Whether your boiler is classified as low-pressure or high-pressure decides who can inspect it, how often, and how involved the inspection is. The good news is that you can usually tell which one you have from the nameplate. Here is how to read it and what each class requires.
Boiler inspection rules are written around the boiler's pressure classification, not its size or fuel. The classification determines three things at once: how often the boiler must be inspected, what the inspection includes, and who is authorized to perform it. Get the classification right and the rest of your compliance plan falls into place. Get it wrong and you can end up on the wrong schedule with the wrong inspector.
The line between low-pressure and high-pressure is set by operating pressure and temperature, following the ASME Boiler and Pressure Vessel Code:
The reason the threshold matters is risk. A high-pressure vessel stores far more energy, so the inspection regime is more frequent and more thorough.
You usually do not have to guess. Look at the boiler's nameplate and its ASME stamp:
The nameplate also lists the maximum allowable working pressure, which confirms the classification against the thresholds above. If the nameplate is missing or illegible, an inspector can determine the classification from the equipment.
Low-pressure boilers, the kind in most residential and commercial heating systems, are the simpler case.
High-pressure boilers carry the heavier requirement.
| Low-pressure | High-pressure | |
|---|---|---|
| Threshold | Steam at or below 15 psi; hot water at or below 160 psi / 250°F | Steam above 15 psi; hot water above 160 psi / 250°F |
| ASME stamp | H-stamp (E-stamp if electric) | S-stamp |
| Frequency | Typically annual | Annual, internal + external ~6 months apart |
| Boiler offline? | Often not required | Required for the internal inspection |
| Who inspects | Licensed installer or authorized insurer (varies) | Authorized insurance company |
For how these schedules play out in practice, see our guide on how often commercial boilers need to be inspected, and for the NYC filing timeline specifically, the NYC boiler inspection deadline.
Check the nameplate and ASME stamp. An H-stamp indicates a low-pressure boiler, an S-stamp indicates a high-pressure boiler, and an E-stamp indicates an electric boiler. The nameplate also lists the maximum allowable working pressure, which confirms the classification.
Often yes. High-pressure boiler inspections are generally performed by an authorized insurance company. Low-pressure inspections, depending on the jurisdiction, may be performed by a licensed qualified installer or an authorized insurance company.
A high-pressure vessel stores much more energy and carries greater risk, so the code requires a more frequent and more thorough inspection, typically an annual internal and external examination performed about six months apart.
No. An HLW-stamped hot water heater is not a boiler and cannot legally provide space heat for a building. It is not subject to the boiler inspection requirements described here.
Send us your equipment details or address and we will confirm whether it is low-pressure or high-pressure, which inspection it needs, and who has to perform it. We handle the inspection and the filing.