Furnace Air Flow Requirements

Although we cannot control the loss of air we can properly diagnose.

Furnace air flow requirements.

Natural draft furnaces 100 cfm per 10 000 btu of rated btu input induced draft furnaces 130 cfm per 10 000 btu of rated btu input. If the supply ducts are in the floor then the return air should be located up high. This is called ventilation air. L air flow rate m 3 s q heat loss covered by the air heating system kw c p specific heat air 1 005 kj kg o c ρ density of air 1 2 kg m 3 t h heating air temperature.

Divide the rated btu by 10 000. It s great on a flat stretch of road but takes a lot more energy to go up a steep hill. Gas fired furnaces start with the rated btu input of the furnace. When this outside air is drawn into the structure while the furnace is operating in the heating mode the air that s coming is a going to be cold.

Single stage models are like a bicycle with one gear. And that means that we need to account for that additional load on the furnace when it s sized so that it will be able. To find required airflow divide the rated furnace input by 10 000 btu. L q c p ρ t h t r 1 where.

This airflow rule is applied to determine furnace airflow for three types of furnaces. Multiply that figure by the factor form the table below depending on the type of furnace to find required system airflow. This air is used in combustion and as a re placement for the air that a modern home loses through outward flow due to mechanical ventilation. Supply air from furnaces and air conditioners should be on outside walls.

Required air volume in an air heating system. Think of heating stages as gears on a bicycle or a car. Jim johnson december 22. 100 000 divided by 10 000 equals a factor of 10.

Required air flow rate in an air heating system can be calculated as. We will also learn that a gas furnace requires a substantial amount of fresh air to operate properly. In milder climates with lower annual heating costs the extra investment required to go from 80 to 90 to 95 efficiency may be hard to justify. Fresh air requirements and furnace operation.

The return air vent openings need to be on the opposite side of the room so the conditioned air is pulled across the room. Today s forced air furnaces are available in single stage two stage or multi stage models. 10 times 130 cfm equals 1300 cfm. If the furnace is putting out 1 000 cubic feet per minute of air flow the return system must collect 1 000 cubic feet and take it back to the unit.

An insufficient return system or one too large will reduce the efficiency of the heating and increase energy bills.