You've laid out the insulation and your PEX pipes are in place. Now, there's only one thing standing in between you and your concrete pour.
You've got to get inspected.
For first-time in-floor heating system installer, that can be a little intimidating. What is the inspector looking for? Are they going to measure each loop? Are they going to check the bend of every tube? Are they going to ask you to explain everything about your system?
Usually, the inspection goes much more straightforward than that.
The goal of an inspection is to simply verify that the components that are about to be covered in six inches of cement have all be safely and accurately installed according to applicable codes, system design, and manufacturer's instructions.
In other words, the inspector is your friend and wants to make sure everything looks right before it disappears beneath your floor.
Please note: Building codes, permit requirements, inspection procedures, and pressure-testing requirements can vary by state and local jurisdiction. Always check with your local Authority Having Jurisdiction (AHJ) before beginning your project.
When Does an Underfloor Inspection Happen?
For a slab-on-grade radiant heating system, inspection typically takes place after the insulation, reinforcement (rebar), radiant tubing, and other components that will be embeded in or beneath the slab are installed, but BEFORE the concrete is poured.
The reason is simple (and obvious): once the concrete truck arrives, correcting something underneath the slab becomes considerably more complicated. So what might the inspector want to see?
1) Is the Correct Tubing Being Used?
An inspector may verify that the tubing is approved for hydronic heating and appropriate for the temperatures and pressure involved in the system. PEX is commonly used for radiant-floor heating because it can be installed in long, flexible circuits with very few connections. (Learn more about the different types of PEX tubing here).
The tubing should also be installed to manufacturer's instructions. Those instructions matter because different manufacturers can specify different requirements for bend radius, fastening, and testing.
2) Is the Tubing Properly Secured?
Concrete is heavy!
More importantly, placing concrete can create a surprising amount of movement beneath the crew's feet. Tubing that looked perfectly positioned the night before the pour can shift if it hasn't been properly secured. An inspector may therefore look at how the PEX is held in position and whether the installation method is appropriate for the system being used.
The goal is to keep the tubing where the system design intended it to be throughout the pour. This is another place where a radiant panel system can simplify installation. Insulations like Heat-Sheet provide a consistent structure for routing and holding the tubing.
3) Is the Insulation Installed Correctly?
Speaking of insulation, radiant heating is supposed to send heat into the living space, and insulation helps with that. That's why insulation and thermal separation are important parts of radiant-floor construction.
Depending on the project and applicable energy code, the inspector may need to verify insulation beneath or around the heated slab before it becomes inaccessible. Hydronic mechanical code provisions also address thermal barriers for radiant-floor systems and require tubing placement to follow the manufacturer's instructions and system design.
4) Are Slab Transitions Protected?
Pay particular attention to the areas where your PEX tubing leaves the floor and travels toward the mechanical equipment or manifold. Those transition points can be vulnerable during construction.
An inspector may look for appropriate protection where tubing passes through or exits concrete and for an installation that prevents the tubing from being damaged by sharp edges, movement, or other construction activity. (The H4 is specifically designed to help protect your PEX before, during, and after installation).
5) Are There Unnecessary Connections Beneath the Floor?
One of the advantages of PEX is its ability to create long radiant circuits without requiring numerous fittings. Where possible, radiant loops are commonly installed as continuous tubing runs from the supply side of the system, through the floor, and back to the return.
That means fewer potential connection points buried beneath finished concrete.
Applicable mechanical codes and manufacturer instructions determine which joints and fittings are acceptable when tubing is embedded, so this is another area where following the approved system design matters. From an installation standpoint, however, the principle is refreshingly simple:
The fewer mysteries beneath the concrete, the better!
6) Has the Radiant Tubing Been Pressure Tested?
This may be one of the most important checks before the pour. Pressure testing helps confirm that the tubing and connections are intact before they become buried beneath several inches of concrete.
But here's an important point:
There isn't one pressure-testing instruction you should pull from the internet and use for every radiant installation.
Model codes, adopted local codes, tubing manufacturers, system components, and the inspector can establish different requirements!
For example: the 2018 International Residential Code includes specific hydrostatic test requirements for hydronic and embedded radiant piping. Uponor's radiant installation handbook provides its own recommended testing procedure (60 psi for at least 24 hours, btw), while explicitly telling installers to check local building codes for additional requirements. Viega likewise provides manufacturer-specific pressure-testing procedures and directs installers to check local code requirements.
That's why your best course if to confirm the required procedure before your inspection day. Ask your local inspector what they expect and follow the requirements of your tubing and system manufacturers. Don't guess!
7) Can the Inspector Actually See the Work?
This may be an obvious one, but it's important. It an inspection is required before work is concealed, the work needs to remain accessible until it's been approved. Minnesota (HUG Hydronics' home state), has inspection rules that state that permitted work must remain accessible and exposed for inspection and cannot proceed beyond the required inspection point until approval is received.
So, resist the temptation to get ahead of schedule. Don't cover portions of the project because you're confident they're correct. Don't let the concrete crew begin to pour before require approvals have been completed. An inspection is considerably easier when the inspector can actually inspect the installation.
Before the Inspector Arrives
A little prep work can make the inspection day uneventful, which is exactly what both you and the inspector want.
Before calling for inspection, verify that your tubing layout is complete, the PEX is securely held in position, insulation is installed, transitions are protected, require pressure testing has been completed, and manufacturer documentation is available if needed.
Take pictures, too! Actually, take a lot of pictures!
Photograph each room and tubing circuit before the concrete is poured. Take several wide shots showing the overall layout and closer photos around walls, doorways, plumbing penetrations, mechanical areas, and other important locations. You'll breathe easy knowing exactly where those PEX tubes are placed when you start framing up your building.
What Happens After Your Pass?
An approved inspection doesn't mean the tubing is suddenly indestructible. There is still a concrete pour between you and your finished radiant floor.
Keep exposed tubing protected, make sure other trades understand that radiant tubing is present, and follow the tubing manufacturer's instructions regarding whether the system should remain pressurized during the pour.
For example, Uponor recommends maintaining pressure during slab placement because a pressure change can help identify damage that occurs during construction.
Pay attention to tubing near slab penetrations and wherever it enters or exits the concrete. This is one of those moments when a few minutes of caution can protect an installation designed to stay beneath your floor for decades.