Yes, you can convert a wood burning fireplace to gas, and in most Denver metro homes it is a one to three day job, not a rebuild. What decides the cost and the result is not the burner. It is the chimney above it.
There are three real paths: a gas log set in the firebox you already have, a sealed gas insert vented with its own liner, and a full built in replacement. Those are three different appliances, not three price points for one. Whichever you pick, you are changing three systems at once: the appliance, the venting, and the fuel supply.
This guide covers the project itself: the flue question that drives everything, venting, the gas line, permits, your damper, and who should not convert. If you are still choosing a fuel, start with our comparison of gas versus wood burning fireplaces in Colorado.
The Three Conversion Paths, Side by Side
Nearly every conversion we quote in Aurora and Denver lands in one of three buckets, sold as good, better, and best. They are three different appliances sharing one hole in your wall.
A vented gas log set is a burner and ceramic logs in the firebox you own. The firebox stays open, the damper is fixed permanently open, and most of the heat still leaves up the chimney.
A gas insert is a sealed firebox in a steel cabinet that slides into the masonry opening and runs its own liner to the top of the chimney. Our page on gas insert installation in Colorado covers the appliance side.
A full built in replacement pulls the old firebox out, sets a new zero clearance gas fireplace into the framed opening, and rebuilds the face. Failed prefab fireboxes end up here.
Table 1. The three conversion paths compared on efficiency, heat, appearance, and what each asks of the existing flue.
| Factor | Vented gas log set | Sealed gas insert | Built in replacement |
|---|---|---|---|
| What gets installed | Burner and logs in your firebox | Sealed steel appliance inside the firebox | New zero clearance fireplace in the framed cavity |
| Published efficiency | Low, commonly under 25 percent | Commonly 65 to 85 percent | Similar to an insert, by model |
| Heat into the room | Ambience, radiant warmth up close | Zone heat for one or two rooms | Zone heat, sized to the space |
| Appearance | Open firebox, closest to a wood fire | Glass front with a surround on the brick | Rebuilt face, most design freedom |
| Effect on the flue | Keeps the masonry flue, damper locked open | New liner sized to the appliance, plus cap | New vent system, often direct vent |
| Best fit | Occasional decorative use | You want the fireplace to heat | Remodels, failed fireboxes, layout changes |
Those efficiency ranges describe the categories, not any specific model. Manufacturers publish an efficiency rating for each unit they sell, so ask for the number on the model you are quoted rather than trusting the category.
The Flue Question That Decides Everything
This is the part skipped on a lot of sales calls, and the part that costs money two winters later. Wood smoke leaves a firebox hot and rises hard, which is why old fireplaces were built with generous flues. Gas exhaust leaves cooler, moves slower, and carries far more water vapor, so the chimney that served the wood fire is usually the wrong size for the appliance replacing it.
The short version is that an oversized masonry flue cools gas exhaust until it condenses, and that condensate is acidic enough to attack mortar and clay tile from the inside. We walk through that failure mode, and what it looks like on camera, in our guide to furnace and water heater chimney venting.
What matters for a conversion is the decision it forces. A gas appliance needs a vent sized to its own input rating and vent height, taken from the venting tables in the National Fuel Gas Code and the appliance manual, never from the size of the fireplace opening. Liner diameters, materials, and insulation are covered on our chimney lining page.
Two things settle the plan before an appliance is ordered. If the furnace or water heater already shares that flue, relining changes the draft picture for both and the stack has to be evaluated as one system. And nobody sizes a liner from a photo, so a chimney inspection with a camera run top to bottom is the first real step.
Venting Types, and Why the Choice Is Not Cosmetic
Gas hearth appliances come in three venting families. The one you pick changes the liner, the wall penetrations, the efficiency, and in some towns whether the appliance is legal at all.
Table 2. The three gas venting types compared on combustion air, exhaust path, indoor moisture, and fit for an existing wood fireplace.
| Venting type | Combustion air | Exhaust path | Indoor moisture | Fit for a conversion |
|---|---|---|---|---|
| Natural vent, or B vent | Room air | Up a liner above the roof | Leaves with the exhaust, but competes with bath fans for makeup air | Common for log sets, simplest retrofit |
| Direct vent, sealed combustion | Outside air, down the outer coaxial pipe | Out the inner pipe, through the flue or a sidewall | None added, combustion is sealed from the room | Strongest choice for most conversions |
| Vent free, or unvented | Room air | Nowhere, it stays in the room | Adds significant water vapor and combustion byproducts | Restricted or prohibited in many jurisdictions |
Why We Steer Homeowners Away From Vent Free
Vent free looks good on paper because nearly all the fuel energy stays in the room and no liner is needed. The problem is what else stays in the room. Every cubic foot of gas burned releases water vapor, which in a sealed modern house shows up as condensation on windows, damp drywall, and odor. Unvented heaters lean on an oxygen depletion sensor, a shutoff of last resort rather than a ventilation strategy.
