Pick the glycol and the coldest temperature the loop can see. The page gives the concentration with a safety margin, the solution properties and how much flow, pressure drop and pump power rise compared with water.
Pre-sizing and estimating tool: results do not replace design, calculations or reports signed by a licensed professional, nor verification against the applicable codes and standards.
Inhibited ethylene and propylene glycol, as % of solution volume.
Same heat load and temperature difference; 100% = value with water.
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Enough for the solution to freeze a few degrees below the coldest temperature the loop can see. In the example, for a 14 °F minimum with a 5 °F margin, ethylene glycol needs 25.7% by volume (27.9% by mass), freezing at 9 °F. More glycol than needed only adds viscosity, pump energy and cost.
Ethylene glycol transfers heat better and is less viscous, but it is toxic; propylene glycol is the choice where food, beverages or potable water could be contacted. For the same protection, propylene glycol needs a little more concentration (29.5% versus 25.7% in the example) and more pumping energy. Either way, use inhibited industrial glycol, never automotive antifreeze.
The solution has a lower specific heat than water, so each gallon carries less heat and more flow is needed for the same load: in the example, 260 gpm instead of 239. It is also about twice as viscous in the cold, which increases friction. The result is 29% more head and 47% more pump power, about $1,240 a year in the example.
If flow stays the same, heat-carrying capacity drops at least 8% in the example, and coils and exchangers also perform worse. The existing pump may deliver less flow because of the higher loss. Check the pump, the heat exchangers and the expansion tank before switching fluids.
Yes. Below about 25% to 30% by volume, corrosion inhibitors get too diluted and the solution can even feed bacterial growth, so the page uses 25% as the default minimum. Check the exact value on the product data sheet.
They are typical values for commercial inhibited glycols from manufacturer tables, interpolated by temperature and concentration; above 50% and outside the tabulated range they are extrapolated. Other makers’ products can differ by a few percent. The friction correction uses one representative pipe and is an estimate for the whole loop.
With a glycol refractometer, or by measuring density and comparing with the manufacturer’s table. A yearly fluid analysis (concentration, pH and inhibitor reserve) is recommended, because topping up with plain water dilutes the glycol over time.
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