Radon Mitigation and Plumbing Considerations in New Hampshire

New Hampshire has one of the highest radon concentrations in the United States, with the New Hampshire Department of Environmental Services (NHDES) reporting that roughly 40% of homes tested in the state show radon levels at or above the EPA action level of 4 picocuries per liter (pCi/L). Radon mitigation intersects directly with plumbing systems through sub-slab depressurization piping, drain tile loop configurations, and water supply treatment when radon enters through private wells. This page describes the service landscape governing radon mitigation work in New Hampshire as it relates to licensed plumbing operations, permit obligations, and system-level decision points.

Definition and scope

Radon is a naturally occurring radioactive gas produced by the decay of uranium in soil and bedrock. In New Hampshire, the granite-heavy geology of the White Mountains and surrounding regions generates elevated radon concentrations in both soil gas and groundwater. Radon enters structures through foundation cracks, slab penetrations, and — critically for plumbing professionals — through private well water supplies that release radon gas upon household use.

The regulatory boundary separating radon mitigation from plumbing work depends on the system component involved:

• Sub-slab depressurization (SSD) systems — PVC pipe routed through or beneath a concrete slab to a dedicated exhaust fan. These systems are classified under radon mitigation contractor work, governed by the EPA's Radon Contractor Proficiency (RCP) Program and credentialed through the National Radon Proficiency Program (NRPP) or the National Radon Safety Board (NRSB).
• Radon-in-water treatment systems — Aeration units, granular activated carbon (GAC) filters, and point-of-entry treatment devices installed on pressurized water supply lines. This work is classified as plumbing and falls under RSA 329-A, New Hampshire's statute governing the plumbing licensing board.

The New Hampshire Plumbing Board, operating under the Office of Professional Licensure and Certification (OPLC), holds jurisdiction over licensed plumbers installing or modifying water treatment equipment connected to building water supplies. Installation of point-of-entry radon treatment devices requires a licensed master or journeyman plumber when work involves potable water supply connections. For full context on the regulatory context for New Hampshire plumbing, the OPLC is the authoritative body.

How it works

Radon mitigation in a residential or commercial building follows one of two primary pathways depending on the entry route.

Pathway 1: Soil-gas entry (sub-slab or crawl space)

1. A radon measurement professional tests indoor air using a certified short-term or long-term detector.
2. If levels exceed 4 pCi/L (EPA action level), a mitigation contractor designs an active soil depressurization system.
3. One or more suction points are drilled through the slab or into a drain tile loop.
4. Schedule 40 PVC pipe routes through or alongside the foundation and up through conditioned space or the exterior wall to an inline exhaust fan above the roofline.
5. The fan creates negative pressure below the slab, diverting soil gas before it enters occupied space.

The PVC pipe routing in SSD systems can intersect plumbing rough-in zones, requiring coordination between the radon contractor and the licensed plumber to avoid conflicts with drain lines, water mains, and mechanical penetrations.

Pathway 2: Radon in private well water

Radon dissolved in groundwater is released as a gas when water is agitated — during showering, dishwashing, or flushing. NHDES guidance identifies private well water as a radon exposure pathway requiring testing separate from air testing. Treatment options include:

• Aeration systems — A motorized aeration unit mixes water with air, volatilizing radon before water enters the distribution system. These require a licensed plumber for supply-line integration and a certified electrician for the motor circuit.
• Granular activated carbon (GAC) filters — Whole-house point-of-entry carbon filters adsorb radon but accumulate radioactive decay products over time, requiring disposal protocols. The NHDES Well Water Program provides water-specific guidance.

Further detail on plumbing intersections with private water supplies appears on the New Hampshire Private Well Plumbing Requirements page.

Common scenarios

Three scenarios account for the majority of radon-plumbing intersections in New Hampshire:

Scenario A: New construction with integrated radon-ready rough-in
The 2015 International Residential Code (IRC), adopted in New Hampshire with state amendments, includes Appendix F provisions for radon-resistant new construction (RRNC). A passive radon pipe — typically a 3-inch Schedule 40 PVC stack — is installed during rough-in, running from beneath the slab to above the roofline. The licensed plumber coordinating rough-in work must account for this stack when laying out drain and vent stacks to avoid conflicts.

Scenario B: Retrofit mitigation in an existing structure
A certified radon mitigator cores through an existing slab and routes new PVC piping through finished mechanical spaces. When the routing path conflicts with drain lines, supply mains, or existing plumbing chases, the plumbing contractor and radon contractor must coordinate. Penetrations through fire-rated assemblies require proper fire-stopping consistent with New Hampshire's adopted building code.

Scenario C: Elevated radon in private well water
A property owner on a drilled well tests water and receives results above 2,000 pCi/L — the NHDES recommended remediation threshold for radon in water — and installs a point-of-entry aeration or GAC system. A licensed plumber performs the supply-line bypass, pressure vessel connections, and drain tie-in for the aeration unit's discharge. This work falls squarely within plumbing licensure scope under RSA 329-A.

Decision boundaries

Determining which licensed professional is responsible for a given radon-related installation requires evaluating four factors:

1. Connection to potable water supply
Any penetration, modification, or connection to a pressurized potable water supply line requires a licensed plumber. Radon treatment units — regardless of whether the installer holds an NRPP or NRSB mitigation certification — must be plumbed in by or under the direct supervision of a New Hampshire-licensed plumber.

2. Soil gas vs. water-borne radon
SSD systems (soil gas) are governed primarily by radon contractor certification, not plumbing licensure. Water treatment systems (waterborne radon) fall under plumbing licensure. A building with both elevated air radon and elevated water radon may require both types of certified professionals operating independently on the same project.

3. Permitting obligations
New Hampshire does not maintain a single statewide radon contractor licensing statute as of the regulatory framework established under RSA 329-A, but building permit requirements vary by municipality. Structural penetrations through foundation slabs and exterior walls typically require a building permit from the local building department. Point-of-entry water treatment installations may require a plumbing permit depending on local amendments to the adopted plumbing code. Professionals should verify permit requirements with the municipal building official before commencing work. The New Hampshire Plumbing Code page describes the state's adopted code framework.

4. Geographic scope and limitations
This reference covers radon mitigation as it intersects with plumbing practice within the state of New Hampshire. Federal EPA radon standards and voluntary programs (RCP, NRPP, NRSB certification) apply nationally and are not specific to New Hampshire. Local ordinances in municipalities such as Manchester, Nashua, or Concord may impose additional permit requirements beyond the state baseline. Properties served by public water systems rather than private wells fall outside the water-borne radon scope described here, as radon treatment for public water supplies is governed by the EPA's Radon in Drinking Water Rule rather than individual property plumbing decisions. Commercial properties follow a separate permit and inspection pathway described on the New Hampshire Commercial Plumbing Requirements page.

The full landscape of licensed plumbing practice in New Hampshire — including master and journeyman license classifications, reciprocity, and continuing education requirements — is organized at the New Hampshire Plumbing Authority index.

References

• New Hampshire Department of Environmental Services — Radon Program
• New Hampshire OPLC — Plumbers Licensing Board
• RSA 329-A — New Hampshire Plumbing Licensing Statute
• U.S. EPA — Radon: A Citizen's Guide to Radon Reduction
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