Ice Box Design

Building or modifying an insulated ice box.

Efficient performance from a refrigeration system depends primarily on a good design for the box with sufficient insulation and an air tight construction.

Many boat builders today are constructing excellent boxes but there are many situations where improvements or modification of the box will dramatically improve the performance. Adding insulation to the bottom or sides of a box will often help improve the insulation value, reduce the volume and improve the shape of an existing box.

Building a new box from scratch is a big project but it can be done with very good results.

Here are a few general suggestions.

How much is enough? Is more always better? The answer to these questions like so many questions is "it depends". Insulation works on a diminishing return. The first inch gives the most benefit and each additional inch provides less benefit.

Heat gets into the cabinet not only through the insulation but also through opening the door or putting warm things into the refrigerator, less than perfect seals, the door frame, etc. The shape of the box is a huge factor since it is the surface area not simply the volume that is important.

In general, the rule of thumb goes like this:

For a refrigerator box:
4 cu ft or less, use a minimum of 2 inches.
6 cu ft will need 3 inches
bigger than 8 cu ft needs 4 inches

For a freezer:
2 cu ft or less, 4 inches minimum.
4 cu ft or less, 5 inches.
larger than 4 cu ft, 6 inches.

To summarize
Keep the box small and an efficient shape (square is the ideal).
A front loading box is not a problem as long as the door seals are tight.
If you have a separate freezer be sure to have it well insulated and no larger than necessary - empty space in a freezer will still use power.

What kind of insulation? We recommend extruded polystyrene - such as Dow Blueboard or Owens Insulpink. It is conservatively rated at R-5 per inch and will not absorb moisture so it will maintain its insulation value. Other foams may have higher initial insulation values but may quickly degrade in the wet marine environment. Vacuum panels can achieve much higher insulation values but they are very expensive, fragile and difficult to handle.

Extruded Polystyrene insulation is usually available in sheets of several thicknesses up to 2". It is easy to work with and it can be cut on a table saw. It is easy to obtain at a local builders supply and is not expensive.

A new interior liner can be made with Strutoglas flexible fiberglass panels - made by Kemlite this is sold by Home Depot. The product was originally sold as a wall panel for walk in freezers. It is usually sold as a bathroom wall panel.

West system (or other similar Epoxy adhesives) can be mixed with a filler to make a adhesive paste to bond the insulation panels and the Strutoglas panels together. When the Strutoglas is bonded to the polystyrene foam it will produce a very rigid and strong composite panel.

The panels can be bonded to one another by masking the edges of the joints and forming a fillet of epoxy and filler.

An air tight door or lid is as important as good insulation.

Gaskets should be checked and replaced if they are worn. Clean Seal manufactures a number of very high quality gaskets. We normally have several profiles in stock .