As fluids heat up, they expand, and every heat transfer system needs to accommodate this increase in volume. Expansion tanks serve exactly this purpose—providing space for the fluid as it expands. But how do you figure out the right tank size?

The first step is to calculate the Delta T, which in this context is simply the difference between your starting temperature and your target system temperature. That number is then multiplied by the fluid’s coefficient of thermal expansion.

For example, if your fluid is being heated from an ambient temperature of 70°F to 300°F, the Delta T would be 230. Using Duratherm 450’s thermal expansion coefficient of 0.0564%/°F, the formula would be:

• (300°F – 70°F) x 0.0564 = 12.972 (expressed as a percentage)

Now let’s assume your system capacity is 100 gallons. Based on the calculation above, the expanded volume would require about 13 additional gallons, bringing the total to 113 gallons. That means your expansion tank should be able to handle that extra volume.

One last consideration: as a general rule, expansion tanks should be about one-third full when the fluid is cold and roughly one-half full when hot.

We hope this explanation helps, but if you have questions or need clarification, please reach out.