Latest / Cool Talk with Hartzell's | Your HVAC Questions, Answered! / Why Geothermal Rules of Thumb Fail

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Why Geothermal Rules of Thumb Fail · Cool Talk with Hartzell's | Your HVAC Questions, Answered!

0:00
SPEAKER_00: Picture this.
0:00
SPEAKER_00: Uh you live in Hennessy, Oklahoma, and seven years ago, you made this major investment in your home.
0:08
SPEAKER_01: Right, a big one.
0:08
SPEAKER_00: Yeah.
0:09
SPEAKER_00: You installed a state-of-the-art geothermal heating and cooling system.
0:13
SPEAKER_00: And for the first two years, you were just absolutely thrilled.
0:16
SPEAKER_00: I mean, it works perfectly.
0:17
SPEAKER_01: Utility bills are probably practically nonexistent, right?
0:20
SPEAKER_00: Exactly.
0:21
SPEAKER_00: The house is incredibly comfortable, and you're feeling pretty smart about your decision.
0:26
SPEAKER_00: But then, and this is where it turns summer rolls around in year seven.
0:30
SPEAKER_01: Oh no.
0:31
SPEAKER_01: Yeah.
0:31
SPEAKER_00: It's late July, the sun is just beating down, and suddenly the back of your house is baking.
0:36
SPEAKER_00: The system is running constantly, just fighting a completely losing battle against the heat.
0:41
SPEAKER_01: It's choking.
0:42
SPEAKER_00: It's completely choking.
0:43
SPEAKER_00: So you finally call a professional out to look at it and they deliver some devastating news.
0:48
SPEAKER_00: The original installer used a lazy regional rule of thumb instead of doing the actual map.
0:54
SPEAKER_01: Which happens way too often.
0:55
SPEAKER_00: They assumed you needed 600 linear feet of pipe per ton, hooked a four-ton load up to 2,400 feet of pipe, and completely ignored how the local clay soil in your yard physically behaves during a late summer drought.
1:09
SPEAKER_01: Aaron Powell They didn't account for the soil drying out.
1:11
SPEAKER_00: Right.
1:11
SPEAKER_00: And that single, totally preventable mathematical mistake is going to cost you$4,000 just to tear up your yard and add more pipe to get the system working the way it was supposed to in the first place.
1:22
SPEAKER_01: It is a painful scenario.
1:23
SPEAKER_01: And unfortunately, um it's far more common in the residential HVAC world than you might think.
1:29
SPEAKER_01: So welcome to today's deep dive.
1:31
SPEAKER_00: Yeah, let's unpad this.
1:32
SPEAKER_01: We are looking at a stack of incredibly detailed sources today to understand the invisible mechanics of geothermal energy.
1:39
SPEAKER_01: We have training materials from IGS HPA.
1:42
SPEAKER_00: That's the International Ground Source Heat Pump Association, right?
1:44
SPEAKER_01: Exactly, IGS HPA.
1:46
SPEAKER_01: We're also looking at data from Climate Master's GeoElite Design Software, geological and soil conductivity records from the USGS, and this is the really cool part the detailed field notes of Dave Hartzall.
1:58
SPEAKER_00: A master HVAC technician.
2:00
SPEAKER_01: Yes.
2:01
SPEAKER_01: With 45 years of experience out of Kingfisher, Oklahoma.
2:05
SPEAKER_01: So our mission today is to explore exactly why geothermal loop sizing is the single most critical and frankly the most frequently botched step in the entire installation process.
2:15
SPEAKER_00: Aaron Ross Powell Right.
2:16
SPEAKER_00: Because for anyone investing in home infrastructure, understanding that this invisible engine buried in your yard is, well, it's quite literally the difference between a system that runs flawlessly for 30 years and a five-year ticking time bomb.
2:29
SPEAKER_01: Aaron Powell That's a great way to put it.
