This looks like a nice warm spot for Romeo.

Imagine it is a cool winters day. The sun is shining, but, our cat, Romeo is rather cold. Where does he go? He finds a nice spot in the sun. This is the simplest aspect of heating your house with the sun. You might say it is rather obvious but houses really aren’t designed to make the most use of this simple idea.

One of the latest books we have read in our quest for knowledge has been “The Solar House” by Daniel Chiras, about ‘passive solar’ heating and cooling. If you don’t know what a ‘passive solar‘ house is don’t worry because you aren’t alone. It is a term that is relatively new to us but if you are looking to design or build a house, some day, it is something worth knowing about.A passive solar house is a one that predominantly uses the sun for heating and cooling. This doesn’t mean that you use a solar panel to run your air-conditioner!

To help us explain what passive solar means we would like to introduce our beloved kitty, Romeo. (Cats know a lot about these things!)

If you think about how the sun moves across the sky we all know the sun goes from east to west. Most of us have rectangular houses so it makes the most sense to orient your house east to west. This means that the sun hits the long edge of your house for the longest possible time each day so you can make the most of its free heat.

You should orient the long side of your house from east to west to make the most of the sun’s warmth.

Now imagine the sun is starting to go down. The spot in the sun is gone and Romeo is still cold! Where does he go next? He seeks out a rock or brick path that has been in the sun all day. The rock and the bricks have soaked up the sun’s heat throughout the day and are now radiating that warmth back out – straight into Romeo’s cold body.

During the day the rock soaks up the sun’s heat. When the sun goes down it releases this stored heat back out into the air (or a kitty).

We can also use this when we are designing a house. If we put something like a rock that soaks up heat (like a tile floor, concrete slab, or a brick wall – this is called thermal mass) in a position that gets a lot of the sun during the day, it will radiate it’s heat back into the house at night. Voila! Free heat!

What about when it is hot in the summer? Romeo isn’t cold now – he wants a cool place to sit. I bet he would like a spot on a cool laundry or bath room floor with a bit of draft for some added cooling – a place that is probably quite far from any sunny windows.

This a similar idea to the previous one with the rock storing the heat. This time we want our thermal mass to stay as cool as possible so it can suck up the heat in the air that comes in from outside, and radiate the cool back into our house. In order for this to work we need to keep it out of the sun. The easiest way to do this is with some careful planning.

In Winter the sun enters the window and is able to heat up the thermal mass in the floor but in summer the roof overhang stops it – keeping the thermal mass cool.

In winter the days are much shorter, this is because the arc the sun makes across the sky is much lower. This means that the sun is coming in through the windows and hitting our thermal mass. In summer the sun traces a much higher arc, giving us longer days – the sun is closer to directly overhead. The easiest way to stop the sun heating up our thermal mass is by putting an overhang on the roof or over the windows. If you plant deciduous trees in front of the windows they will provide shade in the summer but will let the sun through in winter when they lose their leaves. This way the sun can enter in winter but is kept out in summer. Free heating AND cooling!

These few considerations seem so simple to us and yet they are so overlooked. Of course there are more ways to use the sun and these examples require some thought to put into practice but we really think it is worth it. There is so much information on the Internet about the basic principles but if you seriously want to know the nuts and bolts you should get a book about it. “The Solar House” by Daniel Chiras is a good one. It explains all the basics and then goes into detail about how to actually work everything out. Give it a look!

P.S. If you a looking for a new pet. ADOPT! We adopted Romeo from Save-a-Dog in Melbourne and he is the most amazing cat. We cannot wait to get back to Melbourne to give him a hug!