Heating I notes

1. Roughly 10 cubic feet of air are needed to burn every one cubic foot of gas, under perfect combustion circumstances. In reality, there is always more air provided than is required for perfect cumbustion. The excess air is typically about 5 cubic feet. Generally speaking, 15 feet of cubic air is provided for every cubic foot of gas burned.
2. A cubic foot of natural gas contains about 1000 BTUs, a furnace that fires at the rate of 120, 000BTUs per hour, would use 120 cubic feet of gas if it fired constantly for 60mins.
3. There is another 15 cubic feet of air required as draft air. So for a conventional gas furnace, roughly 30 cubic feet of air for every cubic foot of gas burned, that is 1000BTUs.
4. For every 1000 feet above sea level, the fire rate should be decreased by 4%. I.E. We have a furnace that has fire rate 138,000BTU/hour, and the location of the furnace is 5000 feet above sea level. The actual fire rate is 138,000 * 0.8 = 110,400BTU/hour