The Problem Anytime you maintain, retrofit, or replace a gas heating system you also need to be concerned with air quality. Combustion air is needed by all oil and gas heating systems to support the combustion process. This air is provided in some homes by unintentional air leaks, or by air ducts that connect to the outdoors. The combustion process creates several byproducts that are potentially hazardous to human health and can cause deterioration in your home. You can protect yourself from these hazards, as well as maintain energy efficiency, by ensuring that your chimney system functions properly and that your gas heating system is properly ventilated. In some cases, installing a sealed-combustion furnace or boiler can also help.
The Solution A general rule of thumb is 2 in2 of ventilation for every thousand BTUs of heating input for mechanical equipment. Thus, if the input of a heating system is 200,000BTUs, the appropriate dimensions for a louver would be 20” x 20“. It is important to consider all mechanical equipment in the boiler room when sizing ventilation, not just the boiler or furnace. Fig. 1: A common mechanical louver used for boiler room ventilation http://www.cntenergy.org/media/Boiler-Room-Increase-Ventilation.pdf
Special Considerations In colder climates, it is ideal to direct the outside air towards the intake of the mechanical equipment. This will ensure that less of the unconditioned air from outside cools the room and the equipment, and more is utilized to maintain the highest efficiency possible in the heating system. Regardless of climate, it is always advantageous to have a mechanical louver, which opens when the mechanical equipment needs air intake, and closes when the equipment turns off, thus keeping out unneeded ventilation to the outside. Of course, uncontrolled intake of outside air is preferable to the dangers of unventilated boiler rooms, but depending on the climate, the unconditioned air will cool the boiler room and increase fuel costs.