Rules differ from one Front Range city to the next, so the building department is the authority for your address. Working carbon monoxide alarms are not optional, and our guide to carbon monoxide and chimney safety in Colorado explains where they belong.
Thin Air, Cold Chimneys, and Gas Flames
Gas appliances are rated at sea level, and at a mile up there is less oxygen in every cubic foot of air. Most manufacturers publish a high altitude model or a derate procedure with a different orifice above a stated elevation, and whoever installs yours has to confirm the right one went in. A unit running rich at altitude soots the glass and produces more carbon monoxide. Thin air works on draft too, so a marginal chimney that barely worked with wood can fail with cooler gas exhaust. One more argument for sealed direct vent.
The Gas Line: Who Runs It and Why the Route Matters
A wood fireplace has no gas supply, so unless somebody stubbed a line in years ago, you are adding one. Gas piping is licensed work in Colorado and belongs to a licensed gas fitter or plumber, coordinated with the hearth install rather than improvised on the day. The route matters more than people expect:
- Pipe sizing. The line has to deliver the appliance input rating at the right pressure with everything else in the house running. That is a calculation from load, length, and fittings.
- Access. Code expects a shutoff valve you can reach without dismantling the fireplace. A valve buried behind finished stone becomes a problem the first time the unit needs service.
- Finish damage. Reaching a fireplace on an interior wall or second story can mean opening drywall or pulling flooring. In a 1900s Denver square with plaster walls, it is the most unpredictable line item.
- Bonding and protection. Flexible corrugated tubing carries its own bonding and protection requirements, and an inspector will look for them.
Scope the gas line before you settle on an appliance location. Moving the fireplace on paper is cheaper than moving it in the framing.
What Happens to Your Damper
With a vented gas log set, the damper must be permanently secured open, usually with a clamp or by removing the plate. That is not optional, because a gas fire behind a closed damper spills combustion products into the room. The tradeoff is a chimney that can never be closed again, so the house gives up conditioned air every hour of the year.
With a gas insert, the damper plate is removed or cut so the liner passes through the throat, which is then sealed with a block off plate. Because the appliance is sealed, that constant air loss goes away.
With a full replacement, the old damper leaves with the old firebox. On any flue that still needs to close, a top sealing damper at the crown is worth pricing while the crew is on the roof.
Permits, Inspection, and the Paper Trail
Converting a wood fireplace to gas is permitted work in essentially every Front Range jurisdiction, and the pattern holds even where the details differ: a mechanical or gas permit covering the appliance and the piping, a pressure test on the new line, and an inspection of the vent and clearances before anything is closed behind finish materials. Skipping it usually surfaces later, when unpermitted gas work stalls a sale or an insurer asks whether the install matched the appliance listing. Because the requirements are set city by city, our overview of Colorado chimney laws and regulations is where to check what applies at your address.
Matching the Path to the House
A pre 1950 brick home with an unlined or early clay tile flue and a 1960s masonry fireplace with an oversized flue both point to a sealed insert with a new liner, which solves the deteriorated flue at the same time. A garden level firebox with a short chimney run points toward direct vent.
Factory built metal fireboxes are their own category. A prefab is a listed system, so anything installed into it has to be approved for it. Our page on prefab fireplace repair in Colorado explains how those get evaluated.
For a typical Front Range masonry fireplace, we rank the paths this way:
- Sealed gas insert with a new liner. Best combination of real heat, controlled cost, and a chimney problem solved permanently. This is what we install most often.
- Full built in replacement. The right call when the firebox has failed, the room is being remodeled anyway, or the size and position of the fire need to change.
- Vented gas log set. Reasonable only when the fireplace is decorative and the flue is already sound.
The Project Sequence From First Inspection to First Fire
A conversion done properly follows an order. When steps happen out of sequence, usually because an appliance was bought before anyone looked up the flue, the project stalls.
- Level 2 inspection with a camera. The flue is scanned top to bottom, the firebox and smoke chamber evaluated, and shared venting identified.
