Why is everyone putting propane in their heat pumps?

Photo: Shutterstock: Deyan Georgiev

Graham Hendra ponders R290, the wonder gas that manufacturers are rushing to get into their heat pumps.

In the last 12 months all the good heat pump manufacturers have produced a unit with the new wonder gas R290 inside. Why?

Using R290 refrigerant in heat pumps is now common because it has one great feature: If it leaks into the atmosphere, it has a low global warming potential. It is only three times as bad for global warming as CO2. The refrigerant it replaces in most heat pumps, R32 is 677 times as bad as CO2, so you can see why it had to go. You think that is bad? Only a couple of years ago we were using refrigerants which were over 2000 times as bad as CO2.

R290 is cheap, readily available, nontoxic, low pressure and easily transportable, but it has one bad feature. The gas, more commonly known as propane, burns like hell. That’s why you will probably be using it in your barbecue.

Propane also has a few other more geeky benefits:  Its relatively low pressure at 0 deg C is only 3.7 bar, and at 60 deg C it is only 20 Bar – that’s half the pressure of the refrigerant it replaces, so leakage is much less likely.

We don’t need much of it in our heating systems either: a typical 14 kW heat pump will contain 1.25 kg of Propane. By comparison, a 14 kW heat pump using R32 would need 3.3 kg of the gas.

Putting all this into CO2 emissions terms, if the new R290 unit leaks, it is equivalent to 0.00375 tonnes of CO2 being released. The old unit was equivalent to 2.23 tonnes. In plain in English the old unit is 594 times worse if it leaks than the new one. So now you know why everyone wants to use R290.

But if it does leak, isn’t there a fire risk? I hear you asking.

In short, yes: If you are stupid enough to approach a leaking R290 system, Zippo in hand and try to light up, you are going to lose your eyebrows.

This simple fact means there is bound to be some scaremongering around. So let’s put it into perspective:

The R290 is all going to be outside, in the garden – none of it is allowed anywhere near the inside of the house. If it leaks, it will dissipate in the wind. My barbecue bottle has 9 kg of R290 in it. But I don’t keep it by the bed – it lives in the shed, with the petrol cans and the Moonshine.

You need more perspective: This morning when I got up, I put on my deodorant, used some dry shampoo on my hair and applied liberal amounts of my favourite hair spray [feel free to guess what it is…]

Each of these cans, which I keep by my bed, contains 200 grammes or 0.2 kg of R290. So, yes, I am effectively sleeping next to three small barbecue gas cans and I happily spray this stuff all over myself every morning and I’m still alive.

All things considered, I would suggest that smoking while applying hair spray is considerably more dangerous than installing an R290 heat pump in the garden.

And there is one more thing I forgot to mention about R290: it has a party piece. Its chemical properties meant that an R290 heat pump can heat the water in your radiators and cylinder to an impressive 80 deg C. So it’s like an eco-friendly boiler…only hotter.