This section is from the book "A Treatise On Architecture And Building Construction Vol4: Plumbing And Gas-Fitting, Heating And Ventilation, Painting And Decorating, Estimating And Calculating Quantities", by The Colliery Engineer Co. Also available from Amazon: A Treatise On Architecture And Building Construction.
In both systems the power employed to move the air is derived from heat. In the former system it is applied to the air directly to expand the air and reduce its weight, so that the colder and heavier atmosphere will displace the warmer air and drive it through the flues, as desired. In the latter system the heat is first converted into mechanical power through the agency of a boiler and engine, and is then applied to moving the air by means of a fan. Of course, the conversion of heat into power is attended with considerable loss; but, after making all proper allowances for imperfections of machinery, etc., it is found that, in order to move a given quantity of air, the former system requires about one thousand times as much heat as the latter.
The mechanical apparatus usually employed for moving air in large quantities, at the low pressure required for heating and ventilation, consists chiefly of steam-jet blowers and fa/is.