As the cold weather arrives, we frequently start closing doors in and around our boiler room.
This blocks off the needed combustion air to the boiler. The required make-up air opening is:
5 square feet per 1,000,000 BTU’s per hour.
A 300 BHP boiler would require: 300 * 33,000 /1,000,000 * 5 = 49.5 square feet
THIS IS 49.5 SQUARE FEET OF UNRESTRICTED AIRFLOW
If the air make-up opening is restricted (which it always is), with louvers or screens, then a larger opening is required.
Typical devaluation factors caused by these restrictive devices are 40 to 70 percent.
So, the required opening of 49.5 square feet can approach: 49.5 / (100% -70%) = 165 square feet.
Since the cold weather places a larger load on boilers, it becomes more vital that we monitor boiler efficiency closely.