Aftermarket Exhaust in New Hampshire
Replacing the exhaust system is legal in New Hampshire, but a muffler in good working order is required and cutouts or bypasses are prohibited. There is no statutory 'no louder than stock' rule — the standard is that the exhaust must not produce excessive or unusual noise.
Verified against primary sources · August 2026
What the law says
Replacing the exhaust system is legal in New Hampshire, but a muffler in good working order is required and cutouts or bypasses are prohibited. There is no statutory 'no louder than stock' rule — the standard is that the exhaust must not produce excessive or unusual noise. Removing the catalytic converter is prohibited by federal law (Clean Air Act § 203) regardless of state rules. New Hampshire expressly bans straight pipes, with escalating fines of $100, $250, and $500. Annual safety and OBD inspection applies. (RSA 266:59-a sets decibel limits for motorcycles only.)
Specific Limits
- Cutouts
- prohibited
- Muffler required
- Yes
- Louder than stock
- not addressed; excessive noise standard applies
- Catalytic converter
- removal prohibited by federal law
Frequently Asked Questions
Are aftermarket exhaust legal in New Hampshire?
What are the exact aftermarket exhaust limits in New Hampshire?
Street-legal aftermarket exhaust picks
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