Heavier oils number 4, 5 and 6 are preheated to ______ :

Air is forced into the combustion chamber by ______ fan or blower to maintain a positive pressure in boiler:

______ boilers are used extensively for comfort heating applications:

A _______ fuel oil to air ratio causes sooting and low burner efficiency:

Operation of the boiler or furnace with excess air by 10% may reduce boiler efficiency by about _______ :

A layer of soot or scale having 0.18 inches thick can reduce heat transfer by:

All oils are converted to vapors before they burn

The heating capacity of electric heating systems is usually expressed in which of the following units