How will this do in 800 sq ft garage sprayed with foam insulation?

In a 800 square foot space a 40,000 BTU heater is recommended. This heater will work in a well insulated garage like yours but we would recommend a larger heater to heat the whole space efficiently. Please reference our Sizing Guide that will allow you to know exactly what kind of unit you'll be needing as there are many determining factors such as insulation quality, location, etc... If you have any further questions please feel free to give us a call! Thanks.