Hay Box Cooker Calculator

Calculate heat retention time, temperature curve, and fuel savings for a hay box (retained heat) cooker based on pot size, insulation, and food mass.

Food + liquid mass

Pot diameter

Starting temperature

°F

Insulation R-value

m²·K/W

Room temperature

°F

Tab to move between fields

Time above 75 °C

17.7 hours

Time above 60 °C33 hours

Temperature after 2 hours97 °C

Temperature after 4 hours93 °C

Temperature after 8 hours88 °C

Fuel savings83%

Insulation volume needed48 liters

How to Use This Calculator

Enter the mass of food plus liquid in the pot (kg) and pot diameter (cm).
Set the starting temperature (typically boiling, 100 °C) and insulation R-value.
Enter ambient room temperature.
The calculator shows how long food stays above 75 °C (safe cooking zone) and above 60 °C, plus temperatures after 2, 4, and 8 hours.
Bring food to a full boil on your stove, then transfer immediately to the insulated box for hands-free retained-heat cooking.

How the result changes with Pot diameter

Food + liquid mass: Total weight of food and liquid in the pot. More mass retains heat longer.
Pot diameter: Outer diameter of the cooking pot. Smaller pots cool faster.
Starting temperature: Temperature when the pot goes into the hay box. Should be at or near boiling (100 °C).
Insulation R-value: Thermal resistance of insulation. Hay/straw ≈ 2–3, wool blanket ≈ 3–4, sleeping bag ≈ 4–6.
Room temperature: Ambient air temperature where the hay box is kept.

Time above 75 °C: How long food stays above 75 °C — the safe active cooking zone for stews and grains.
Time above 60 °C: Time before food drops into the danger zone (below 60 °C). Food should be eaten or reheated before this.
Temperature after 2 hours: Food temperature after 2 hours in the hay box.
Temperature after 4 hours: Food temperature after 4 hours in the hay box.
Temperature after 8 hours: Food temperature after 8 hours (e.g., overnight cooking).
Fuel savings: Estimated fuel/energy savings vs. conventional stove-top cooking for a stew.
Insulation volume needed: Volume of insulation material needed for 10 cm thickness around the pot.

Identify Input Parameters
4 parameters
Food + liquid mass = 3, Pot diameter = 24, Starting temperature = 100, Insulation R-value = 3 = 5 input(s) provided
Calculate Time above 75 °C
Time above 75 °C = timeTo75Sec / 3600
17.7 = 17.7
Calculate Time above 60 °C
Time above 60 °C = timeTo60Sec / 3600
33 = 33
Calculate Temperature after 2 hours
97 = 97