Gas fireplace permits, gas piping rules, and altitude in Larimer and Weld County

Two things decide whether a gas fireplace job in northern Colorado is done correctly: who permitted it and whether anyone adjusted it for altitude. Repairs need no permit anywhere in Larimer or Weld County. New appliances and new gas piping need one everywhere, and the rules differ by jurisdiction because Fort Collins, Loveland, Larimer County, Weld County, and half a dozen towns each run their own building department. Altitude is simpler and more often ignored: every community on this page sits above the elevation where the National Fuel Gas Code calls for derating a gas appliance.

What needs a permit, and what does not

Not permitted: replacing a thermocouple, thermopile, pilot assembly, ignition module, gas valve, blower, remote receiver, wall switch, glass, or gasket on an existing appliance. That is service work on equipment that was already permitted and inspected.

Permitted: a new or replacement fireplace, insert, or stove; a gas log set installed into a masonry fireplace; and any new, extended, or altered gas piping. Those change the appliance or the fuel system, and both are inspected.

Larimer County (unincorporated: Laporte, rural addresses)

Larimer County’s Building Department publishes a list of work that requires a Miscellaneous Permit, and three entries on it cover this trade: Fireplace, Gas Log Inserts, and Gas Line & Gas Appliances. Propane tank installation and replacement is on the same list, which tells you how common tanks are outside the mains. If your address is unincorporated, this is your permit, whether you are in Laporte, on a county road outside Wellington, or up the canyon.

Fort Collins

Fort Collins Building Services runs its own permits and its own trade licensing. The city’s building permit guidance lists “Fireplace, Wood Stove or Fire Pit” as permitted work, notes that a heating device installed in a previously unheated space goes in as a remodel or alteration permit rather than a fast-track permit, and says that when a gas line is installed for a heater, a mechanical permit is submitted.

The licensing side is worth knowing because it is unusually specific. Among the city’s specialized trade contractor licenses are a Fireplace Appliance license, for installing non-portable listed manufactured fuel-burning fireplace appliances and their chimneys or vents as regulated under the mechanical code, and a Gas Piping license, for installing piping and fittings supplying fuel gas and for water heater replacement under the mechanical code the city has adopted. Those two licenses describe the gas fireplace trade almost word for word. Ask any bidder which of them they hold.

Loveland

Loveland runs its own Building Division, separate from both Fort Collins and Larimer County, and permits plumbing and fuel gas piping work with inspections, including the gas line and venting on a gas appliance install. The city licenses mechanical contractors through its National Standard Master Mechanical license. A crew licensed in Fort Collins is not automatically licensed in Loveland, and the reverse is equally true.

Weld County and its towns

Weld County adopted the 2024 International Building, Residential, Mechanical, Plumbing and Energy Conservation Codes and related standards, effective June 15, 2026. That is the code your inspection is measured against on the Weld side of the line, which matters in Johnstown and Berthoud, where the county line runs through town.

The towns each add their own layer:

• Johnstown lists a new or replacement fireplace as permitted work, alongside plumbing, electrical, and new or replacement furnaces, water heaters, and air conditioning. Permits go through the town’s eTRAKiT portal, code and inspection questions go to SafeBuilt, and every contractor must hold a Town of Johnstown license. The town enforces the 2024 International Building, Residential, Mechanical, Fuel and Gas, Plumbing, Fire and Energy Conservation Codes plus the 2023 National Electrical Code.
• Milliken requires permits for electrical, gas, mechanical, and plumbing system work and names gas fireplaces among its counter permit categories. A Colorado licensed electrician or plumber must perform that work unless a homeowner files a notarized affidavit for their own residence, and contractors must first hold the town license required under Municipal Code Chapter 6, Article IV.
• Severance and Berthoud each run their own building and permits function inside town limits.
• Greeley and Windsor likewise permit through their own departments.

Colorado’s gas piping rule

Gas piping is not a fireplace accessory in Colorado. Fuel gas piping falls under the State Plumbing Board’s rules (3 CCR 720-1), and it is regulated at the state level. Colorado licenses plumbers through the state, and local jurisdictions layer their own permits and inspections on top. Milliken’s own permit page states the rule as plainly as anyone: a Colorado licensed plumber must perform the plumbing work unless a homeowner files a notarized affidavit for their own home. Fort Collins encodes the same division by issuing a separate Gas Piping trade license.

What this means on a quote: extending a gas line to a masonry fireplace for a log set, or running a new line for an insert, is separate permitted, inspected, pressure-tested work with its own licensing. It is why the pricing page quotes a log set installation as “$600 to $1,800 plus gas line” instead of pretending the line is free.

The altitude derate

The National Fuel Gas Code (NFPA 54 / ANSI Z223.1) calls for derating gas appliances installed above 2,000 feet by about 4 percent per 1,000 feet, and manufacturers implement that with high-altitude orifices and conversion kits published by elevation band, with natural-gas kits typically starting above 4,500 feet. Making the adjustment is the installer’s responsibility, and it is the single most commonly skipped step in this trade.

Every community this site covers is in the band:

A unit that never got its kit runs rich: lazy yellow flames, soot on the glass that returns within a week of cleaning, delayed ignition with a whump, and more carbon monoxide. A unit fitted with an orifice for the wrong band runs weak and short. Both look like a fireplace problem and are really an install-day problem, which is why a good tech checks orifice size against the elevation and the fuel on any repair.

Propane versus natural gas

Xcel Energy is the natural gas utility named on Larimer County’s utility-provider list, Greeley is Atmos Energy territory, and addresses off the mains run propane from a tank. Propane is delivered at higher pressure through smaller orifices, so a propane appliance needs propane-specific orifices, pilot assembly, and valve, plus a regulator at the tank that is part of the inspection.

The consequences are not theoretical. The Consumer Product Safety Commission’s record includes a December 2008 recall of Napoleon propane GDI44 gas fireplace inserts, where a build-up of propane and delayed ignition could break the glass, and a June 2014 recall of Napoleon GD3200-P and GD3200B-P propane fireplaces for the same class of hazard. In both cases the natural gas versions of the same appliance were not affected. That is what the fuel-specific parts are protecting against, and it is why “propane or natural gas?” is one of the first questions on any call. The safety inspection and leak check at $125 to $250 covers the regulator, the fittings, and a carbon monoxide reading.

Sources: Larimer County Building Department permit list; City of Fort Collins building permit and contractor licensing pages; City of Loveland Building Division; Weld County Building Department code adoption; Town of Johnstown building inspections and permits; Town of Milliken building application page; CPSC recall records 09063 and 14218.