What water temperature rise is acceptable across an injection mold?

Autodesk Moldflow advises no more than 2 to 3 °C from inlet to outlet. Higher values can mean a wider mold surface temperature range, which Moldflow says is of primary importance. Use the moldmaker's limit if the tool has one.

My outlet reads colder than the inlet. What does that mean?

The water is giving heat to the mold instead of taking it away. That is normal while a mold warms up on hot water. In steady production, check for swapped thermometers or hoses first.

How can I measure circuit flow without a flow meter?

Time how long the circuit's return takes to fill a container of known volume, then divide liters by seconds and multiply by 60 for L/min. Take the reading at normal supply pressure.

Can I use the heat figure to size a chiller?

Yes, for the mold's share: sum the kW of every circuit to get the heat the mold rejects to water, then add the other loads on that chiller. The sum is also the heat load for sizing mold flow.

Injection Molding calculator

Mold Temperature Delta Calculator

Find whether the water temperature rise across one cooling circuit is within your limit, and the flow that would fix it. You need inlet and outlet temperatures at steady state and the circuit's flow.

What this calculator does

Water temperature rise across one mold cooling circuit, the heat it carries, and the flow that holds the rise within your limit.

Formula used

Rise (°C) = outlet temperature − inlet temperature
Heat carried (kW) = flow (L/min) ÷ 60,000 × ρ (kg/m³) × cp (kJ/kg·K) × rise
Flow for the allowable rise (L/min) = flow × |rise| ÷ allowable rise

Inputs explained

Water Inlet Temperature: Supply line at the mold, same thermometer type as the outlet.
Water Outlet Temperature: Return line at the mold, once the process is at steady state.
Circuit Water Flow: Flow meter or regulator reading for this one circuit.
Allowable Water Temperature Rise: Outlet minus inlet; Moldflow advises no more than 2 to 3 °C.

How to use the result

Best suited to qualifying cooling on a new mold, finding a starved circuit on a running mold, checking flow after descaling cooling lines.
A small rise at a shared return can hide one hot, starved branch; measure parallel circuits one at a time. Probe error counts fully: a 0.5 °C reading error is a sixth of a 3 °C limit.

Current U.S. benchmarks

The producer price index for plastic resins and materials stands at 280.569 (BLS, Aug 2026), up 6.6% from a year earlier. Quotes priced off last quarter's material cost miss this move.
The U.S. has 9,635 plastics product manufacturing establishments employing about 677,302 workers (Census County Business Patterns, 2023).

Common questions

What water temperature rise is acceptable across an injection mold? Autodesk Moldflow advises no more than 2 to 3 °C from inlet to outlet. Higher values can mean a wider mold surface temperature range, which Moldflow says is of primary importance. Use the moldmaker's limit if the tool has one.
My outlet reads colder than the inlet. What does that mean? The water is giving heat to the mold instead of taking it away. That is normal while a mold warms up on hot water. In steady production, check for swapped thermometers or hoses first.
How can I measure circuit flow without a flow meter? Time how long the circuit's return takes to fill a container of known volume, then divide liters by seconds and multiply by 60 for L/min. Take the reading at normal supply pressure.
Can I use the heat figure to size a chiller? Yes, for the mold's share: sum the kW of every circuit to get the heat the mold rejects to water, then add the other loads on that chiller. The sum is also the heat load for sizing mold flow.

Last reviewed 2026-10-01.