Heat Transfer

In my second podcast, I discussed heat transfer and the the types and styles of insulation. I talked about ‘R-value’ and the technical meaning of thermal resistance.

Well, without a full transcript (or even detailed show notes at this stage), I thought it might be worth doing quick follow-up entry with some of the content.

My first reference is to Wikipedia. With so much of the insulation world online taken up with people trying to sell the stuff, I’ve found Wikipedia to be an excellent source or unbiased, scientific information about what exactly insulation is and how it works.

Heat Transfer

To understand why and how insulation works, we need to briefly step back into basic physics and look at heat transfer. This is because we use insulation to slow down heat transfer, so it’s a good idea to fully understand how heat flows in the first place.

Heat moves in three basic ways:

  • Conduction: When one end of something like a metal rod gets hot, the other end will eventually also get hot as heat is conducted through the material.
  • Convection: ‘Hot air rises’. This makes air move around in enclosed spaces (e.g. inside your lounge room). The moving air then moves the heat around as a ‘convection current’ is formed in the room. Not that this can lead to draughts as cooler air moves in to replace the warm air rising off a heater.
  • Radiation: This is the good stuff, particularly for us humans with lots of hairless, fur-less skin. We love the feel of direct warmth from the sun, a blazing fire or the glow of an electric element. This type of heat movement tends to be the quickest as it relies of the direct transfer of heat energy in the form of radiation.

I also add a fourth one in there for households:

  • Draughts: This is not a fundamental method of heat movement in pure physical terms. It’s simply the movement of air through cracks and openings in our homes. Draughts are very important in practical terms for two reasons. Firstly draughts contribute to significant overall heat loss, particularly in older homes or in houses with lots of holes. Secondly, draughts are important because if they’re bigger enough to feel, they make a big impact on our discomfort. And the whole idea here is to feel comfortable in our homes.

So, armed with this knowledge of how heat actually moves, we can then go on to look at home to reduce this movement in places where we wan to reduce it, such as our ceilings, walls, floors and all the necessary holes in our walls like windows and doors.