To design a geothermal heating system, assess your location’s geothermal potential, select appropriate heat pumps, size the system based on your heating needs, and install a ground loop or well system to efficiently transfer heat from the earth to your home.
Geothermal heating systems harness the earth’s stable underground temperatures to provide energy-efficient climate control. Unlike traditional HVAC systems, geothermal designs require careful planning of ground loops, heat pumps, and distribution systems tailored to your property’s unique characteristics.
Step 1: Conduct a Detailed Site Survey
Before designing your system, assess these critical site factors:
- Soil composition – Clay transfers heat better than sand
- Groundwater availability – Determines open vs closed loop options
- Land area – Horizontal loops need more space than vertical
- Existing infrastructure – Ductwork compatibility with new system
For example, a property with limited yard space but access to groundwater might use a standing column well system instead of horizontal trenches.
Step 2: Calculate Heating Load Requirements
ACCA Manual J Calculations
The industry standard for residential buildings requires:
| Climate Zone | BTU/sq ft/hour |
|---|---|
| Northern (Maine, Minnesota) | 20-25 |
| Central (Ohio, Missouri) | 15-20 |
| Southern (Texas, Florida) | 10-15 |
For a 2,000 sq ft home in Chicago (20 BTU/sq ft):
2,000 x 20 = 40,000 BTU/hour requirement
Step 3: Select and Size the Heat Pump
Key specifications to match:
- Capacity: 40,000 BTU = ~3.3 ton unit (12,000 BTU/ton)
- Efficiency: Look for COP ≥ 4.0 (4 units heat per 1 unit electricity)
- Flow rate: 3 GPM per ton → 10 GPM for 3.3 ton
Consider hybrid systems that combine geothermal with supplemental heating for extreme cold snaps.
Step 4: Design the Ground Loop System
Closed Loop Options
Vertical (Borehole)
- 150-200 ft depth per ton
- 3.3 ton system = 500-660 ft total
- Uses HDPE pipes with thermally-enhanced grout
Horizontal
- Requires 400-600 ft of trench per ton
- Needs 0.25-0.5 acres of clear land
- Slinky coil configurations save space
The U.S. Department of Energy provides detailed soil conductivity data by region to refine loop sizing.
Step 5: Plan the Distribution System
Match existing infrastructure or design new:
- Forced air: 400 CFM per ton → 1,320 CFM total
- Hydronic: Use with baseboard heaters or radiant floors
- Dual-fuel: Combine with existing furnace for backup
Advanced Design Considerations
- Thermal banking: Store summer heat for winter use
- Direct exchange: Refrigerant in ground loops (no heat exchanger)
- Hybrid systems: Combine with solar thermal for higher efficiency
According to IGSHPA standards, proper design can achieve 400-600% efficiency compared to 90-98% for gas furnaces.
