Injection of mock radio halos in the cluster A220. Left: original image. Middle: injected radio halo with flux density of 7 mJy. Right: injected radio halo with flux density of 2.5 mJy. Contours start at 2-σ rms noise. The two circles have radii of 2.6 × r_e = 500 kpc and are centred on the cluster centre (yellow) and on the modelled radio halo (magenta). We consider 2.5 mJy to be the upper limit to the diffuse emission of A220.