Formula Used
Load conversion: Btu/h = kW × 3412.142, or tons × 12000.
Heating ground load: Ground load = Building load − Building load / COP.
Cooling ground load: Ground load = Building load + Building load / COP.
Adjusted capacity: Rate = Base rate × Soil factor × Fluid factor.
Total pipe length: Length = Ground load / Rate × Safety factor.
Flow: Total flow = Tons × selected gpm per ton.
Velocity: Velocity = Circuit flow / pipe area.
Pump power: HP = gpm × head × specific gravity / (3960 × pump efficiency).
How to Use This Calculator
Enter the design heating or cooling load first. Select the correct load unit. Choose the loop style that matches the planned field. Add the expected COP, soil conductivity, fluid data, pipe size, and circuit count. Use a custom capacity rate when a soil test or design manual gives a better value.
Press Calculate to view loop length, flow, pressure loss, pump head, and pump power. Use CSV for spreadsheet work. Use PDF for a simple report. Final geothermal design should be checked by a qualified designer before installation.
Example Data Table
| Case |
Loop Type |
Load |
COP |
Soil K |
Circuits |
Flow Rate |
| Small home |
Vertical bore |
36,000 Btu/h |
4.0 |
1.2 |
4 |
3 gpm per ton |
| Long trench |
Horizontal trench |
48,000 Btu/h |
3.8 |
1.0 |
6 |
3 gpm per ton |
| Compact yard |
Slinky coil |
30,000 Btu/h |
4.2 |
0.9 |
3 |
2.8 gpm per ton |
Geothermal Ground Loop Planning Guide
Why Ground Loop Size Matters
A geothermal ground loop moves heat between the building and the earth. Its size affects comfort, pump energy, and equipment life. A short loop can overwork the heat pump. A very long loop can raise installation cost. The goal is balanced design.
Heating And Cooling Loads
The calculator starts with the building load. This load may come from a Manual J report, an energy model, or measured equipment capacity. Heating and cooling use different ground exchange values. In heating, the compressor adds useful heat. So the ground provides less than the full building load. In cooling, compressor energy also becomes heat. So the ground must reject more than the indoor cooling load.
Soil And Fluid Effects
Soil conductivity changes loop length. Wet soil often transfers heat better. Dry sand usually needs more pipe. Antifreeze also matters. It protects the loop from freezing, but it can reduce heat transfer and increase pressure loss. The calculator applies simple factors for these effects. A thermal conductivity test gives better data for larger projects.
Loop Layout Choices
Vertical bores work well where land is limited. They need drilling and careful grouting. Horizontal trenches may cost less when space is available. Slinky coils fit more pipe into a shorter trench. Pond loops can perform well when a suitable body of water exists. Each layout needs correct spacing and local approval.
Flow And Pumping
Good flow keeps heat transfer stable. Low velocity may trap air. High velocity can waste pump energy. The calculator estimates total flow, flow per circuit, pipe velocity, pressure drop, head, and pump watts. These results help compare pipe sizes and circuit counts.
Use Results Carefully
This tool is for planning and comparison. It does not replace a full geothermal design. Final work should include accurate loads, soil data, pipe tables, antifreeze tables, local codes, and manufacturer limits. A trained designer should confirm bore depth, trench layout, headers, flushing needs, and electrical pump demand before construction begins.
FAQs
What is a geothermal ground loop?
It is buried or submerged piping that moves heat between the earth and a geothermal heat pump. The loop carries water or antifreeze solution.
How accurate is this calculator?
It gives planning estimates. Accuracy depends on load data, soil conductivity, pipe data, antifreeze, and field layout. Final design needs professional review.
What does COP mean?
COP means coefficient of performance. It compares useful heating or cooling output with electrical input. Higher COP usually means lower operating energy.
Why is cooling ground load higher?
In cooling mode, the ground receives indoor heat plus compressor heat. That makes rejected heat higher than the building cooling load.
Why does antifreeze affect the result?
Antifreeze protects against freezing. It can also reduce heat transfer and increase pumping resistance. The calculator applies a simple correction.
What pipe velocity is preferred?
Many designs aim for moderate velocity. Very low velocity may trap air. Very high velocity can raise pump energy and noise.
Can I use custom capacity per foot?
Yes. Enter a custom rate when you have reliable local design data, soil test values, or manufacturer guidance for your loop type.
Does this replace a licensed design?
No. It supports early planning only. A qualified geothermal designer should verify loads, pipe pressure loss, bore spacing, codes, and equipment limits.