--- title: "Undercounter ice maker: gravity drain or drain pump?" description: "Why an undercounter unit sends water away every day, when a steady slope to a lower drain is enough, when only a pump will do, and the questions to settle…" url: "https://icemakerrepair.center/guides/undercounter-ice-maker-gravity-drain-or-pump/" date_modified: "2026-09-26" --- Choosing and comparing # Undercounter ice maker: gravity drain or drain pump? Choose an undercounter ice maker drain pump when the nearest drain sits higher than the unit's outlet, lies far away, or is reached through a sink tailpiece or standpipe. A gravity drain works only when the line can fall steadily, about a quarter inch per foot, to a lower drain with no loops or traps. Gravity has fewer parts; a pump fits almost anywhere. By [IceMakerRepair.center technical team](https://icemakerrepair.center/authors/technical-team/) Published September 26, 2026 ## At a glance. Unlike the ice maker in a freezer, an undercounter unit sends water away every day, and that water needs a route chosen before the unit arrives. Gravity drain or pump is really a question about where the nearest drain sits and how far below the unit it is. Read the whole guide ### Why it drains at all Rinse water from each freeze and meltwater from an insulated bin A clear-ice unit sends away the water it refuses to freeze. ### What gravity needs A drain lower than the outlet and a steady fall Makers give about 1/4 inch of drop per foot of run. ### What a pump adds Lift to a sink tailpiece, disposal or standpipe U-Line rates its P60 for 10 feet of lift; Sub-Zero lists 12 feet of rise on its pump models. ### When to decide Before the unit is ordered Many models are sold as separate gravity and pump versions. In this guide 1. Why an undercounter unit needs a drain at all 2. When a gravity drain is enough 3. When a drain pump is the only answer 4. Living with each choice 5. Questions to settle before the unit is ordered 6. Questions ## Why an undercounter unit needs a drain at all A clear-ice unit freezes only part of the water it circulates. The rest, carrying the minerals and air it rejected, is flushed out at the end of each cycle. The storage bin adds a second stream: Sub-Zero points out that its undercounter bins are insulated rather than refrigerated, so the cubes melt slowly and that meltwater runs away all day long. Without a working drain, all of that water has nowhere to go but the bin and then the floor. That is why the drain on these units is not an accessory to add later. It is as much a part of the installation as the supply line that feeds the unit, and it deserves the same planning. Source: [Sub-Zero — Sub-Zero ice types](https://www.subzero-wolf.com/assistance/answers/sub-zero/common/sub-zero-ice-types) — Undercounter bins are insulated but not refrigerated, so the ice melts continuously ## When a gravity drain is enough Gravity is the simplest arrangement and the one with nothing to wear out. It needs a drain point below the unit's drain outlet and a line that runs downhill the whole way. U-Line and Sub-Zero both give the slope as a quarter inch of fall for each foot of horizontal run, and Scotsman adds that the hose must have no dips, loops or kinks along the way. - A floor drain or basement drain line lower than the unit's outlet. - A run that keeps falling from end to end, with no stretch that climbs. - A path that stays above freezing, with insulation wherever the line could sweat. ### How low the outlet sits The drain connection on an undercounter unit sits close to the floor; Sub-Zero places the one on its UC-15I at roughly five inches up. A kitchen sink drain is well above that, so a unit tucked beside the sink normally cannot empty into it by gravity. A floor drain, a basement below with a drain line to reach, or a crawlspace where the hose can drop are the usual gravity routes. ### Why the drain cannot sit directly underneath U-Line warns that its units have a solid base and cannot drain into the floor straight below themselves, so the line must leave the cabinet and turn. The same guide asks for a line without traps that is vented as local code requires, because a trap with no vent lets water back up into the bin. Source: [Sub-Zero — UC-15I gravity drain or pump selection considerations](https://www.subzero-wolf.com/assistance/answers/sub-zero/undercounter-ice-makers/uc-15i-gravity-drain-or-pump-selection-considerations) — Drain connection about 5 inches from the floor; 1/4 inch fall per 12 inches; pump models rise up to 12 feet and run up to 100 feet and likely need an air gap; the gravity model drains with the power off; [U-Line — Clear ice maker user guide and service manual (U-CLR1215B)](https://www.u-line.com/userguide/pdf/index/sku/U-CLR1215B-00B/) — Gravity drains fall 1/4 inch per foot with no traps and venting per local code; the unit cannot drain