2:30
SPEAKER_00: And while our sources use Central Oklahoma as a case study, you know, the thermodynamic principles we are going to explore apply whether you are installing a system in the American Midwest, the rocky terrain of New England, or just halfway across the world.
2:44
SPEAKER_01: The physics don't change.
2:45
SPEAKER_00: Right.
2:46
SPEAKER_00: So to understand why that specific system in Hennessy failed so spectacularly, we have to shift our focus away from the shiny hardware sitting in your mechanical room.
2:55
SPEAKER_00: We have to look at the dirt itself.
2:56
SPEAKER_01: Yeah, you really have to look at the ground as an active engine for moving heat.
3:00
SPEAKER_01: The soil is your heat exchanger.
3:02
SPEAKER_01: Every geothermal system relies on the ground to either absorb the heat your house generates in the summer or provide heat for your house in the winter.
3:11
SPEAKER_01: And uh the metric that governs how well that engine works is called soil thermal conductivity.
3:17
SPEAKER_00: Okay, so conductivity, what does it actually mean in plain English?
3:21
SPEAKER_01: In technical terms, it's a measure of how fast heat moves through the soil.
3:25
SPEAKER_01: We measure it in British thermal units or BTUs per hour per foot per degree Fahrenheit.
3:30
SPEAKER_01: Got it.
3:31
SPEAKER_01: So the higher that conductivity number is, the faster the heat transfers away from the buried pipe and into the surrounding earth.
3:38
SPEAKER_01: And higher conductivity basically means you need less prape overall to do the job.
3:42
SPEAKER_00: Okay, but how much does this conductivity actually vary from yard to yard?
3:46
SPEAKER_00: Are we talking about like microscopic differences or is it a massive swing depending on where you live?
3:51
SPEAKER_01: Aaron Powell Oh, the variations are massive.
3:53
SPEAKER_01: I mean, soil composition completely dictates the efficiency of the heat transfer.
3:56
SPEAKER_01: Dry sand, for example, is a terrible conductor.
3:59
SPEAKER_01: It sits at about 0.15 on that conductivity scale.
4:02
SPEAKER_00: Aaron Powell So it's basically an insulator.
4:04
SPEAKER_01: Almost, yeah.
4:05
SPEAKER_01: But wet clay is fantastic.
4:06
SPEAKER_01: That comes in at about 0.7.
4:08
SPEAKER_01: And if you are digging deep into solid bedrock, uh that ranges anywhere from 1.20 to 2.50.
4:15
SPEAKER_00: Wow, okay.
4:16
SPEAKER_00: And looking at the reality of central Oklahoma, which you know Dave Hartzall's field notes focus on, you're mostly dealing with red clay sitting over sandstone.
4:25
SPEAKER_01: Exactly.
4:25
SPEAKER_00: And the sources mention that the top four feet of that soil experience wild seasonal moisture swings depending on the weather.
4:32
SPEAKER_00: But below six feet, things get much more stable.
4:34
SPEAKER_00: The ground temperature locks in at roughly 62 degrees year-round.
4:38
SPEAKER_01: Right.
4:38
SPEAKER_01: Below six feet, you're clear of the surface, weather impacts.
4:41
SPEAKER_00: I mean, think of wet clay like a water slide for heat.
4:44
SPEAKER_00: The moisture in the soil lubricates the thermal transfer.
4:47
SPEAKER_00: The heat just zips right through it, moving away from the plastic pipe and into the earth with basically zero friction.
4:53
SPEAKER_01: I like that analogy.
4:54
SPEAKER_00: But dry clay is like uh it's like trying to slide down a dry plastic tube at a playground in shorts.
4:59
SPEAKER_00: The heat just gets stuck.
5:00
SPEAKER_00: That's nowhere to go.
5:01
SPEAKER_01: Yeah, that's exactly what's happening mathematically.
5:04
SPEAKER_00: But wait, I have a question here.
