The arrival of cold weather needn't halt concrete construction. In moderate cold, protective systems such as insulating blankets and temporary shelters usually provide enough cold-weather protection. In severe cold, however, contractors often need to use portable heaters to maintain proper temperatures. There are two main types of heaters - fuel-fired and electrically powered. Heater models come in a range of sizes to meet different jobsite conditions. To determine the best type of heater for your needs, evaluate the following criteria: * Heating capacity, expressed in British thermal units (Btu) * Utility of both the energy source and the heater * Energy availability and storage * Portability * Safety features