directly below itself; -40/-47 models have a factory pump; the P60 pump lifts up to 10 feet; [Scotsman Home Ice — Choosing the right drain for undercounter units](https://scotsmanhomeice.com/designing-for-ice-choosing-the-right-drain-for-undercounter-ice-machines/) — Gravity drains need a lower drain point and a slope of at least a quarter inch per foot with no dips, loops or kinks; a pump model works in either application Close on a small drain pump and its tubing inside the base of an undercounter ice maker, the panel off. ## When a drain pump is the only answer Most kitchens and islands have no drain below an undercounter unit's outlet. An undercounter ice maker drain pump solves that: it collects the drain water in a small reservoir, then pushes it up and across to a sink tailpiece, a disposal inlet or a standpipe. Scotsman notes that a pump model works in either situation, which makes it the safer order when the route is uncertain. Limits apply. U-Line rates its P60 pump for a lift of up to 10 feet, placed as close to the rear of the unit as possible, and Sub-Zero lists a maximum rise of 12 feet and a run of 100 feet for its pump models. Sub-Zero also says pump installations will likely need an air gap device so drain water cannot flow back into the unit, with local plumbing code setting the details. ### Ordering the right version Many undercounter models are sold in separate gravity and pump versions, and the model number tells them apart. U-Line, for instance, marks its factory pump units with a -40 or -47 suffix and its gravity units with -00 or -07. Check that suffix before the unit ships, since adding a pump afterward means a separate part and a service visit. Source: [Sub-Zero — UC-15I gravity drain or pump selection considerations](https://www.subzero-wolf.com/assistance/answers/sub-zero/undercounter-ice-makers/uc-15i-gravity-drain-or-pump-selection-considerations) — Drain connection about 5 inches from the floor; 1/4 inch fall per 12 inches; pump models rise up to 12 feet and run up to 100 feet and likely need an air gap; the gravity model drains with the power off; [U-Line — Clear ice maker user guide and service manual (U-CLR1215B)](https://www.u-line.com/userguide/pdf/index/sku/U-CLR1215B-00B/) — Gravity drains fall 1/4 inch per foot with no traps and venting per local code; the unit cannot drain directly below itself; -40/-47 models have a factory pump; the P60 pump lifts up to 10 feet; [Scotsman Home Ice — Choosing the right drain for undercounter units](https://scotsmanhomeice.com/designing-for-ice-choosing-the-right-drain-for-undercounter-ice-machines/) — Gravity drains need a lower drain point and a slope of at least a quarter inch per foot with no dips, loops or kinks; a pump model works in either application ## Living with each choice A gravity drain is silent and has no part to replace, and Sub-Zero notes that its gravity model keeps draining on its own with the power off. Its weak point is the route: a hose that sags, a trap that forms as a cabinet settles or a floor drain that slows will back water into the bin. A pump brings a motor, a sensor that starts it and a check valve, so it adds a short hum under the counter and one more thing that can wear. When a pump stops, the bin fills and overflows, usually onto the floor in front of the unit. Slime and scale in the pump reservoir are frequent reasons, which is one more argument for keeping to the cleaning schedule. - Gravity: fewest parts and no noise, but entirely dependent on slope and a lower drain. - Pump: fits islands, slab floors and upper stories, and adds a motor to look after. - Either one: a clogging line shows up as water standing in the bin before it reaches the floor. Source: [Sub-Zero — UC-15I gravity drain or pump selection considerations](https://www.subzero-wolf.com/assistance/answers/sub-zero/undercounter-ice-makers/uc-15i-gravity-drain-or-pump-selection-considerations) — Drain connection about 5 inches from the floor; 1/4 inch fall per 12 inches; pump models rise up to 12 feet and run up to 100 feet and likely need an air gap; the gravity model drains with the power off ## Questions to settle before the unit is ordered Answer these with a tape measure and a flashlight in the cabinet you plan to use. They decide which version to buy, and they spare the kitchen a trench through the floor or a pump retrofit a year later. 1. Where is the nearest drain, and is it lower than the unit's drain outlet? 