A geothermal system is a heat pump that uses the ground instead of the outdoor air. It heats and cools your home, and in many setups it helps with hot water too. It doesn't burn fuel in the house. It runs on electricity and moves heat that is already in the ground.
How a ground-source heat pump works
A few feet below the surface, the ground stays at a fairly steady temperature all year. In the Ohio Valley that is somewhere in the 50s Fahrenheit, whether it's a humid July afternoon or a January cold snap. A geothermal system circulates water, usually mixed with antifreeze, through a loop of buried pipe. In winter the fluid picks up heat from the ground and carries it to the heat pump inside the house. In summer the process reverses, and the system pulls heat out of your home and sends it into the ground.
Inside, the heat pump works like any other: a compressor, refrigerant and coils move heat from one place to another. The difference is what it trades heat with. An air-source heat pump has to pull heat from outdoor air that might be in the single digits on the coldest nights. A geothermal unit pulls from a loop that stays much warmer than that all winter, and in summer it rejects heat into ground that is much cooler than the outdoor air. That steady source is why ground-source systems are among the most efficient ways to heat and cool a home.
Loop types
The buried loop is high-density polyethylene pipe with heat-fused joints. How it goes in the ground depends on your property:
- Horizontal loops are laid in trenches several feet deep. They need the most yard space and are often used on larger lots or in new construction, where the ground is already being dug.
- Vertical loops go into drilled boreholes, often a few hundred feet deep. They take up little surface area, which makes them the usual choice on smaller lots or where rock and slopes rule out trenching.
- Pond loops are coils of pipe sunk in a pond or lake on the property. The water has to be deep enough and large enough year-round for this to work.
Once installed, the loop is out of sight and has no moving parts. It is built to last for decades. When the indoor heat pump eventually wears out, the loop usually stays in place and gets connected to the new unit.
The benefits and the tradeoffs
On the plus side: high efficiency in both heating and cooling. No outdoor condenser making noise or collecting cottonwood and leaves. No gas burning inside the house, so no flue and no combustion heat exchanger. Many units can also send some waste heat to your water heater through a device called a desuperheater.
On the other side: installation costs more than a conventional furnace and air conditioner, mostly because of the drilling or trenching. The yard gets torn up during loop work. The design has to be right. The loop must be sized to the home's heating and cooling load, which starts with a Manual J load calculation, and an undersized loop struggles through a long cold stretch. Ductwork matters as much as it does with any system, because a geothermal heat pump is only as good as the air it can move through the house.
Is geothermal a fit for your home?
It tends to make the most sense when you're building new, replacing both heating and cooling at the same time, don't have natural gas available, have room on the lot for a loop, and plan to stay in the house a long time. It's a harder case when your current equipment still has years left, or when the property has no practical place for a loop.
If you're weighing a geothermal system, call JM Mechanical at (513) 667-8484 or request service online. We'll talk through your property, your ductwork and what a load calculation shows before anyone talks about equipment.