Heating one’s home is a deceptively difficult thing to do, despite the modern conveniences on which we have come to rely. Science describes the various ways in which the movement of air and energy can cause the wicking of thermal energy from domestic spaces, and the various systems we use to insulate our homes ever-more efficiently – but another form of difficulty has emerged, in the form of cost.
Global instability and national barriers to trade have seen energy bills rise for millions of households in the UK, and rendered all the clearer the importance of energy-efficient homes. To understand a home’s energy efficiency prospects, we need to understand where heat escapes.
One of the most well-known properties of heat is that it rises. Strictly speaking, though, thermal energy itself doesn’t rise, but rather hot air rises. This is because molecules in the air move faster and farther apart, resulting in a less dense gas that rises and displaces colder, denser air above it.
It stands to reason, then, that a significant portion of heat in the home is lost through the roof. Roof insulation has been a vital constituent part of domestic construction for hundreds of years, today taking the form of fibreglass and mineral wool rolls or sheets. These form a barrier for heat transfer into the attic compartment, forcing warm air to remain in the home.
But rising hot air is not the only component of heat less in the home. Heat conduction also takes place, wherein heat is transferred directly through material instead of through air movement. Your home’s walls constitute the largest proportion of its surface area, and can act as conduits for thermal energy to pass through.
Cavity walls were invented to mitigate the impact of this, and cavity wall insulation invented to dramatically improve the efficacy of cavity wall structures. In a given property, cavity wall insulation is so efficient that energy savings near-universally outweigh installation costs in five years or fewer.
Of course, the windows installed in your walls are a weak spot all of their own. Where bricks and breeze-blocks offer some level of insulation owing to properties including their aeration, window panes are more perfect conductors of thermal energy, and make it much easier for heat to leave. Secondarily, the seal around the window frames can be imperfect, allowing for draughts.
Double-glazed windows are the modern industry standard for new build properties, and for renovating older properties. It works in a similar way to cavity walls, but more effectively; two glass panes are used, and separated by a vacuum. The vacuum cavity makes it extremely difficult for heat to transfer out, as no particles exist to pass it on. Triple-glazed windows also exist, exhibiting higher insulative resistance as well as noise resistance.