Understanding your home: Heat Flow

The basics of the performance of your home

We count upon our homes to be strong and durable. We expect them to provide us with shelter and keep us comfortable all year round. All aspects of our home has to work together to keep us comfortable. This guide is all about understanding how your home works to be able to retrofit it to perform better.

What is a building envelope?

The building envelope is the outside structure of the home. It comprises of the foundation of the home, flooring, walls, ceilings, roof, windows and doors. The building envelope helps in protecting the indoor environment from the weather outside. To maintain the comfortable temperature of our indoor environment, the building envelope must be able to control the heat flow and moisture accumulation from the inside to the outside.

The Building Envelope and heat flow

Heat moves to wherever there is a variance in temperature. Hot air rises so it is okay to assume that most of the heat loss will be through the ceiling, but this is not true. Heat will move in any direction, up, down, left or right anywhere it can go from a warm spot to a cooler spot.

Heat flow

Heat will flow in 3 distinctive ways –

Conduction – In this way, heat will transfer directly from one part of the object to another part by the molecules bumping into each other. Some materials conduct heat better than others, depending on its structure. Insulation is structured in a way that it reduces heat flow with tiny air pockets that are relatively poor conductors of heat. 

Convection – Fluid or even just movement of air can transfer heat by the convection method. In an uninsulated wall space air will pick up the heat from the warm side of the wall and then transfers it to the cold wall where it will lose the heat.

Radiation – Any object can radiate heat in the same way a fire radiates heat. When you are standing in front of a window you will radiate some heat to the window hence, you will feel cold even though the temperature in the room is warm.

In most of homes radiation accounts for less than 10% of heat loss and most of that loss is associated with windows. Conduction and convection are the main causes of heat loss in a home. Conduction usually happens through the walls. Radiation happens when the home is leaky.

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