HVAC Ventilation Standards and Requirements in New Hampshire
Ventilation standards in New Hampshire govern how residential and commercial buildings exchange stale indoor air with conditioned outdoor air, controlling moisture, combustion byproducts, and airborne contaminants. These requirements draw from a layered framework of state-adopted building codes, ASHRAE standards, and mechanical codes enforced through the New Hampshire Office of Professional Licensure and Certification (OPLC) and local building departments. Proper ventilation directly affects occupant health, equipment performance, and code compliance — making it a central element of any new construction or retrofit HVAC project in the state.
Definition and scope
Ventilation in the HVAC context refers to the controlled movement of air into, out of, and within a building — distinct from infiltration, which is uncontrolled air leakage through the building envelope. New Hampshire has adopted the 2018 International Energy Conservation Code (IECC) and the 2015 International Mechanical Code (IMC) as the primary regulatory frameworks for residential and commercial construction, administered through the New Hampshire Building Code Review Board.
Ventilation requirements in these codes cover three distinct system categories:
- Whole-building ventilation — continuous or intermittent dilution of indoor air through a mechanical system, typically a heat recovery ventilator (HRV) or energy recovery ventilator (ERV)
- Local exhaust ventilation — point-source removal of contaminants from kitchens, bathrooms, and utility rooms
- Combustion air ventilation — dedicated air supply for fuel-burning appliances including furnaces, boilers, and water heaters
ASHRAE Standard 62.2-2022, Ventilation and Acceptable Indoor Air Quality in Residential Buildings, sets the minimum whole-building ventilation rates adopted by reference in the 2015 IMC. For residential buildings, that standard specifies a base ventilation rate of 1 CFM per 100 square feet of floor area plus 7.5 CFM per occupant (ASHRAE 62.2-2022).
The scope expands in commercial and mixed-use buildings, where ASHRAE Standard 62.1-2016 applies, prescribing per-person and per-floor-area ventilation rates by occupancy type — from 5 CFM per person in storage spaces to 10 CFM per person in offices.
How it works
Mechanical ventilation systems in New Hampshire's climate must balance air quality against energy loss, particularly relevant given the state's heating-dominated climate profile. An HRV transfers heat from outgoing exhaust air to incoming fresh air without mixing the two air streams, recovering 70–80% of thermal energy in well-performing units. An ERV performs the same function while also transferring moisture, which is advantageous in tight, well-insulated buildings prone to low winter humidity.
The permitting and inspection pathway for ventilation systems in New Hampshire follows a structured sequence under the IMC and the state's adopted residential code:
- Design submission — mechanical drawings specifying duct sizing, CFM ratings, equipment specifications, and combustion air calculations submitted to the local building department
- Plan review — building official or designee verifies compliance with adopted code editions
- Rough-in inspection — ductwork and equipment placement verified before insulation or wall closure
- Final inspection — airflow testing or commissioning documentation reviewed; for commercial projects, a Test and Balance (TAB) report is commonly required
Licensed contractors performing duct installation and mechanical work in New Hampshire must hold credentials issued through the NH OPLC, relevant to the scope of work — a topic covered in detail under NH HVAC licensing requirements and NH HVAC permits and inspections.
Common scenarios
New residential construction under the 2018 IECC requires whole-building mechanical ventilation in tightly sealed homes achieving 3 ACH50 or less in blower door testing. In these structures, passive infiltration cannot meet ASHRAE 62.2 minimums, making an HRV or ERV a practical requirement rather than an option.
Existing home retrofits — particularly after air-sealing as part of weatherization programs — frequently trigger ventilation deficiencies. A home sealed from 10 ACH50 to 4 ACH50 may no longer provide adequate natural air exchange, requiring post-retrofit mechanical ventilation installation. The New Hampshire Office of Energy and Planning (OEP) supports weatherization programs that interact directly with ventilation adequacy assessments.
Bathroom and kitchen exhaust must meet IMC minimum capacities: bathrooms require either 50 CFM intermittent or 20 CFM continuous exhaust; kitchen range hoods require 100 CFM intermittent or 25 CFM continuous at minimum. These figures are structural code requirements under Section 403 of the 2015 IMC.
Combustion air for heating equipment is governed by IMC Chapter 7, which specifies the required free area of combustion air openings based on total BTU/hr input of all appliances in a confined space. This is a safety-critical calculation; undersized combustion air can cause negative pressure conditions that pull flue gases back into occupied spaces — a backdrafting failure mode relevant to forced-air furnace systems and boiler systems.
Decision boundaries
Choosing between an HRV and ERV depends on building tightness, occupancy load, and seasonal moisture patterns. HRVs are generally preferred in New Hampshire's cold-dry winter conditions, where moisture recovery is less critical and sensible heat recovery takes priority. ERVs become more appropriate in mixed or humid climates, or in buildings where occupancy-driven moisture generation is high.
A comparison of system thresholds under ASHRAE 62.2:
| Condition | HRV Preferred | ERV Preferred |
|---|---|---|
| Climate zone 6 (most of NH) | Yes | Conditional |
| Tight envelope (<3 ACH50) | Yes | Yes |
| High occupancy load | Conditional | Yes |
| Dry winter interior humidity | Yes | No |
Ventilation design also intersects with ductwork design and indoor air quality management, particularly when dedicated ventilation systems share ductwork with heating and cooling equipment — a configuration that requires careful attention to ASHRAE 62.2-2022 intermittent ventilation credits and duct leakage standards under the adopted IECC.
Local building departments in New Hampshire retain authority to apply stricter standards than state minimums. Municipalities including Manchester, Nashua, and Concord have active plan review processes that may require supplemental documentation beyond state-level submissions.
References
- New Hampshire Office of Professional Licensure and Certification (OPLC) — Building Code Review Board
- ASHRAE Standard 62.2-2016 — Ventilation and Acceptable Indoor Air Quality in Residential Buildings
- ASHRAE Standard 62.1-2016 — Ventilation for Acceptable Indoor Air Quality (Commercial)
- 2018 International Energy Conservation Code (IECC) — ICC
- 2015 International Mechanical Code (IMC) — ICC
- New Hampshire Office of Energy and Planning (OEP)