but draws down the tank sooner; the manual does not promise a runtime or square-foot coverage figure for this model. A timer, remote, Wi-Fi/app control and warm-mist setting are not documented. If you want a numeric display and an appliance timer, Honeywell’s HEV620 is an evaporative tower with a different wicking-filter and room-airflow routine. The HUL588 keeps the visible ultrasonic mist and filter-free design of the HUL585 while adding automatic cycling.

Refilling, mist and placement

The manual gives a combined tank-and-reservoir capacity of 1.25 gallons (4.7 liters) for the HUL585/HUL588 series. You can remove the tank by its handle and fill it at a sink, or leave it seated and pour cool water through the wide top opening with a pitcher. The volume is useful for reducing how often you refill, but a full tank is still a substantial carry; consider the sink route if you would rather not lift and transport it. This model makes a visible cool mist through an ultrasonic nebulizer, so put it on a firm, level, water-resistant surface and direct the adjustable two-way outlet away from walls, bedding, furniture and electronics. Honeywell’s manual calls for at least 12 inches of clearance from walls and four feet from a bedside.

Ultrasonic output can carry minerals from hard tap water into the room as white residue. Honeywell discusses distilled water or its optional HDC500 demineralization cartridge as ways to reduce mineral deposits; the cartridge’s present availability was not established in this review. The reached light and auto-cycling do not substitute for checking room conditions: if condensation forms around the unit or on windows and walls, the manual says humidity is too high and the humidifier should be turned off or the room aired until it drops. A comfortable range stated in the instructions is 40–60%, so the 70% setting is not a reason to ignore condensation or the room itself.

Cleaning and the separate aroma pad

The HUL588 has no replaceable wick, but filter-free does not mean low-maintenance. Honeywell recommends fresh water daily and weekly cleaning. The shared manual has separate scale-removal and disinfecting steps, thorough rinsing between them, and specific instructions for the float paddle and fragile nebulizer. Do not submerge the base or improvise cleaning around the electrical parts; follow the manual’s exact sequence. The manual does not identify dishwasher-safe components. In a hard-water home, expect to pay closer attention to mineral scale and clean the nebulizer as needed rather than waiting for output to fade.

An included separate oil pad and tray allow passive evaporation of a small amount of fragrance without putting it in the water. It is not a water-contact diffuser. The manual forbids essential oils, medication and inhalant liquids in the tank, base, reservoir or mist outlet. If you need a true diffuser, choose a separate device; the pad is an optional side feature, not a reason to alter the humidifier’s water path.

Who should shortlist it?

The HUL588 suits someone who wants top-fill ultrasonic cool mist, a filter-free plan and a humidity setting that can make the unit stop and restart automatically. In the finder, selecting top-fill, ultrasonic operation, buttons with indicator lights, sensor-based humidity response and a selected humidity target describes this configuration. Choosing an appliance timer, numeric display, app control, or warm mist should remove it. The control panel uses status icons rather than a numeric humidity display, and its five target levels are approximate.

Choose the HUL585 instead if you prefer the manual rotary knob and are comfortable monitoring room humidity separately; it has the same series capacity and refill choices but does not document automatic humidity setpoint cycling. Choose an evaporative alternative such as the HEV620 if an on-device humidity display and timer are more important than visible mist and filter-free upkeep. None of these options erases the practical cleaning and water-quality tradeoffs: compare the exact care routine you can sustain, not only the control panel.

Exact identity and evidence limits

Honeywell’s current support directories call this model Top Fill Plus, HUL588. The official device registry lists black HUL588B and white HUL588W model versions as in commercial distribution; both are finish variants of the same manual-defined control plan, not different humidification modes. The exact HUL588B manufacturer-image link was observed, but the host returned a Cloudflare 403 when its bytes were requested, so no product image is presented as verified in this draft. The image gap does not change the model facts, but it remains a release task. No hands-on runtime, noise, room-coverage or durability test is claimed; the shared manual and exact-model registry/support evidence are the basis for this assessment.