By the team at Homegrown Heating and Air Conditioning.
Working out how to heat a garage in Colorado is not the same problem as heating a bedroom, and the difference is not the cold. It is what a garage holds: gasoline, solvents, paint thinner, a mower with fuel in it, and most days, a running engine.
Put an open flame in that room and rules apply that come up nowhere else in the house. We at Homegrown Heating and Air Conditioning install garage and shop heat across Northern Colorado, and this is the order we work through it.
The Garage Door Is the First Move, Not the Heater
An uninsulated overhead door will defeat any heater you buy. It is the largest single surface in the room, it is thin, and it leaks at the jambs and the bottom seal. Before we quote equipment we look at four things:
- The overhead door, its insulation, its perimeter seal and its bottom astragal
- The ceiling, which in an attached garage is often the floor of a bedroom
- The common wall to the house, and whether the drywall on it is intact
- The slab edge, which loses heat sideways to frozen soil all winter
Skip this and you buy an oversized heater that still leaves the far corner cold.
Why a Garage Is Treated Differently Than Any Other Room
A fuel-fired appliance needs two things from the room it sits in: air to burn, and distance between its ignition source and whatever is on the floor.
Gasoline vapor is heavier than air. It pools low along the slab, exactly where a floor-standing heater keeps its burner and its igniter. That is why the 2024 International Fuel Gas Code requires appliances with an ignition source to sit so the source of ignition is not less than 18 inches above the floor in private garages, unless the appliance is listed as flammable vapor ignition resistant. The same section treats a non-living space opening directly into a private garage as part of the garage, so a storage nook does not escape the rule.
Combustion air is the second half. Section 304 of that code sets how much air a fuel-burning appliance needs, and the standard indoor method asks 50 cubic feet of space per 1,000 Btu per hour of input. A freshly tightened, insulated garage is where that air stops being free, and the appliance must then draw combustion air from outdoors through sized permanent openings.
When either of those goes wrong, the appliance stops burning cleanly and starts making carbon monoxide. In a detached shop that is dangerous. In an attached garage it is worse, because the garage shares a wall and usually a ceiling plane with bedrooms. That is why the residential code also requires ducts in a garage to be sheet steel with no openings into the garage. The envelope is built to keep garage air out of the house, and a bad fuel-fired install fills that air with something you cannot smell.
Attached Garage and Detached Shop Are Two Different Projects
An attached garage shares at least one wall, and often a ceiling assembly, with living space.
A detached shop is its own building; a separate gas line and permit, and a colder shell.
The shortlist differs for that reason alone. Attached garages lean electric. Detached shops with gas already run to them are where a gas unit heater earns its place.
What It Takes to Heat a Garage in Colorado
Northern Colorado sits at about 5,000 feet, and the numbers a garage heater answers to are not mild.
- The 99 percent heating design temperature is about 1 degree F in Larimer County and about 0 degrees F in Weld County.
- Fort Collins runs 5,918 heating degree days a year, so the heating season here effectively runs September through May.
- Elevation changes the job. A shop in Wellington at 5,202 feet is a harder load than the same shop in Greeley at 4,674 feet, because thinner air carries less heat per cubic foot.
Most people do not want 70 degrees in a garage. They want it above freezing, or 60 degrees while they are out there. Those are different sizing problems, and the answer changes the equipment.
The Four Options, and How Each One Fails
Ductless mini split. The efficient answer for an attached garage, and the only one that also cools in July. No combustion, no vent. A cold climate rated unit holds useful capacity well below zero, though capacity falls as the outdoor temperature drops, which is why the load calculation matters. Our ductless mini split page covers how those are specified.
Electric unit heater. Cheap to hang, no venting, no combustion air. It is also the most expensive heat per Btu you can buy here, and a 240 volt heater big enough for a two-car garage may need panel capacity you do not have. Good for intermittent use, poor all winter.
Gas unit heater. The lowest fuel cost where gas already exists, and the usual answer in a detached shop. In exchange it needs a vent, combustion air, clearances, ignition source elevation unless it is listed flammable vapor ignition resistant, and a gas line sized for the load. Its input also has to be adjusted for altitude, required above 2,000 feet and taken from the manufacturer’s high altitude listing.
Radiant tube. A vented gas appliance that heats objects rather than air, which suits a high-bay shop where the door opens repeatedly. It carries every fuel-fired requirement above, plus clearances around lifts, storage and the door track.
Extending the house furnace into the garage is not on this list. Beyond the code prohibition on duct openings into a garage, it puts the garage on the same air loop as the bedrooms and asks a furnace to carry a load nobody sized it for.
One Fort Collins Rule Worth Clearing Up
Fort Collins restricts what can serve as a home’s primary indoor central heating system when that system is all electric. A garage heater is generally not primary central heat, but that call belongs to the building department for your address, so we confirm before specifying. If the project grows into whole-home heat, our heat pump installation and repair page is the better starting point.
For a shop you occupy on weekends, a setback schedule beats extra capacity. Smart thermostat installation pays back faster on a garage than almost anywhere else.
What One Customer Said About How We Diagnose
Josh Porter did not hire us for a garage project. He called about aging heating and cooling equipment, and Dan spent the visit explaining what he was checking rather than steering toward a sale.
“Dan was detailed and took time to show me and describe what he was investigating.”
“I never once felt like he was trying to sell us a new one just trying to ensure the safe function if the unit as long as possible.”
That is the same posture we bring to a garage quote. The heater is the last decision, not the first, and a homeowner who understands why a gas appliance needs combustion air chooses better than one handed a price. Read more customer reviews from Northern Colorado homeowners.
Get a Garage Heating Quote
We look at the door, the ceiling and the slab before the equipment, run the load, and put the options in writing. We are licensed and insured throughout Northern Colorado, and we work seven days a week, 7 a.m. to 7 p.m. Contact Homegrown Heating and Air Conditioning to get on the schedule.
Frequently Asked Questions
Do I need a permit to add heat to my garage in Northern Colorado?
In most cases yes. Fort Collins lists heating, mini splits and heat pumps on its mechanical permit at $65 per heating appliance, and a gas line for a heater requires one. Larimer County names unit heaters, furnaces and gas appliances on its miscellaneous permit list. We pull the permit.
Can I just run a duct from my furnace into the garage?
No. The residential code requires ducts in a garage to be sheet steel with no openings into the garage, because the wall and ceiling between a garage and the living space exist to keep garage air out of the house. A register there defeats that separation, and the furnace was sized without that load.
How warm can I keep a Wellington shop in January?
As warm as you size for, but the envelope decides the price. Wellington sits at 5,202 feet and the 99 percent heating design temperature in Larimer County is about 1 degree F. Holding a shop above freezing is a modest load. Holding 65 degrees in an uninsulated building with a bare door is a much larger one.
Will a mini split keep working in a garage at 5,000 feet in deep cold?
A cold climate rated unit will, if it was sized against the real load rather than by square footage. Heating capacity falls as the outdoor temperature drops, so the unit has to be selected at the design temperature, not at 47 degrees F.
Does the Fort Collins all-electric heating rule apply to my garage heater?
That rule governs a home’s primary indoor central heating system. A unit serving only a garage is generally not that system, but the determination belongs to the building department for your address, so we confirm rather than assume.
Are there rebates for heating a garage in Northern Colorado?
Some. Xcel Energy pays a flat $500 for a non-ducted heat pump in supplemental use such as a garage, at amounts effective October 1, 2026. Poudre Valley REA members have their own heat pump rebate with a 90 day application window, covering much of Wellington and Laporte. Colorado’s heat pump tax credit generally does not reach a garage-only unit.
