Geothermal equipment
Geothermal Equipment Selection: Water-to-Air, Water-to-Water, Radiant, and Hot Water
Direct answer: geothermal equipment selection starts with the load and the delivery system. Water-to-air equipment serves ducted air systems. Water-to-water equipment serves hydronic loads such as radiant floors or water coils. Domestic hot water functions are model-specific. The loop must still support the equipment’s EWT, GPM, pressure drop, antifreeze, and control requirements.
The right question is not “which geothermal unit is best?” The better question is “what loads must this machine serve, what temperatures does each load need, and can the loop and pumps support those conditions?”
Definitions
Water-to-Air
A geothermal heat pump that transfers heat between loop water and a forced-air duct system.
Water-to-Water
A geothermal heat pump that transfers heat between loop water and a hydronic water circuit.
Radiant Load
A hydronic heating load, often floors or panels, with water-temperature needs that must match the equipment and controls.
Domestic Hot Water Function
A model-specific hot-water assist or production arrangement that must follow the manufacturer literature and plumbing requirements.
Selection Inputs
| Input | Why it matters | Question to ask |
|---|---|---|
| Load calculation | Equipment capacity should be selected from the building load, not only old tonnage. | What heating and cooling loads are being served? |
| Delivery system | Ducted air, radiant floors, fan coils, and water heating need different equipment and controls. | Is the load air-side, water-side, or mixed? |
| Temperature requirements | Radiant and water-heating applications may need different leaving-water temperatures than ducted air systems. | What supply temperatures are required at design conditions? |
| Loop EWT and flow | Capacity and efficiency ratings depend on entering water temperature and flow. | Can the loop deliver the design EWT and GPM? |
| Pressure drop | Water-to-water and multi-load systems can add pumps, valves, tanks, and heat exchangers. | Has pump head been checked for every operating mode? |
| Controls | Multi-load systems need control logic that prevents loads from fighting each other. | How are priority, staging, and lockouts handled? |
Equipment choice also decides what the room has to hold. The geothermal mechanical room checklist is where I check clearance, condensate, and electrical before I commit to a configuration.
Decision Logic
- Start with Manual J or other accepted load output for the building.
- Separate ducted air loads, hydronic loads, and domestic hot water functions.
- Select equipment using manufacturer performance data at the expected EWT and GPM.
- Check whether the loop, flow center, and pumps support each operating mode.
- Confirm electrical, condensate, duct, hydronic, tank, and control requirements.
- Document what the selected equipment is and is not intended to serve.
Worked Example
Example only: a home has ducted cooling, radiant slab heating in one area, and a domestic hot water goal. A single water-to-air selection may serve the ducted load but not the radiant load. A water-to-water or mixed-equipment design may be needed, and the final answer depends on loads, required water temperatures, controls, tanks, and manufacturer limits.
Field Checklist
- Heating load, cooling load, and any hydronic load are listed separately.
- Equipment type is identified as water-to-air, water-to-water, or mixed.
- Manufacturer data is checked at design EWT and GPM.
- Loop pressure drop, heat-pump pressure drop, and pump head are documented.
- Controls, staging, backup heat, condensate, ductwork, tanks, valves, and service clearances are reviewed.
- Domestic hot water functions are verified against the exact manufacturer literature for the selected model.
Safety And Professional Boundary
Equipment selection affects electrical service, refrigerant circuit service, hydronic pressure, antifreeze, water heating, condensate, controls, and code compliance. Do not select or pipe geothermal equipment from category names alone.
When To Call Hartzell’s
I am IGSHPA accredited and a ClimateMaster GeoElite dealer, so equipment selection here is done against manufacturer performance data for the model being considered, not against a rule of thumb. Call 405-375-4822 and I will run the loads before anybody picks a box.
Call Hartzell’s when a project has mixed ducted, radiant, or hot-water goals and you need the equipment, loop, pump, and controls reviewed together before a model is selected.
Related geothermal pages
Primary sources used
These sources set the technical context. The page does not replace the model-specific manual, local code, or field measurements for a real job.
- ENERGY STAR geothermal heat pump key product criteria – Water-to-air, water-to-water, and direct geoexchange product category definitions plus COP/EER rating context.
- ACCA Manual J residential load calculation – Residential load calculation boundary before geothermal equipment or loop selection.
- ACCA Manual S residential equipment selection – Residential equipment selection from load calculation and manufacturer performance data.
- ClimateMaster Tranquility 30 Digital TE installation manual – Model-specific startup, P/T port flow checks, water-side pressure drop, fluid, antifreeze, and servicing boundary examples.
FAQ
What is the difference between water-to-air and water-to-water geothermal?
Water-to-air equipment heats or cools air for duct systems. Water-to-water equipment heats or chills water for hydronic uses such as radiant floors or fan coils, depending on the system design.
Can geothermal make domestic hot water?
Some systems can support domestic hot water functions through model-specific options, but the plumbing, controls, tank arrangement, and operating limits must match the manufacturer literature.
Should equipment be chosen before the loop?
Equipment and loop design have to be coordinated because EWT, GPM, pressure drop, capacity, and controls affect each other.