Abstract: A fully removable heating element assembly for use in fluid heaters and boilers, such as the boiler contained in a CO.sub.2 removal air purification system employing a monoethanolamine (MEA) solution, includes a rectangularly shaped housing open on a rear end thereof. An oversize cover plate connected to and covering an open front end of the housing is connectable to an opening in a fluid boiler. A series of elongated hollow tubes, each of which tubes is closed on its forward end and open on its rear end, are connected on rear end portions thereof to the plate so as to project forwardly of the housing into the interior of the boiler. A like series of electrical heating elements are slidably and removably inserted into the tubes and have rear end portions containing pairs of electrical terminals which project rearwardly of the plate and are confined within the housing.