ZigBee and Wi-Fi channels both exist in the 2.4 GHz band, existing in the exact same frequency space. When deploying both Wi-Fi and ZigBee in the same environments, careful planning must be performed to make sure that they don't interfere with each other.
Operating a ZigBee network and a Wi-Fi network on the same frequency will cause them to interfere with each other. Usually, the ZigBee network will take the hit.
ZigBee and Wi-Fi Channels
ZigBee and Wi-Fi channel numbers may seem similar, suggesting that they won't overlap. Unfortunately, this is not the case.
2.4 GHz Wi-Fi Channels
2.4 GHz ZigBee Channels
Wi-Fi's three non-overlapping channels (1, 6, and 11) use the exact same frequencies as ZigBee channels 11-22.
ZigBee channels 25-26 aren't immune either, because they can be caught in Wi-Fi channel 11's sideband lobe (see Sideband Lobes below). ZigBee channel 26 is usually relatively unaffected by Wi-Fi, but many ZigBee devices do not support it.
When a Wi-Fi network is on the same channel as a ZigBee network, the Wi-Fi network will usually interfere with the ZigBee network.