Condensation inside a glass door: seal, heater or habit

Which side of the glass is wet

Do this before anything else and do it with a dry cloth on both faces. Moisture on the room side means the outer pane is colder than the dew point of the air in the room, which is a question about the room and about the heater circuit that exists to prevent exactly this. Moisture on the cabinet side means humid air is arriving inside the cabinet faster than the cold surfaces can be kept dry, which is a question about the gasket, the door closure and how the cabinet is being used. Moisture you cannot reach from either side is inside the glass assembly itself, and no amount of adjustment or cleaning will touch it. Those three findings send you down three different roads, and the reason to spend two minutes here is that people routinely replace gaskets on a cabinet whose glass had failed, and vice versa.

• Room side, wipes clear: the dew point in the room is above the temperature of the glass
• Cabinet side, wipes clear: humid air is entering, or the cabinet is being asked to hold too much of it
• Between the panes, will not wipe: the sealed glass unit has lost its perimeter seal
• Droplets on the interior back wall and shelves rather than the glass: usually normal in humid weather

The dew point arithmetic that explains most of it

Condensation is not a fault, it is a temperature. Any surface colder than the dew point of the air touching it collects water, and that is true of a glass door, a cold drink and a window. Put numbers on it and the complaint usually explains itself. A room at 75F holding 60 percent relative humidity has a dew point near 60F. A wine cabinet holding its contents at 55F therefore has a door that is below the dew point of the room it is standing in, and it will sweat, and nothing in the appliance is broken. Drop that same room to 40 percent humidity and the dew point falls to about 50F, the glass sits above it, and the sweating stops without anyone touching the cabinet. That is why this is a seasonal complaint, why a cabinet that was dry all spring starts in the humid stretch of late summer, and why a unit in an unconditioned bar area or a pantry behaves nothing like the identical unit in the kitchen it opens off.

• A room at 75F and 60 percent humidity has a dew point near 60F, so a 55F door will sweat
• The same room at 40 percent humidity has a dew point near 50F, and the glass stays dry
• Setting a long-term storage zone colder than the wine needs buys sweating and nothing else
• Unconditioned bar areas, pantries and butler's kitchens run hotter and wetter than the room beside them
• Cold glass, warm humid air: the water has to go somewhere, and the glass is the coldest thing in reach

Anti-sweat heaters, the part that exists for this exact problem

Glass-door refrigeration carries a low-wattage heater around the door perimeter, in the frame, or in the mullion between two doors, and its entire job is to hold those surfaces above the dew point of the room. It draws very little, it makes no noise, and nobody knows it is there until it stops. The failure has a signature worth learning, because it separates a heater circuit from a gasket without any tools at all. A heater fault produces a band of moisture at the frame and around the edges of the glass rather than a general fog across the middle of the pane, the frame feels cold to the touch where it used to feel close to room temperature, and it tracks the weather rather than the door: bad on humid days, absent on dry ones, and unrelated to how often anyone opens it. Before condemning the circuit, confirm the unit is not sitting in an energy-saving mode, because some equipment reduces heater output in that setting and the symptom is identical.

• A band of moisture at the frame and glass edges rather than fog across the middle of the pane
• A frame that feels cold where it used to feel about room temperature
• Worse on humid days, gone on dry ones, and unaffected by how much the door is used
• Confirm the unit is not in an energy-saving mode that reduces heater output before quoting a part
• The heater is inside the door or frame assembly, so this is a technician's job rather than a shelf part

When the seal or the door is what is letting the air in

Moisture on the cabinet side is air getting in, and on a glass door the weight of the door is usually what lets it in. A strip of paper closed in the seal should drag when you pull it, and the place to start is the bottom hinge corner, because that is where the mass of a glass door is carried and where it drops first. Then look past the seal at the mechanics, because a good share of these are not the gasket at all. Is the door actually closing, or is a shelf rail sitting proud, a bin over-filled, or a bottle neck holding it a fraction open. Is the cabinet still level, since a unit that has settled or a floor that has moved lets a heavy door hang away from its seal. Is the gasket hard, torn at a corner, or simply dirty, because grime or mold worked into the folds stops an otherwise sound seal from sealing. Warm water and mild soap, dried properly afterward, is the whole of what should ever go near it. No solvents and no petroleum products.

• Bottom hinge corner first, because that is where the weight of a glass door is carried
• A shelf rail, an over-filled bin or a bottle standing proud will hold a door slightly open
• A cabinet that has settled out of level lets a heavy door hang away from its seal
• Grime or mold in the folds stops a sound gasket from sealing: warm water, mild soap, then dry it
• Hinge and closer adjustment on a heavy paneled or glass door is technician work, not a screwdriver job

Fogging between the panes, and what that one costs

A glass door on this equipment is an insulated glass assembly: two or three panes with a spacer between them and a sealed cavity, often with a low-emissivity coating and sometimes a gas fill, and that assembly does most of the work of keeping the outer pane above the dew point in the first place. When the perimeter seal fails, room air and the moisture in it get into the cavity and condense there. It will not wipe off from either side. It tends to clear in dry weather and return in humid weather, which is exactly why owners live with it for a year before calling anyone. After it has been happening a while there is usually a permanent haze or a mineral outline left on the inner surfaces that stays visible even on a dry day. There is no repair at the pane. The glass assembly is replaced, and on most units that means the door, which makes this the one condensation fault here that is a serious number rather than a service call. It is also worth knowing that a failed assembly has lost its insulating value, so the cabinet is working harder than it should be as well as looking wrong.

Habit, and the things you can change this afternoon

Every door opening trades a cabinet full of cold settled air for a cabinet full of warm room air, and a wine cabinet in an entertaining space that gets opened twenty times in an evening will complain about it for hours afterward. Warm bottles or warm food loaded in bulk do the same thing more slowly. So does a door propped open on its stop while somebody decides, a humidifier running in the same room, a dishwasher venting steam a few feet away, a range used hard without effective ventilation, or windows left open through a humid evening. Wiping the glass with a wet cloth and not drying it accounts for more panicked phone calls than it should. Set against that, know what is not a fault. A refrigerator compartment is supposed to be humid, and on dual-refrigeration equipment that humidity is deliberately kept in the fresh food section instead of being allowed anywhere near the freezer, so a little moisture on the back wall or the shelves in August is the system doing its job. A wine cabinet is meant to be humid too. There is a real difference between correct humidity and water running down the inside of the glass.