Special Section

Energy From the Earth

a newly popular way to keep the lights on can also keep our plants growing

Eric Christenson, photos by Andrea Paulseth |

Geothermal is exactly what it sounds like: heating using the ground. And it’s becoming pretty trendy for new homes to utilize geothermal technology as a sustainable, green way to heat their homes and save on energy bills.

But what you don’t typically see is what’s happening at Down to Earth Garden Center’s Eau Claire location: The greenhouse at Down to Earth isn’t that huge, but it’s a completely sustainable environment that take advantage of geothermal.

They installed geothermal in 2010 in partnership with their neighbors Water Source, a water and heating company that specializes in geothermal.

Ben Polzin, Down to Earth’s VP of retail operations said their system works in tandem with a little added insulation in the lower level and open ventilation on every side of the greenhouse to make for a completely sustainable way to grow plants efficiently with low energy costs. Whereas in a typical greenhouse, heaters are in the air heating downward, trapping a lot of rising heat near the top of the building, geothermal effectively heats from the ground up.

“Heat rises, so if you’re starting half way up already, only x-amount of that heat is getting down where it’s usable,” Polzin said. “It’s heating as it goes up.”

Basically the way geothermal works is it’s a self-contained unit deep underground that water gets pumped through.It goes through several loops underground until it warms up to about 55 degrees, then gets pumped back into the unit, which then uses friction to heat it up further, and pushes it out under the floor of the greenhouse which radiates up through the greenhouse.

But really, it’s the combination that makes the difference.

Most greenhouse walls have two-layer polycarbonate walls, but Down to Earth’s has a third squished in there for the bottom three feet or so, which allows the heat from the ground to stabilize a bit before going up.

Then instead of using fans, the greenhouse has giant ventilation doors on each side of the building, which allows natural breeze to come through.

“The ventilation is the big thing,” Polzin said. “There’s none of those big, huge, electricity-sucking fans, and the exhaust shutters — it’s all-natural. It’s quieter for the customers and yet we still get good airflow.”

Without hard-and-fast insulation in the greenhouse, it makes sense to get your heat in the most efficient way possible so that you’re not sucking down energy to just release the heat into the air.

And it actually keeps the plants pretty dry too, which is usually pretty essential. Sure, they have to modify the way they water, but it means that plants aren’t sitting in water all day, which isn’t great either.

If there’s a drawback to geothermal, it’s the involved installation process. Basically, it’s costly — you have install an additional backup heater and tear up the ground — but Polzin said it’s worth it for how they use it. They luck out in the fact that’s not a huge greenhouse.

They seem to be on the upswing of a trend, if not setting one themselves.
“House-wise, I definitely see it as a trend,” he said. “A lot more people are putting it in their houses. It’s a very efficient way to heat a house. Greenhouse-wise, it’s not catching on yet.”