5:06
SPEAKER_00: If wet clay is such a great conductor at a 0.70 rating, why did that house in Hennessy fail?
5:12
SPEAKER_00: The soil there is notoriously heavy clay.
5:16
SPEAKER_01: Well, because we aren't just talking about clay, we are talking about the physical difference between wet clay and bone-dry clay.
5:22
SPEAKER_00: Oh, right.
5:22
SPEAKER_00: The drought.
5:23
SPEAKER_01: Exactly.
5:24
SPEAKER_01: At a microscopic level, water acts as a thermal bridge between the individual soil particles.
5:30
SPEAKER_01: When moisture is present, heat flows easily across those bridges.
5:33
SPEAKER_01: But late summer droughts, which are practically a guarantee in Oklahoma and a lot of other places, they dry out that clay deep down.
5:40
SPEAKER_00: So the water leaves?
5:41
SPEAKER_01: Right.
5:41
SPEAKER_01: The water evaporates, and those thermal bridges are replaced by microscopic pockets of air.
5:46
SPEAKER_01: And air is a terrible conductor.
5:48
SPEAKER_01: As we said, it's an insulator.
5:49
SPEAKER_01: When that happens, the thermal conductivity just plummets.
5:52
SPEAKER_00: So the soil physically transforms.
5:54
SPEAKER_01: Completely.
5:55
SPEAKER_01: According to the data, during a severe drought, that beautiful 0.77 conductivity drops to just 60% of its design expectation.
6:03
SPEAKER_01: It becomes closer to a 0.40 or even lower.
6:06
SPEAKER_00: Man, so the original installer for that Hennessy house, they designed a system that worked perfectly for like an average spring day.
6:14
SPEAKER_01: And the ground was damp and heat could easily flow, yeah.
6:16
SPEAKER_00: But they completely ignored the worst case scenario.
6:19
SPEAKER_00: Yeah.
6:19
SPEAKER_00: And because that soil moisture can plummet the conductivity by 60% during a drought, relying on regional averages or industry rules of thumb is just a recipe for disaster.
6:31
SPEAKER_01: It really is.
6:32
SPEAKER_00: Our sources expose this very specific, kind of lazy contractor method.
6:36
SPEAKER_01: Yeah.
6:37
SPEAKER_00: The 500 or 600 feet per ton rule.
6:39
SPEAKER_01: Which fundamentally misunderstands the physics of heat transfer in a dynamic environment.
6:44
SPEAKER_01: Uh inexperienced installers use these flat, standardized numbers, you know, just averaging them across entirely different soil types and climate zones.
6:51
SPEAKER_00: Just to make their quoting process faster, I assume.
6:53
SPEAKER_01: Exactly.
6:54
SPEAKER_01: It's a shortcut.
6:55
SPEAKER_01: But think about it.
6:56
SPEAKER_01: If you have good wet clay, the math might show you only need 400 feet of pipe per ton of heating and cooling capacity.
7:04
SPEAKER_01: But if you have dry, sandy soil on the exact same property, maybe just on the other side of the driveway where the drainage is different, after a severe drought, you might need 600 feet per ton to handle the exact same load.
7:16
SPEAKER_00: Right.
7:17
SPEAKER_00: So if an installer just uses a flat 500 feet rule everywhere, they are missing the worst case scenario by a massive margin.
7:25
SPEAKER_01: A system that fails on the worst week of the year is a failed system.
7:28
SPEAKER_01: I mean, what's fascinating here is you don't size a heating and cooling system for a mild Tuesday in the middle of spring when it's 72 degrees outside.
7:37
SPEAKER_00: No, you need it when it's unbearable out.
7:39
SPEAKER_01: Aaron Powell You size it for the absolute extreme.
7:41
SPEAKER_01: You size it for the bone-dry 105-degree late summer afternoon when your house is absorbing maximum solar radiation and your soil's thermal conductivity is at its absolute lowest.
