Combustion Ventilation Requirements

All fueled fired appliances require air for proper combustion. The following will provide you with the basic facts to understand and properly provide both combustion AND ventilation air.

Many existing local codes (pre 1985) and most longtime plumbing and heating contractors ("I've been doing this for 20 years") fail to recognize today's needs, and the reason behind those needs for proper combustion and ventilation air. While the quantity of combustion air required has changed very little, the appliance's ability to "draw" this air to it has been substantially reduced. Why? Increases in appliance efficiency result in greatly reduced stack temperatures.

This reduction decreases the draft force created on the stack (the greater the temperature difference between room air and stack temperature, the greater the stack force), making it more difficult for the appliance to draw in the combustion air and vent products of combustion. Typical stack temperatures in older equipment with efficiencies of less than 80% are in the 400*F to 700*F range. Today's appliances operate with stack temperatures of 210*F to 325*F and efficiencies of 80%-88%. As a result of this deduction in draft force, the following requirements (which have been recommended by manufacturers for over ten years) MUST BE USED for proper combustion and long life. 

For every 1,000 BTU's of input, you must provide one square inch of free area for air movement if taken from outdoors, and double that if taken from an adjacent interior space. These openings must be 1/2 near the floor level (combustion air inlet) and 1/2 near the ceiling level (ventilation air outlet). Having these two openings at different heights makes use of the natural barometric differences to create air movement within the equipment room (from floor to ceiling, and up the appliance stack). As the appliance begins a burn cycle, the increase in stack temperature will generate proper draft through the unit, providing the facility owner with the efficiency they paid for.

Many equipment owners complain about the cold air coming in to the equipment room in the winter. If you cover the combustion/ventilation openings, in your quest for a warmer equipment room, you will also receive higher fuel bills, increased maintenance, and shorter life of your equipment.

Of course, there is a way around this problem. Use equipment with sealed combustion! The intake air for combustion is connected directly to the appliance, thus eliminating the cold air in the equipment room. The V-Tube offers this venting option. Other options are to use motorized louvers or an intake air fan that only runs (or opens) during a burn cycle.