A new more insulated and faster responding plate thermometer (PT) is introduced, which has been developed for measurements particularly in air at ambient temperature. It is a cheaper and more practical alternative to water‐cooled heat flux meters (HFMs). The theory and use of PTs measuring incident radiation heat flux and adiabatic surface temperature are presented. Comparisons of measurements with PTs and HFMs are made. Finally, it is concluded that incident radiation in ambient air can be measured with HFMs as well as with the new insulated type of PT. In hot gases and flames, however, only PTs can be recommended. At elevated gas temperatures, convection makes measurements with HFMs difficult to interpret and use for calculations. However, they can be used in standard or well‐defined configurations for comparisons.