Low oil prices have motivated development of lower cost recovery processes for production of heavy oil and bitumen. Electrical heating using heaters has been proposed recently to not only lower costs, but also improve energy efficiency and reduce environmental impact compared to current thermal recovery methods such as steam assisted gravity drainage. Elimination of steam injection from bitumen recovery processes greatly decreases the capital and operating costs of oil sand development projects and also minimizes the environmental footprint of bitumen production. One of the challenges faced during electrical heating of bitumen formations is desiccation of the formation around downhole heaters at high temperatures resulting in reduced heat delivery to the reservoir. This problem can be eased by injection of makeup water or solvent to add a convective heat transfer element to the otherwise mainly conductive heat transfer from the heater to the formation. In this paper a simple analytical model is presented that allows estimation of the rate of makeup water or other fluid required for efficient heat delivery to the bitumen bearing formations. The effects of formation porosity, rock type and fluid saturation on heat transfer are also evaluated. (C) 2016 Elsevier Ltd. All rights reserved.