A few indicative values of emissivity of materials used to transmit heat in the context of heating:
- ε (anodised aluminium) =0.77
- ε (polished aluminium) =0.05 (the surface being therefore a significant non-negligible part)
- ε (glass) =0.93
- ε (smooth metal) =0.25
- ε (metal coated with specific emissive powder to maximise the emissivity) =0.96 – sources www.degxel.co.uk
In clear terms, when we talk about the diffusion efficiency of radiation by a heater, the knowledge of the material is not sufficient to draw a conclusion. Other factors described above are essential.