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Sun Frost Energy Efficient Shower – Version 4.0

by Larry Schlussler PhD on April 1st, 2014

I recently finished the latest of our “Energy Efficient Shower” See link for theory of operation: IMG_1279_1436 The enclosed design of the shower worked well in the installed space, it eliminated the need for adding an exhaust system to the room, or the need to heat the space. The room it’s located in is seldom above 60 deg F.


The shower is made of what may be called “SIPS” panels. The panels were made out of 1” extruded polystyrene sandwiched between two sheets of 1/8” plywood. The inside surfaces were covered with high pressure laminate. The base of the shower is a 32” square standard shower pan. The bottom of the walls are covered with aluminum angle to assure that no moisture penetrates into the edge grain of the plywood or laminate.

IMG_1282_1439The doorway is framed by a wood structure. The curtain hangs below a 3/8” piece of clear “Plexiglas” Two magnets lie behind the fiberglass base. The bottom corners of the curtain are held taught by another set of magnets. Two layers of curtain material give a bit of extra insulation.

The ceiling of the shower is covered with heavy duty “Reflectix”. About 1/3 of the ceiling opens to ventilate when finished showering.


The shower is extremely comfortable to use, it is located several feet from a hot water heater so hot water is provided almost instantly. In a 60 deg F room what feels like a very warm shower can be taken with 98 deg F water. Entrance water to typical showers is about 110 deg F. Water flow rate of one gallon/minute feels generous. If desired the flow could be reduced to ½ gallon/minute without reducing thermal comfort.

IMG_1284_1441The temperature drop from the shower head to the floor was only about 1 deg F. Temperatures drops measured in a typical shower are about 22 deg F. Knowing the flow rate and temperature drop the amount of moisture evaporated into the bathroom air can be calculated.

With a 2 gallon per minute (16 pounds/minute) shower and a 22 deg F drop in water temperature the evaporated per minute cooling rate is about 550 Btu/minute. At this rate about 8 oz. of water will be evaporated per minute or for an 8 minute shower ½ gallons of moisture will be added to the air. To remove this moisture typically requires energy for ventilation and reheating of cold air to make up air during the winter. This feature is particularly valuable when mold growth is a problem and in homes which are well sealed for energy conservation.

IMG_1289_1443This simple redesign of the conventional shower saves energy, water, minimizes moisture problems and it also simplifies a homes ventilation system.

For more variations on this design see the ASES paper describing the shower in my home:

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