2. Can the line run downhill the whole way without climbing over a toe kick or a cabinet rail? 3. If a pump is needed, is a sink tailpiece, disposal or standpipe within its rated lift and run? 4. Does local code call for an air gap, and is there room for one? 5. Is there a dedicated outlet placed where a leaking line will not reach it? ## Where to stop Turn the unit's water supply valve off before anyone disconnects a drain hose, and pull the plug before a pump housing is opened. If an undercounter unit has already overflowed, keep clear of standing water around any outlet inside the cabinet and switch the breaker off only while you are standing somewhere dry at a dry panel. New drain routes through a floor, a wall or a concrete slab are a plumber's job. Written by [IceMakerRepair.center technical team](https://icemakerrepair.center/authors/technical-team/). The technicians sent out when an ice maker visit is booked on this site. They write from what they find at the supply valve, along the fill tube, in the ice bin and at the drain, and they check it against the maker's own manuals wherever one is published. Sources: [Sub-Zero — Sub-Zero ice types](https://www.subzero-wolf.com/assistance/answers/sub-zero/common/sub-zero-ice-types) · [Sub-Zero — UC-15I gravity drain or pump selection considerations](https://www.subzero-wolf.com/assistance/answers/sub-zero/undercounter-ice-makers/uc-15i-gravity-drain-or-pump-selection-considerations) · [U-Line — Clear ice maker user guide and service manual (U-CLR1215B)](https://www.u-line.com/userguide/pdf/index/sku/U-CLR1215B-00B/) · [Scotsman Home Ice — Choosing the right drain for undercounter units](https://scotsmanhomeice.com/designing-for-ice-choosing-the-right-drain-for-undercounter-ice-machines/) For the heart of your home. ## Questions owners ask. ### Can an undercounter unit empty into the sink tailpiece by gravity? Rarely. The drain outlet on these units sits a few inches above the floor, below the level of a sink tailpiece, so the water would have to run uphill. That connection almost always calls for a pump. ### Why is water standing in the bottom of my bin? A slow drain is the usual reason: a sag or trap in a gravity line, a kinked hose behind the unit, or a pump that no longer starts. Turn the water supply off and have it looked at before the bin spills over. ### Does a drain pump make the unit noticeably louder? A little. The pump runs in short spells as its reservoir fills, and most owners hear it as a brief hum under the counter rather than a constant sound. ### Can a gravity model be converted to a pump later? On many models a pump kit exists; U-Line's user guide covers fitting its P60 into a unit that shipped without one. It is a service job that means opening the unit and rerouting its drain tubing. ## The problems behind it. Each has a page of its own: what it usually means and the causes in the order worth checking. [All 17 problems](https://icemakerrepair.center/problems/) Problem ### Undercounter Ice Maker Not Draining 5 causes, cheapest first Water on the floor or near power ### Undercounter Ice Maker Overflowing 6 causes, cheapest first Water on the floor or near power ### Ice Maker Leaking on the Floor 6 causes, cheapest first Problem ### Ice Maker Making Noise 6 causes, cheapest first ## When it needs a technician. The repairs on the right are where this guide ends when the checks do not settle it. ### Drain pump and drain line repair The drain that carries meltwater and unused water out of a built-in ice maker, whether by gravity or with a small pump, cleared, re-routed or given a new pump when water stands in the bin or spills out of the door. ### Undercounter ice maker cleaning and descaling A full cleaning and descaling of a built-in or countertop ice maker: scale off the plate, cylinder or fingers, slime out of the reservoir and drain, the condenser brushed, and the unit sanitized before the ice comes back. ### Diagnostic visit A visit that traces the water from the supply valve to the bin and back out through the drain, and names the one part that stopped the ice before anything is ordered. ## More in choosing and comparing. Nugget, clear or crescent ice, whether a failing ice maker deserves a repair or a new assembly, and what a gravity drain or a drain pump means before an undercounter unit goes in. [The whole section](https://icemakerrepair.center/guides/choosing-and-comparing/) Deciding what ice maker to keep or buy ### Nugget, clear or crescent ice: what each kind of ice maker gives you How a molded tray, a chilled plate and an auger each freeze water, how the ice behaves in a drink, and what each design asks of the house in plumbing and upkeep. Deciding what ice maker to keep or buy ### Repair the ice maker or replace the whole assembly? When a new module is the right repair, when the trouble is really the valve, the filter or a frozen fill tube, and why undercounter and countertop units follow different rules. Guides ### All 18 guides Six sections, by what you are trying to find out. --- **[Read on the site: Undercounter ice maker: gravity drain or drain pump?](https://icemakerrepair.center/guides/undercounter-ice-maker-gravity-drain-or-pump/)** **[Book a visit with IceMakerRepair.center](https://icemakerrepair.center/schedule/)**