No, unfortunately, you cannot apply fire to the InfuSsion Mash Tun. Just like a plastic cooler, This vessel is foam insulated - you can't apply flame to the bottom directly. This will melt the insulation and your mash tun will not hold heat much better than a regular kettle.
Induction also is not effective on the InfuSsion Mash Tuns, as they do not have a flat, triclad bottom designed for Induction heating. Even if it did, this would not work well with the center drain port and would need to waste a lot of electricity in order to get any sort of results.
What about submerging an electric heating element in your InfuSsion Mash Tun? Probably not. While the InfuSsion Mash Tun is capable of withstanding temperatures of near-boiling water, the heating element can reach temperatures far beyond boiling temps. An element inside the InfuSsion Mash Tun can easily come in contact with the sidewall and cause damage to the insulation, even if the liquid doesn't rise to boil temps. This is why we do not recommend electric heating elements directly in the Infussion Mash Tun. They are better off in a separate housing like in a RIMS setup.
Check out the link below for heating options that DO work for the InfuSsion Mash Tuns!