7:52
SPEAKER_00: Okay, but if the math is this volatile and the stakes are this high, I mean, we are talking about thousands of dollars to dig up a yard and fix a mistake.
8:00
SPEAKER_00: Why are professionals still using these rules of sum?
8:02
SPEAKER_00: Is it just stubbornness or a fundamental misunderstanding of the physics?
8:07
SPEAKER_01: Aaron Powell It's heavily leaning toward a lack of specific thermodynamic training.
8:11
SPEAKER_01: Doing the actual site-specific math requires specialized software, geological data, and an understanding of thermodynamics that goes far beyond just, you know, standard air conditioner installation.
8:23
SPEAKER_01: Trevor Burrus, Jr.
8:23
SPEAKER_00: Right.
8:23
SPEAKER_00: It's not just swapping out a unit.
8:25
SPEAKER_01: Trevor Burrus, Jr.: No, not at all.
8:26
SPEAKER_01: A rule of thumb requires no calculation.
8:28
SPEAKER_01: You just multiply the size of the house by 500 and start digging.
8:31
SPEAKER_01: But as we see with the Hennessy example, skipping the math translates to an incredibly expensive crisis for the homeowner down the road.
8:38
SPEAKER_00: Aaron Powell What's really insidious about this too is that when installers do use those flawed rules of thumb and undersize the loop, the system doesn't immediately break.
8:47
SPEAKER_01: Nope, it works fine at first.
8:49
SPEAKER_00: Right.
8:50
SPEAKER_00: The homeowner has no idea there's a problem on day one.
8:53
SPEAKER_00: Instead, it triggers a hidden creeping failure over a span of years, which makes it incredibly difficult for people to spot until it is way too late.
9:02
SPEAKER_01: Aaron Powell Yeah.
9:02
SPEAKER_01: The technical term for this creeping failure is thermal saturation.
9:06
SPEAKER_01: And understanding how thermal saturation physically changes the ground is it's crucial.
9:12
SPEAKER_00: So what's actually happening underground?
9:14
SPEAKER_01: Well, an undersized loop will actually work fine for the first two to five years.
9:17
SPEAKER_01: When you first bury that pipe, the massive volume of soil around it is sitting at its natural design temperature.
9:23
SPEAKER_01: Let's say that nice stable 62 degrees we mentioned.
9:27
SPEAKER_01: Okay.
9:27
SPEAKER_01: Makes sense.
9:28
SPEAKER_01: Heat moves from high to low, so a 90-degree fluid coming from your house easily dumps its heat into that 62 degree dirt.
9:36
SPEAKER_00: But then comes the drift.
9:38
SPEAKER_01: Gradually, year after year, the system rejects more heat into the ground in the summer than the undersized patch of soil can naturally dissipate.
9:46
SPEAKER_01: Oh, okay.
9:47
SPEAKER_01: And in the winter, it extracts more heat than the soil can resupply because the volume of dirt just isn't large enough to breathe and naturally reset its temperature during the shoulder seasons of spring and fall.
9:58
SPEAKER_01: So the physical temperature of the earth surrounding your pipes permanently changes.
10:02
SPEAKER_00: I mean it's like a tiny hidden overdraft fee on your thermal bank account.
10:07
SPEAKER_00: You know, you're overdrawing your soil's capacity just a little bit every single year, the degree here, a degree there.
10:12
SPEAKER_00: You don't realize you are bankrupt until five years later when the massive bill comes due.
10:17
SPEAKER_01: That's spot on.
10:18
SPEAKER_01: And if we connect this to the bigger picture, over five to ten years, that drift grows into a canyon.
10:25
SPEAKER_01: The entering water temperature, which is the temperature of the fluid returning from the ground loop back into your heat pump inside the house, it just gets way too hot in the summer.
10:35
SPEAKER_00: Right, because the ground is saturated.
