Seeber's Science: How many pages of student work would I have to burn to heat my classroom?

It might be cold outside, but science teacher Emily Seeber has some creative suggestions for getting your classroom warm (all entirely hypothetical, of course)

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The heating broke in the science department last Friday. As I’m based in a lab, when the heating goes, I usually just light Bunsen burners to warm the room up (I’m not sure the school takes that into account as part of its heating budget).

But, as I stood there rubbing my numb hands, I started thinking about what I could do if I didn’t have gas taps...

Classrooms are full of fuels. The tables and chairs, the stacks of books. Some classrooms have extra fun things to burn: pianos in the music department, cupboards of poetry anthologies in English, and I don’t need to spell out the fun a pyromaniac could have in the art and design building.

But paper is ubiquitous throughout the school. Even paper-free schools can’t seem to get away from it. So, how many pages of student work would a teacher need to burn to heat their classroom?

Judge joules

The equation used to work out how much energy is required to heat the room is Q = m x C x ΔΤ. Q is the energy in Kilojoules, m is the mass of the air in grams, C is the heat capacity of air (1 kJkg-1K-1), and ΔT is the change in temperature.

Let’s imagine that the average classroom measures 12 x 8 x 2 metres. This gives a volume of around 200 m3. This equates to roughly 250 kg of air to heat.  

My classroom was 14°C on Friday, so it needed to heat up by about 7°C for my fingers to defrost. Let’s plug these numbers into the equation: Q = 250 x 1 x 7 = 1750 kJ.

So, we need to generate 1750 kJ.

To the window, to the wall

Paper is basically cellulose, so when burned in plenty of oxygen, one gram of paper releases 15 kJ, and about 4 kJ in a limited supply of oxygen. Assuming a mix of complete and incomplete combustion, 300 grams of paper would be required. We can at least double that, taking into account heating up the walls, windows, furniture and people in the room (which have higher heat capacities than the air). Let’s say 1 kg of paper to be on the safe side.

To put that in context, each sheet of paper has a mass of approximately 5 grams, which means we would need to burn 200 sheets of paper. Imagining that each of those sheets is covered, double-sided, with student work, that’s 400 sides of work. And if students spend roughly three hours writing a four-page essay, that’s 100 essays, and 300 hours’ work.

So, if a student worked for an hour every weeknight during term time, it would take them two years to generate enough sides of writing just to get your classroom up to temperature. That’s not counting the energy required to keep it warm as heat escapes through the windows and walls.

When put into these terms, getting an engineer out to fix the heating seems like a pretty reasonable price to pay.

Emily Seeber is head of science at Bedales School in Hampshire

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