Sometimes a job requires the use of a hot water unit. A hot water skid unit is one option. A hot box can be that other option. If you aren't familiar with a hot box, just think of it as a portable water heater. The same concepts that apply to a home hot water heater, apply here. Cold water enters, is heated and then released out the trigger gun or other attachment. And many times it is the cheaper alternative and will provide you with the same results.
Hot boxes are not without concern. Hot boxes and burners will require more maintenance than a cold water unit. Units will also require certain power requirements. Inadequate power will not allow the unit to work efficiently. Inefficient operation leads to excessive smoke and sooting.
Remember that if you are converting a cold water unit to a hot water unit, take care of your system peripherals like guns and hoses and hose reels. These units are temperature rated and will fail if use outside of the manufacturer's specifications. Don't assume that the hose you used for your cold water unit will be appropriate for your hot water system. And hot water burns. We want you to stay safe.
Let us know if we can be of personal assistance to discuss your particular options.