10:37
SPEAKER_01: Exactly.
10:38
SPEAKER_01: So instead of the fluid returning at a cool 70 degrees, it comes back at 95 degrees.
10:44
SPEAKER_01: The heat pump has nowhere to dump the heat from your living room.
10:47
SPEAKER_00: And what happens to the equipment?
10:48
SPEAKER_01: The compressor has to work twice as hard, drawing massive amounts of electricity, and eventually the system just completely locks out on a high pressure safety switch to prevent the equipment from melting down.
11:00
SPEAKER_00: Wow.
11:00
SPEAKER_00: And this slow failure mode explains exactly why so many homeowners are blindsided.
11:05
SPEAKER_00: They wake up one July, the house is hot, the system is running nonstop, and their electric bill has skyrocketed.
11:11
SPEAKER_01: They think it's a broken part.
11:13
SPEAKER_00: Yeah, they assume a fan motor broke or a compressor died or they just need a quick$200 repair.
11:19
SPEAKER_00: But the technician arrives and tells them the mechanical equipment is actually fine.
11:23
SPEAKER_00: The ground itself is thermally saturated.
11:26
SPEAKER_00: It is a multi-year mathematical failure that has finally caught up to them.
11:30
SPEAKER_01: Right.
11:30
SPEAKER_01: And to prevent this slow thermal bankruptcy, modern professionals replace that lazy guesswork with exact math.
11:37
SPEAKER_01: Thank goodness.
11:38
SPEAKER_01: They rely on software, specifically programs like the IGSHPA ground loop design software.
11:45
SPEAKER_01: A properly trained, accredited installer uses this to simulate the exact thermodynamic lifespan of your specific yard.
11:53
SPEAKER_00: And the number of variables this software factors in is incredible.
11:56
SPEAKER_00: It doesn't just do static multiplication, it runs a simulation of how the ground will react over thousands of cycles.
12:02
SPEAKER_01: It really gets into the weeds.
12:03
SPEAKER_00: It calculates the specific heat load of the house, the deep ground temperature, the exact pipe configuration you're using, the specific antifreeze mixture in the lines, and the target entering water temperatures.
12:14
SPEAKER_00: All of it.
12:14
SPEAKER_00: It takes all of that and models the heat pulses over 360 months or 30 years, ensuring the ground has enough volume to breathe and reset every single winter.
12:24
SPEAKER_01: Exactly.
12:24
SPEAKER_01: And it outputs the exact minimum loop length required to meet your extreme weather conditions without risking thermal saturation.
12:31
SPEAKER_01: And the output is the loop you must install.
12:34
SPEAKER_00: No exceptions.
12:35
SPEAKER_01: As Dave Hartzell's field training materials point out, you do not install 10% less to save money on trenching, and you do not install 10% more just to be safe.
12:45
SPEAKER_01: The calculated number is the number.
12:47
SPEAKER_00: Okay, let's look at a concrete example from the sources to see how this plays out in the real world.
12:51
SPEAKER_00: Let's take a standard three-ton load.
12:53
SPEAKER_00: So that's about 36,000 BTUs of heating and 42,000 BTUs of cooling.
12:58
SPEAKER_01: Okay, pretty typical.
12:59
SPEAKER_00: In average Kingfisher clay, using a horizontal loop configuration where trenches are dug six feet deep across a wide yard, the software dictates you need exactly twelve hundred to fourteen hundred linear feet of pipe.
13:11
SPEAKER_01: Which is about four hundred to four hundred and seventy feet per ton.
13:14
SPEAKER_00: Right.
13:15
SPEAKER_00: But if that exact same house was sitting on a drier site with sandy soil, that requirement jumps to 1,500 to 1800 feet.
13:23
SPEAKER_00: The software adjusts for the soil's microscopic mechanics.
13:27
SPEAKER_00: The rule of thumb does not.
13:29
SPEAKER_01: And we can also look at that same three-ton load using a vertical loop configuration.
