Enter System Inputs
Example Data Table
| Scenario | Load (BTU/hr) | ΔT (°F) | Fluid Constant | Flow (GPM) |
|---|---|---|---|---|
| Office heating loop | 120000 | 20 | 500 | 12.00 |
| Radiant floor zone | 48000 | 15 | 500 | 6.40 |
| 30% glycol circuit | 95000 | 18 | 475 | 11.11 |
Formula Used
Primary flow formula: Flow (GPM) = Load (BTU/hr) ÷ (Fluid Constant × ΔT).
Velocity check: GPM = Velocity × Pipe Area × 448.831.
Total head estimate: Total Head = (Head Loss per 100 ft × Equivalent Length) ÷ 100.
Pressure drop: PSI = Head × 0.433 for water-based systems.
The fluid constant reflects density and specific heat changes. Water often uses 500, while glycol blends require reduced values.
How to Use This Calculator
- Choose heating or cooling mode to match the loop application.
- Enter the system load and expected temperature difference.
- Select the fluid type or enter a custom constant.
- Provide internal pipe diameter, target velocity, and piping resistance values.
- Click the calculate button to display flow, head, pressure drop, and velocity checks.
- Use CSV or PDF export for reporting, design reviews, or client records.
Frequently Asked Questions
1. What does a hydronic flow calculator estimate?
It estimates required loop flow from thermal load and temperature difference. It also checks velocity, friction head, and pressure drop for piping and pump selection.
2. Why is the fluid constant important?
The constant captures fluid heat capacity and density effects. Water commonly uses 500, while glycol mixtures use lower values because they transport less heat per gallon.
3. Can I use this for chilled water systems?
Yes. Select cooling mode and enter the proper load and temperature difference. You should also use the correct fluid constant for any glycol blend.
4. What is a good hydronic pipe velocity?
Many designs target about 2 to 8 feet per second, depending on pipe size, noise limits, erosion risk, and energy efficiency goals.
5. Why compare design flow with velocity target flow?
That comparison shows whether the chosen pipe diameter suits the required duty. Large gaps can indicate excessive velocity, undersized piping, or overconservative assumptions.
6. Does total head equal pump head exactly?
No. Pump selection usually includes valves, coils, fittings, strainers, and safety margin. This calculator gives a practical estimate, not a full manufacturer selection curve.
7. Should I use supply and return temperatures?
Yes, when known. They help validate the temperature spread and confirm your ΔT assumptions reflect actual heating or cooling loop conditions.
8. When should I use a custom fluid factor?
Use a custom value when manufacturer data gives a specific heat-transfer constant for your exact fluid blend, temperature range, or specialty process solution.