What process is used to separate oxygen and other noncondensable gases from feedwater?

The process used to separate oxygen and other noncondensable gases from feedwater is ventilation. This technique involves the removal of dissolved gases from the water, primarily through the introduction of air or through vacuum processes. When the feedwater is subjected to ventilation, the noncondensable gases escape from the liquid due to the difference in pressure and concentration, thus purifying the water before it enters the boiler.

The other options do not appropriately address the separation of gases. Heating can increase the solubility of gases in water and may not be effective at removing them. Cooling could potentially lead to condensation, but it does not specifically target the removal of noncondensable gases. Filtration is generally used to remove solid particulates rather than gases, making it unsuitable for this particular process.