13:34
SPEAKER_01: Instead of digging massive trenches across an acre of land, a drilling rig bores straight down.
13:40
SPEAKER_00: Oh, right, deep into the earth.
13:42
SPEAKER_01: Yeah, and with the deep ground sitting at a highly stable temperature and tapping directly into the intense conductivity of the bedrock, the software tells us this home only needs four boreholes, each 230 feet deep.
13:54
SPEAKER_01: That is 920 total feet of bore.
13:57
SPEAKER_00: Right, because vertical loops use significantly less total pipe because the deep ground is entirely isolated from surface weather.
14:03
SPEAKER_01: Right.
14:03
SPEAKER_00: And they fill those boreholes with a specialized grout that provides perfect, unbroken thermal contact between the plastic pipe and the rock.
14:10
SPEAKER_01: Yeah.
14:10
SPEAKER_00: It takes up a fraction of the land space, even though it costs more up front because, well, massive drilling rigs are expensive to operate.
14:16
SPEAKER_01: They are.
14:17
SPEAKER_01: But there's a flip side to this mathematical precision.
14:20
SPEAKER_01: We have talked a lot about the dangers of undersizing your loop and cooking your house in the summer.
14:25
SPEAKER_01: But the sources highlight the exact opposite problem, which is rampant in the industry.
14:30
SPEAKER_00: Oversizing.
14:31
SPEAKER_01: Yes, oversizing.
14:32
SPEAKER_01: Some contractors know the rule of thumb is risky, so to avoid doing the actual thermodynamic calculations, they just blindly add 20 to 30% extra pipe to whatever their guess was.
14:43
SPEAKER_00: Right.
14:43
SPEAKER_00: Here's where it gets really interesting.
14:45
SPEAKER_00: They think they're playing it safe, but that is not cheap.
14:48
SPEAKER_00: Not at all.
14:49
SPEAKER_00: On a horizontal install, adding that extra 20 to 30% means 250 to 400 extra feet of trenching, extra pipe, and extra labor.
14:58
SPEAKER_00: That easily adds$2,000 to$4,000 to the install cost.
15:01
SPEAKER_01: It adds up fast.
15:02
SPEAKER_00: And if it's a vertical install, playing it safe means drilling an entire extra 200-foot borehole, which tax on$3,000 to$5,000 extra.
15:10
SPEAKER_01: And the thing is, an oversized loop will not hurt the system mechanically.
15:14
SPEAKER_01: Your heat pump will run perfectly fine with extra pipe in the ground, but it forces the homeowner to pay thousands of dollars for thermal capacity they will literally never use.
15:23
SPEAKER_00: That's infuriating.
15:24
SPEAKER_01: It is essentially a financial penalty.
15:26
SPEAKER_01: A tax you are paying out of pocket to cover your installer's refusal to run a simple software simulation.
15:32
SPEAKER_00: So what does this all mean for you, the person actually writing the check?
15:37
SPEAKER_00: Now that you know the exact math exists and you know the hidden dangers of both undersizing and oversizing, how do you evaluate the contractor standing in your living room?
15:47
SPEAKER_01: How do you protect your investment?
15:48
SPEAKER_00: Exactly.
15:49
SPEAKER_01: Well, it comes down to demanding data.
15:51
SPEAKER_01: The absolute gold standard for finding your soil's conductivity is a physical field test called a thermal conductivity test, or TCT.
16:00
SPEAKER_00: Which is an incredibly intense physical process.
16:03
SPEAKER_00: To run a TCT, a crew actually drills a test borehole on your property and installs a temporary loop.
16:09
SPEAKER_01: Yeah, it's quite the operation.
16:11
SPEAKER_00: Then they hook up a specialized rig that uses an electric heating element to pump a precise known amount of heat into that loop for 48 solid hours.
