HVAC chemicals treatment

what about sodium nitrit in HVAC system

Sodium nitrite is used as an oxygen scavenger.

Sodium nitrite, generally combined with borate for pH control and azole for non-ferrous metal protection, has been a staple of the water treatment industry for many years. Nitrite provides good corrosion protection when maintained within the optimum levels, usually 800 to 1200 ppm NaN0₂, but actually increases corrosion when maintained at levels below 500 ppm. Higher concentrations of this product, mainly because of the resulting higher pH, have been found to cause pump seal damage. Nitrite is also a contributor to bacterial growth within the system, and should be replaced with a non-nitrite product if bacteria is encountered. Antimicrobial agents are also often used in conjunction with closed system inhibitors; but must be products formulated and labeled for use in hot water recirculating systems.