Interactive lesson

The ice house, step by step

Interactive lesson: how to keep winter ice until August — insulation, drainage, where the ice comes from, building, filling, the icebox and safety on the pond.

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The whole lesson as text

1. How an ice house works

An ice house does not make cold. It only slows down the melting of winter ice.

A block of ice — Ice is a store of cold. While it melts, food next to it stays at 0–4 °C (32–40 °F), enough for meat, milk and leftovers.
Sawdust on all sides — Between ice and wall goes 30–45 cm (12–18 in) of dry sawdust, and 40–60 cm on top. Wet sawdust hardly insulates at all.
A drain under the ice — Water is the worst enemy. It must run away at once through gravel and a pipe with a trap, so warm air does not come in from below.
Shade and air above — The ice house stands in shade, under a pale roof. Through vents in the gables, warm air under the roof escapes instead of warming the ice.

Why: While ice melts it stays at 0 °C and absorbs a lot of heat: a kilogram of ice cools 4 kg of water from 20 to 0 °C. Heat reaches the ice from the ground, the sun, warm air and water, and each side has its own protection.

A big block lasts longer: a 2 m cube holds eight times as much ice as a 1 m cube, but has only four times the surface.
Below roughly 1.5–2 m³ of ice, an ice house rarely lasts until August.

2. Where the ice comes from

A pond gives the most ice; moulds of drinking water give ice for drinks.

Pond ice — The most ice for the least work. It is only for indirect cooling, round sealed containers, never in drinks or on food.
Moulds of drinking water — Leave buckets and troughs of 10–25 L filled with well or mains water outside on frosty nights. A 20 L bucket freezes through in roughly 3–6 frosty days.
Drinking ice, wrapped — Wrap blocks of drinking water in clean film or a heavy bag before stacking. Without a bag, in the sawdust, they are no longer fit for direct contact with food.
Packed snow — When there is no ice, pack snow in layers. It has roughly half the density of ice, so for the same cold you need twice the space.

Why: Freezing does not clean water. Bacteria, parasites and chemicals from a pond survive in the ice and return to the water when it melts.

Fill a mould three-quarters full, because ice expands. Buckets with slightly sloping sides release the block more easily.
In lowland Britain and Ireland natural ice is rare: there the icebox runs on ice from a freezer on surplus solar power or from moulds in a cold snap.