16:20
SPEAKER_00: Sensors measure exactly how fast that heat dissipates into the surrounding Earth, graphing out a perfect dissipation curve.
16:26
SPEAKER_01: It gives you the undeniable real-world conductivity number for your specific site.
16:31
SPEAKER_00: It does, but a formal TCT costs between$3,000 and$5,000 just to run the test.
16:36
SPEAKER_01: Right.
16:36
SPEAKER_01: It's expensive.
16:38
SPEAKER_01: It is absolutely necessary for large commercial geothermal projects or massive residential jobs over six tons, where a sizing mistake could cost tens of thousands of dollars.
16:49
SPEAKER_00: Sure, that makes sense.
16:50
SPEAKER_01: But for a standard residential install, running a$5,000 test on a$20,000 system just doesn't make economic sense.
16:57
SPEAKER_01: For normal residential jobs, relying on the IGS HPA software, combined with regional USGS soil data and a mathematical adjustment for extreme drought conditions is highly accurate.
17:09
SPEAKER_00: But you have to verify they are actually using that software.
17:12
SPEAKER_00: Our sources provide a literal interrogation script for your quote.
17:15
SPEAKER_00: You need to ask the contractor, what is the loop length in feet?
17:19
SPEAKER_00: What specific software did you use to calculate it?
17:21
SPEAKER_00: What was your exact soil conductivity assumption?
17:23
SPEAKER_01: And did you adjust that conductivity number for extreme drought moisture conditions?
17:28
SPEAKER_00: Yes, all of that.
17:28
SPEAKER_01: You also need to verify the hardware specifications they are quoting.
17:32
SPEAKER_01: Like, are they using 34-inch SDR11 HDPE pipe?
17:36
SPEAKER_00: Okay, let's define that really quickly.
17:37
SPEAKER_00: HDPE is high density polyethylene, which is the incredibly durable plastic used for the underground loops.
17:44
SPEAKER_00: And SDR11 stands for standard dimension ratio 11.
17:48
SPEAKER_00: Right.
17:48
SPEAKER_00: It means the outside diameter of the pipe is exactly 11 times its wall thickness.
17:54
SPEAKER_00: That specific ratio is the industry sweet spot.
17:57
SPEAKER_00: It provides enough structural strength to handle the fluid pressure without bursting, but the walls are thin enough to allow for rapid heat transfer into the soil.
18:05
SPEAKER_01: Exactly.
18:06
SPEAKER_01: And if the quote is for a vertical system, you must ask how many boreholes they are drilling and what the exact depth of each hole is.
18:14
SPEAKER_01: You should also be looking at their industry credentials.
18:16
SPEAKER_00: What kind of credentials?
18:17
SPEAKER_01: Well, the source material highlights Dave Hartzell's operation as a benchmark for what a proper residential quote should look like.
18:23
SPEAKER_01: An installer should have decades in the trade, a master mechanical license and Nate certification.
18:28
SPEAKER_00: Okay, and NATE stands for North American Technician Excellence.
18:32
SPEAKER_00: It is essentially the rigorous board certification for HVAC technicians, proving they actually understand the physics of what they are installing, not just how to turn a wrench.
18:42
SPEAKER_01: Exactly.
18:42
SPEAKER_01: And they should carry IGS HPA accreditation.
18:45
SPEAKER_01: But the crucial detail you should look for in a contractor's process, which Hertzell uses as a standard, is documentation.
18:52
SPEAKER_00: What kind of documentation?
18:54
SPEAKER_01: Every single geothermal quote issued should include a printed, site-specific ground loop design software run.
19:02
SPEAKER_01: The soil conductivity assumption should be clearly printed right there on the estimate for you to see.
19:08
SPEAKER_00: A proper contractor will also factor in long-term maintenance, things like loop repressurization.
19:13
SPEAKER_01: That's a big one.
19:14
SPEAKER_00: Yeah, because during the first year of operation, those plastic HDPE pipes physically stretch and expand slightly under the pressure of the fluid.
