Abstract: This invention relates to a humidifier and associated heater. The humidifier of the present invention is for humidifying breathable gas such as air or oxygen-supplemented air to be inhaled by a patient. The humidifier comprises a body defining a humidifying chamber, a fluid inlet conduit, and a fluid outlet conduit for directing a moving stream of breathable gas into and out of the body, and a liquid collection well. A sheet of wicking material is suspended within the body and absorbs liquid in the well, exposing the liquid to the moving stream of gas as it passes through the body. The body also includes a heat exchange sleeve which extends into the collection well, the interior of the sleeve being isolated from the humidifying chamber. The heater is selectively joined to the humidifier, extends into the heat exchange sleeve and heats the humidified stream of gas as it passes through the body.