How does insulation work?

Heat flows from warmer to cooler via convection, conduction and radiation.

Heat flow through a ceiling is an example of all 3 types of heat transfer:

• Hot air in contact with your ceiling will transfer heat to it by convection.
  (The hot roof will also radiate heat into your roof space.)
• That heat will then be conducted through your ceiling.
• The hot ceiling will then radiate heat into your room.
  (There will also be convection of heat into your room.)

Bulk insulation such as cellulose works by having sufficient density to effectively prevent convection through the product but still low enough density to avoid conduction.

The optimal density of cellulose means that for a given thickness you will obtain the highest R value. Also as cellulose has a constant and low thermal conductivity for all practical installation densities and temperature differences the R value can always be verified by simply measuring the installation thickness.

Insulation with an R value does the following:-

1. Limits the flow of heat for a given temperature difference. Heat flow is energy which costs money.
   The density of heat flow rate in W/m² is given by:
   • u = (Ti - Te) / R.
     Where:
     • Ti is inside temperature in K (or °C);
     • Te is environment temperature in K (or °C); and
     • R is thermal resistance in K·m²/W.
2. The total power to heat the space in W is given by:
   • P = u·a.
     Where:
     • P is the total heat flux in W; and
     • a is the area in m².

See energy usage.

3. Maintain a temperature difference for a given flow of heat and take advantage of winter sun or other heating or cooling.
   The temperature rise in K (or °C) is given by:
   • (Ti - Te) = R·u.
4. Reduce the day to night variation in temperature, in conjunction with the specific and latent heats within the building.

See temperature variation: Q1|Q2|Q3|Q4

cellulose ... naturally
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