What Is a Solar Chimney and How Does It Work?

In the course of my research into all things air-conditioning I came across the phrase ‘solar chimney’ quite a few times.

Being the inquisitive (nosey!) person that I am I wanted to find out more.

What exactly is a solar chimney?  How do they work? What benefits do they have? And just what is the connection to air conditioning?!

Well, it turns out that a solar chimney – also known as a thermal chimney, thermosiphon or thermosyphon – is a passive, non-mechanical and non-electrical way of generating cool air in buildings, including homes and offices.

It’s a well-known fact that hot air rises, and through the principles of convective cooling a solar chimney works by expelling hot air out at the top and drawing cooler air back in at the bottom.

There’s evidence to suggest that solar chimneys were first used centuries ago, by the Romans in Europe and the Persians in the Middle East.

Harnessing the Power of the Sun to Cool Things Down

In their simplest form they consist of a vertical stack (chimney) which is painted in a dark, matt colour, usually black as this is the most effective at absorbing solar radiation.


Throughout the day in the glare of the sun’s rays the chimney gets hot, in turn heating up the air contained inside it. This hot air rises to the top of the chimney and is vented out through an exhaust outlet.

As this happens an updraft pulls cooler air from the outside in at the bottom of the chimney via a series of inlets, and this suction effect helps to ventilate and cool the building below.

Solar chimneys are particularly useful in hot and humid conditions where there is very little wind. And as the name ‘solar’ suggests, generous exposure to the sun is crucial to their effective operation.

It’s also important that they’re properly insulated from the buildings they occupy so that heat doesn’t get transferred back to the very space that needs to be cooled.

Multi-Tasking in All Climates

That said, solar chimneys can actually also be used to warm up spaces when the weather turns colder.

In such cases the exhaust outlet at the top isn’t left open, but is instead closed. At the same time interior vents are opened, which transfers the hot air back into the building – a clever but effective form of convective central heating.

pros and cons, for and against argument conceptAdvantages of a Solar Thermal Chimney

1. Less Impact on the Environment

Despite the name, these type of ‘chimneys’ don’t actually omit smoke or other noxious fumes like a traditional chimney – it’s purely hot air which is being expelled.

Carbon dioxide emissions are minimal, and there’s significantly less noise pollution than conventional air conditioning units which can sometimes generate a fair bit of background noise.

2. Cost-Effective Cooling Power

Of course, there will be some initial capital outlay involved in the construction of a solar chimney, but once completed it operates using free solar energy and doesn’t need any electricity or gas to power it, unlike traditional AC or heating units.

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3. Reliable and Easy to Maintain

As solar chimneys are non-mechanical they’re not really susceptible to breakdowns and malfunctions, and not at the mercy of any power outages or issues with supplies of gas and electricity. All that’s really needed is a good dose of sunshine!

They’re also fairly low-maintenance and easy to keep clean, generating lower levels of dirt and grime as they don’t require fuels to function.


In conclusion, as we’ve seen from above, solar chimneys can offer some natural relief from the searing heat.

They’re one option to bear in mind when considering which method of cooling will work best for your own space, or when you’re designing a new home or undertaking a major remodelling activity.

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