19:23
SPEAKER_00: When the pipe expands, the internal pressure drops, which can reduce the flow rate and hurt the heat transfer.
19:28
SPEAKER_01: Right, it drops the efficiency.
19:30
SPEAKER_00: So a good maintenance plan includes coming back to top up the fluid and repressurize the loop to keep the flow optimal.
19:36
SPEAKER_00: But I have to push back here on behalf of the listener.
19:38
SPEAKER_01: Okay, go ahead.
19:39
SPEAKER_00: Look, is it really on you, the homeowner, to cross-examine a 30-year HVAC veteran about their soil conductivity assumptions and SDR 11 wall thickness?
19:51
SPEAKER_00: That feels incredibly intimidating.
19:53
SPEAKER_01: Yes, it is completely on you.
19:55
SPEAKER_01: Because the right loop is the calculated loop, and you are the one who will be living with the consequences in year seven.
20:00
SPEAKER_01: Fair point.
20:01
SPEAKER_01: If you ask a contractor what soil conductivity they assumed, and they brush off the question with a smile and say, Oh, don't worry about it.
20:07
SPEAKER_01: We just use 500 feet per ton in this area, that is your cue to walk away.
20:12
SPEAKER_01: Do not let them roll the dice with your money.
20:14
SPEAKER_00: It's just not worth the risk.
20:16
SPEAKER_00: So to wrap this all up, geothermal loop sizing cannot be a guessing game.
20:21
SPEAKER_00: It must be a site-specific calculation based on the physical mechanics of thermal conductivity, not a lazy regional rule of thumb.
20:28
SPEAKER_01: Absolutely.
20:29
SPEAKER_00: It is absolutely vital that your system is designed for the worst case scenario.
20:32
SPEAKER_00: The bone-dry late summer drought when your soil turns into an insulator, not the gentle average of a spring day.
20:38
SPEAKER_01: Because an undersized loop condemns you to a slow, creeping, and very expensive five to ten year thermal death.
20:45
SPEAKER_00: And an oversized loop just picks your pocket up front for thousands of dollars in extra drilling and pipe you didn't need.
20:52
SPEAKER_01: The thermodynamics are non-negotiable.
20:55
SPEAKER_01: Whether you are dealing with a massive swing in conductivity in central Oklahoma red clay or navigating the dense bedrock of another continent entirely, the physical principles remain identical.
21:07
SPEAKER_00: Right.
21:07
SPEAKER_00: So whether you're building a new home or retrofitting an old one, applying this level of critical thinking to the experts you hire protects your biggest investment, your home.
21:17
SPEAKER_00: Don't settle for rules of thumb.
21:19
SPEAKER_00: Demand the math.
21:20
SPEAKER_01: And if you want to see what a properly documented, math-backed installation looks like, you know, Dave Hartzall's field notes and standards are a perfect benchmark for how the industry should operate.
21:31
SPEAKER_00: They really are.
21:31
SPEAKER_01: This raises an important question for the future, though.
21:34
SPEAKER_01: Something to kind of mull over.
21:35
SPEAKER_01: Oh, what's that?
21:36
SPEAKER_01: Well, today's deep dive focuses entirely on how the ground moves heat today, relying on 30-year software models and known deep ground temperatures.
21:44
SPEAKER_01: But what happens if climate change and permanently longer, hotter summer droughts fundamentally alter the deep ground soil temperatures over the next two decades?
21:54
SPEAKER_01: Oh, wow.
21:55
SPEAKER_01: Will a perfectly calculated geothermal loop designed in 2026 still have the thermal capacity to keep a house cool in the climate reality of 2056?
22:04
SPEAKER_00: That invisible engine buried under your lawn might be facing a completely different world.
22:08
SPEAKER_00: It's definitely something to think about.
22:10
SPEAKER_00: Till next time.