Afternoon Sun on a West-Shore Kitchen and the Wine Unit in It

Sunlight does two separate things to a wine cooler, and the glass deals with only one of them. Along Mercer Island’s west shore the afternoon sun comes in low across the lake, through windows placed for the view, and in some kitchens it lands squarely on a glass wine door.

Light and heat are different problems

Sub-Zero names heat, humidity, vibration and light as the four enemies of wine, and afternoon sun brings two of them at once. The light matters because of the ultraviolet part you cannot see, which passes through clear glass and works on wine over time. That is why cellars are dark. The heat is simpler. Sun falling on the door and the cabinet face warms them, and the unit then has to pump that warmth back out.

What the glass does, and what it does not

Sub-Zero describes the glass on its wine storage as UV-resistant and bronze-tinted, there to shield the wine from that invisible light. For a unit standing in a bright room, that is a real protection. More about the door as a part, including damage and cleaning, is on the glass door page.

The coating and the tint are about light, though, not temperature. A door that has had the sun on it for an hour is warmer than one in shade, whatever glass is in it. Sub-Zero’s own troubleshooting notes that warmer surroundings make the compressor run longer, and a sunlit unit does exactly that through the afternoon. The zone the light falls on warms first, and on a unit with two zones that is usually the one nearer the window.

Heat reaching a unit from the side, from a range or a wall oven next to a wine column, is a related but separate case, and the Holding the Zones note on heat next door takes it up.

Simple changes that help

Shade the window, not the unit. A blind or shade drawn through the hours the sun reaches the door keeps the direct light off it, and it costs the view for only part of the day. Never hang anything over the kickplate grille at floor level, where the unit sheds its heat.

Put the bottles you are keeping longest where the light does not reach, and use the sunny front positions for what you will open soon.

Mind the interior lighting. On its undercounter units Sub-Zero switches the lights off when a door has been left ajar, to keep their heat out of the cabinet, and on the current Designer undercounter models with glass doors the accent lighting can be set lower or turned off. In a room that already takes the afternoon sun, there is no reason to add light inside the cabinet as well.

When the sun has become a fault

A zone that rises in the afternoon and settles again by morning is a unit coping with its surroundings. The picture changes when the zone no longer recovers overnight, when the unit runs almost without pause after dark, or when both zones are warm on a cloudy day. By then the sun is only exposing something else, usually a condenser behind the kickplate that can no longer shed heat, a zone’s fan that has slowed, or a sensor that reads wrong.

Those are the things we check on a wine storage repair visit, and your two readings, one late in the afternoon and one the next morning, tell us where to start.

Before you call

1. Step 1

   Note when the sun reaches the unit

   Which months, which hours, and which part of the door it falls on. A week of rough notes on a phone is plenty.

2. Step 2

   Probe the sunlit zone twice

   Put a probe thermometer into a tumbler of water and set it among the bottles in that zone. Read it late in the afternoon, then again first thing the next morning.

3. Step 3

   Draw the blind for a few days

   Shade the window through the sunny hours and take the same two readings. If the afternoon rise shrinks, the sun was doing it.

4. Step 4

   Move the long-keeping bottles back

   Put the bottles you intend to keep for years at the back, or in the zone the light does not reach, and the ones you will open soon at the front.

Past these checks the fault is inside the machine. Call Mercer Island Sub-Zero Service on (206) 208-3377 and say which step changed nothing.

Asked about this

Does UV-resistant glass make it safe to keep a wine unit in the sun?

It deals with the part of sunlight Sub-Zero singles out as a risk to wine, the invisible ultraviolet that can reach through a bottle. It does nothing about warmth. Sun on the door and the cabinet face still heats them, the compressor runs longer to make up for it, and the zone the light falls on warms first. Shading the window helps both.

The zone nearest the window warms every afternoon and recovers overnight. Is that a fault?

Probably not, as long as it recovers fully and the unit is not running without a break. That is the unit catching up once the sun moves off. If the zone stops recovering by morning, or the afternoon rise keeps growing, Mercer Island Sub-Zero Service, (206) 208-3377, would check the condenser, the fan for that zone and its sensor.