Not sure if it is free? Thought he was implying it was 15% cheaper than the utility charges. Is that due to the running cost of the air pump?
Would be great for daytime use but most of our heating requirement in SA is mornings and nights when the sun is not shining to produce heat. Guess it would need to shut down the air pump when the sun is not shining or it may suck the heat out of the room.
Great to see people inventing things so simple to help reduce the greenhouse gas emissions.