New Hampshire · N.H. Admin. R. Env-Wq 1010.01
Septic system requirements in New Hampshire
Tank sizes, drainfield rules, setbacks, permits, and real costs — pulled from New Hampshire's own code rather than a national average.
- 3-bedroom tank
- 1,250 gal
- Design flow
- 150 gpd/BR
- Typical install
- $12,000–$30,000
- Permit fee
- $300–$900
- Well setback
- 75 ft
- Permitted by
- State agency
Septic tank sizes required in New Hampshire
New Hampshire sizes systems on a design flow of 150 gallons per day per bedroom. The tank must meet both the bedroom table below and a 2× daily-flow detention requirement — whichever produces the larger number governs.
| Bedrooms | Design flow | Code minimum | Recommended | With garbage disposal |
|---|---|---|---|---|
| 1 bedroom | 150 gpd | 1,250 gal | 1,250 gal | 1,875 gal |
| 2 bedrooms | 300 gpd | 1,250 gal | 1,250 gal | 1,875 gal |
| 3 bedrooms | 450 gpd | 1,250 gal | 1,250 gal | 1,875 gal |
| 4 bedrooms | 600 gpd | 1,250 gal | 1,250 gal | 1,875 gal |
| 5 bedrooms | 750 gpd | 1,500 gal | 1,500 gal | 2,250 gal |
| 6 bedrooms | 900 gpd | 1,750 gal | 2,000 gal | 2,625 gal |
Source: N.H. Admin. R. Env-Wq 1010.01. The recommended column rounds the governing requirement up to a tank size manufacturers actually stock.Run your own numbers →
Drainfield size and cost by soil type
For a three-bedroom home in New Hampshire at 450 gpd. This single table explains most of the variation between quotes — the area scales inversely with how fast your soil accepts water, and the drainfield is the largest line item in the job.
| Soil | Loading rate | Absorption area | With reserve | Typical total install |
|---|---|---|---|---|
| Medium sand | 0.8 gpd/ft² | 563 ft² | 1,126 ft² | $12,100 |
| Sandy loam | 0.5 gpd/ft² | 900 ft² | 1,800 ft² | $15,200 |
| Loam | 0.4 gpd/ft² | 1,125 ft² | 2,250 ft² | $17,300 |
| Silt loam | 0.3 gpd/ft² | 1,500 ft² | 3,000 ft² | $20,700 |
| Clay loam | 0.2 gpd/ft² | 2,250 ft² | 4,500 ft² | $27,600 |
Estimates use New Hampshire's cost index of 1.02× the national average. Build a line-item estimate →
Permits and who issues them
NHDES issues construction and operational approvals statewide; designs must come from a state-licensed Septic System Designer.
| Permit required | Yes |
|---|---|
| Typical fee | $300 – $900 |
| Soil evaluation | Required before permit |
| Licensed installer | Required |
| Turnaround | 3–8 weeks |
| Ongoing inspection | Not mandated statewide |
| Reserve area | 100% replacement area required |
Minimum setback distances
Measured horizontally from the drainfield unless noted. Local rules are frequently stricter, and on a small lot these numbers — not the soil — often decide the layout.
| Private water well | 75 ft |
|---|---|
| Property line | 10 ft |
| Surface water | 75 ft |
| Building foundation | 10 ft |
Regulatory contact
New Hampshire Department of Environmental Services — Subsurface Systems
www.des.nh.gov · 603-271-3501
What makes septic hard in New Hampshire
Shallow bedrock and glacial till mean ledge removal is routine, particularly in the White Mountains and the Monadnock region.
Shoreland Water Quality Protection Act setbacks apply on top of the base septic rules near lakes and rivers.
Small lakefront lots frequently cannot fit both a primary and reserve area.
Things that catch people out
- The tank floor is 1,250 gallons, higher than the national norm, and a garbage grinder pushes it 50% higher again.
- Only a licensed NH Septic System Designer can submit a design — and permits are issued by the state, not your town.
New Hampshire septic questions
What size septic tank do I need in New Hampshire?
A three-bedroom home in New Hampshire requires a minimum 1,250 gallon tank under N.H. Admin. R. Env-Wq 1010.01. Design flow is 150 gallons per day per bedroom, and the tank must also hold 2 times daily flow, so the practical recommendation is 1,250 gallons.
Do I need a permit for a septic system in New Hampshire?
Yes. NHDES issues construction and operational approvals statewide; designs must come from a state-licensed Septic System Designer. Fees typically run $300 to $900, with a turnaround of about 3–8 weeks. A soil evaluation or percolation test is required before a permit is issued.
How much does a septic system cost in New Hampshire?
A conventional system for a three-bedroom home typically runs $12,000 to $30,000 installed. Soil quality moves this more than anything else — on tight clay requiring a mound, budget two to three times the low end.
How far must a New Hampshire drainfield be from a well?
75 feet from a private water well. Local rules can be stricter.
Sources
Every figure on this page traces to one of these documents.
- N.H. Admin. R. Env-Wq 1010.01 — Liquid Capacity of Septic Tanks: Residential Up To 10 Bedrooms · verified 2026-09-18
- N.H. Admin. R. Env-Wq 1000 — Subsurface Systems · verified 2026-09-18