Why geothermal heat pumps are so much more efficient

HostWe spend so much of our lives trying to keep our homes at just the right temperature. Usually, that means burning something, like gas or wood, to create heat when it's cold out. But there's a way to heat a house that feels almost like a cheat code because it uses the dirt in your own backyard. Why is tapping into the ground so much more effective than just using a normal furnace?

GuestWell, it helps to change how we think about heat. When you use a furnace or a space heater, you're making heat. You take a fuel, you set it on fire, and you turn that energy into warmth. But a heat pump doesn't make anything. It's more like a delivery truck. Its only job is to pick up heat from one place and drop it off in another. The reason the ground version is so good at this is that the earth is a great place to store energy. If you dig down just six or eight feet, the temperature of the dirt stays pretty much the same all year round. It doesn't matter if there's a blizzard or a heat wave up top. Down there, it's always around fifty or fifty five degrees.

HostI get that the ground stays steady, but fifty degrees still sounds pretty cold if you're trying to keep a house warm. If the ground is that chilly, how does it actually help me when I want my living room to be seventy?

GuestThat's where the clever part of the pump comes in. Inside the pipes that go into the ground, there's a special fluid. This liquid is much colder than the dirt around it, so even though fifty degrees feels cold to us, to that fluid, the ground is actually warm. As the fluid travels through the pipes, it soaks up that heat from the earth. Then, the pump brings it back into the house and squeezes it. When you squeeze a gas or a liquid very tightly, it gets much hotter. Think about how a bike pump feels warm after you use it for a minute. By the time that fluid is done being squeezed, it's hot enough to warm up the air blowing through your vents. It's efficient because you're only using electricity to run the pump and the squeezer, not to actually create the heat itself. You're just stealing it from the yard.

HostBut we already have heat pumps that sit outside the house and pull heat from the air. Those are much easier to put in because you don't have to dig up the whole lawn. Why would I bother with all that digging if the air is right there?

GuestAir is easy to get to, sure, but it's a terrible partner when the weather gets extreme. Think about a really cold winter night. If it's ten degrees outside, there's not much heat in the air for a pump to grab. It has to work incredibly hard to find any warmth at all, and eventually, it just gives up and switches over to a backup heater that uses a lot of power. But the ground doesn't care about the winter. The dirt is still sitting there at fifty degrees. The pump in the ground has the same easy job in January that it has in October. It doesn't have to struggle because its source of heat never goes away. That's why it uses so much less power over the course of a year. It never has to fight against the weather.

HostIt still sounds like a massive project, though. I mean, you're talking about burying hundreds of feet of pipe. Is it really worth the mess and the cost of bringing in a backhoe just to save some money on the electric bill?

GuestIt's a big lift at the start, no doubt. You're basically building a piece of equipment that will last for fifty years or more. But the math is hard to ignore. For every one unit of electricity you use to run the pump, you get about four units of heat out of it. A high end gas furnace might get you close to one for one, but it can never go over that because it's limited by how much energy is in the fuel. The ground loop is essentially giving you three units of heat for free for every one you pay for. And the best part is that it works in reverse during the summer. Instead of looking for heat in the ground, the pump takes the extra heat from your hot house and dumps it back into the cool earth. It's like having a giant sponge that can either give you heat or take it away, depending on what you need.

HostSo it's not just a heater, it's a way to use the earth like a massive thermal bank account that you can deposit heat into or withdraw it from.

GuestExactly, and because the ground is so dense, it can hold onto that energy way better than the thin air can. The dirt under your lawn is the most reliable battery you'll ever own.

HostThe soil in the backyard turns out to be a lot more than just a place for the grass to grow.