- Repairs scoped first. Crown cracks, flashing leaks, spalled brick, and failed tiles get priced before the appliance, because they decide whether the chimney can host one.
- Appliance selection. Measure the opening, choose the venting type, match the input rating to the room, and pick the surround.
- Gas line design and permit. The gas fitter sizes the run and plans the route, and the permit is pulled with the appliance model on it.
- Liner or vent installation. Usually a roof day. The liner goes in, gets insulated where required, and terminates at a top plate and cap.
- Gas piping and pressure test. The line is run, the shutoff is set where a person can reach it, and the system is tested.
- Appliance set and connected. The unit goes in, the vent connects, clearances are verified against the manual, and a block off plate seals the throat.
- Inspection and commissioning. The inspector visits, then the installer fires the unit, checks the flame pattern, confirms the high altitude orifice, and tests the controls.
- Finish work and walkthrough. Trim, surround, patching, then a walkthrough on operation and the shutoff location.
A converted fireplace still needs annual attention. Pilot assemblies, glass gaskets, blowers, vent terminals, and liner caps need eyes on them once a year, and our page on gas fireplace installation and service covers that visit.
Budgeting the Conversion and Comparing Bids
Conversion pricing swings widely because the chimney work does, not because the appliances do. Two neighbors with identical fireplaces land in different places once one flue needs a full liner and a crown rebuild. Current figures live on the chimney and fireplace pricing page rather than in an article that ages. Holding two or three bids, ask each contractor, in this order:
- Does this include a liner sized to the appliance, and what diameter and material?
- Is the gas line included, who runs it, and is the permit in your scope or mine?
- What happens to the damper, and is a block off plate included?
- Which appliance model, and is it the high altitude version?
- What chimney repairs did you find, and what is excluded from this number?
- Who comes back if the unit soots or shuts down in January?
A bid dramatically lower than the others is usually a bid without a liner. That is the item dropped to win the job, and the costliest to add later.
Who Should Not Convert
We talk people out of this project several times a year, and the reasons repeat.
- Homeowners who still want to burn wood. A conversion is not easily reversible. Once the liner is sized for gas and the firebox holds a sealed appliance, going back means undoing all of it.
- Anyone with a structurally unsound chimney. Leaning stacks, open cracks, or a failed crown come first. An appliance bolted to a failing structure is a bad investment.
- Owners of a prefab with no listing information. If nobody can identify the system, nothing can be legally installed into it.
- Anyone expecting a log set to cut the heating bill. It will not. A sealed insert is the only path that gets you there.
- Historic homes with decorative coal era fireboxes. Some were never built to hold a fire of any size.
None of that means the fireplace sits unused. Sometimes the right answer is repairing the wood burning setup instead.
Frequently Asked Questions
Can I convert my wood fireplace to gas without relining the chimney?
Sometimes, with a vented log set, if the flue is sound and correctly sized. For a sealed insert, almost never. It needs a dedicated liner sized to its rating, and that liner protects the masonry from acidic condensation.
How long does a gas fireplace conversion take?
A vented log set in a chimney that already passed inspection takes a few hours. A sealed insert with a new liner is typically one working day, plus time for the gas line and the inspection. A full replacement runs several days.
Do gas logs give off real heat, or are they just for looks?
A vented log set warms whoever sits in front of it, but most of the energy goes up the flue and the damper stays open permanently, so the house loses conditioned air around the clock. To heat a room, use a sealed insert.
Can I still burn wood after the conversion?
Not with an insert, a replacement unit, or a gas log set. Once a gas appliance and its supply line are in the firebox, wood is out. Treat the conversion as permanent, because reversing it means removing the liner too.
Does a gas conversion need a permit in Colorado?
In essentially every Front Range jurisdiction, yes. Expect a permit covering the gas piping and the appliance, a pressure test on the new line, and an inspection of the vent and clearances before finish materials go back on.
My furnace and water heater vent into the chimney. Does that change the plan?
Yes, significantly. Adding an appliance or installing a liner changes draft conditions for whatever else shares that stack, and appliances that were venting acceptably can start spilling. Shared venting must be evaluated as one system first.
Ready to Plan Your Conversion?
The first move is always the same: get a camera down the flue and find out what you have. Everything after that, the appliance, the liner, the gas line, the permit, follows from real information instead of a guess. We look at fireplaces across Aurora, Denver, and the Front Range every week, and we will tell you plainly when a conversion is the right project.
Call Adam Chimney Sweep at (720) 207-9232 to schedule an inspection and get a conversion plan for your fireplace.
