If your heating system is in need of antifreeze you need to add only the amount required. Do not add more than needed. When adding antifreeze there is a possibility you may need to increase the pump size and/or expansion tank size. The more you add the better the chance of possible up sizing these items. After adding antifreeze you will find leaks that did not exist with just water in the system. Do not exceed 50% without the manufacturer's OK.

In most systems you can use polypropylene glycol in cast iron, steel, and stainless steel boilers. If you have cast aluminum you must use antifreeze that is suitable for aluminum.

When antifreeze is installed in the system the percentage is determined by the water volume in the system. You need to calculate the water volume in the system and boiler. Pipes of different sizes will hold different amounts of water. Use the charts below to determine system water volume and add the boiler water volume to it. The charts are for piping and cast iron radiation. For finned tube radiation, just count it as pipe.

Radiation Water Volume