Fireplace Insert Buying Guide: Gas, Wood & Electric Inserts

If you have an open masonry fireplace, you own one of the least efficient heating features ever built — and one of the easiest to fix. A fireplace insert is a sealed heating appliance that slides into your existing firebox and turns a decorative, heat-losing hole in the wall into a genuine heat source. This guide covers the two things that decide the project: which fuel to choose, and how to size and vent the insert to your existing fireplace.

At Urban Supply, we carry fireplace inserts from Napoleon, Empire Comfort Systems, Kingsman, Dimplex, SimpliFire, and Majestic — over 120 in-stock models in gas, wood, and electric, from about $155 to $6,199. First, understand why the upgrade is worth it.

Why an Insert Beats an Open Fireplace

An open masonry fireplace is only about 5–10% thermally efficient. Worse, because open combustion pulls heated room air up the chimney, an open fire can actually create a net heat loss — cooling the rooms not directly in front of it while it burns. You are, in effect, sending your furnace's warm air up the flue.

A sealed insert flips that math. By enclosing the fire in a firebox with its own controlled air supply and radiating heat back into the room, inserts reach:

Wood inserts: roughly 65–75% efficient (non-catalytic) up to 72–83% (catalytic). Gas inserts: about 70–85% for direct-vent models. Pellet inserts: around 75–85%. In practical terms, a modern insert is roughly six to seventeen times more efficient than the open fireplace it replaces. That is a real dent in your heating bill, not a marketing number.

Choose Your Fuel

Gas inserts are the most popular retrofit: flip a switch or press a remote, get instant flame and steady heat, and never touch a log or clean out ash. Direct-vent gas inserts (like Napoleon's Oakville and Roxbury series and Empire's lineup) pull combustion air from outside and vent exhaust back out through a coaxial pipe run up the existing chimney, so they are sealed from your room air and highly efficient. Gas is the right pick for convenience-first buyers who want dependable heat with minimal effort.

Wood inserts are for people who want the authentic fire — the crackle, the aroma, the radiant heat — but with modern efficiency and far less smoke than an open hearth. EPA-certified wood inserts (such as Napoleon's Oakdale EPI3) burn cleanly and throw serious heat, making them excellent for whole-room or zone heating, especially where firewood is cheap or free. The trade-off is the work: loading wood, tending the fire, and removing ash.

Electric inserts are the simplest of all — they slide into the opening, plug in, and produce flame effect plus supplemental heat with no venting, no gas line, and no chimney work. Dimplex and Napoleon electric inserts are ideal when you want ambiance and a little warmth without the cost and complexity of a vented install, or in a home where gas and wood are not options. For a deeper look at electric-only options, see our electric fireplace buying guide.

Sizing: Measure Your Firebox First — Every Time

An insert has to physically fit inside your existing masonry opening, so this is not a step you estimate. Before you shop, measure your firebox and write down all of these: width at the front, width at the back (masonry fireboxes are usually narrower at the rear), height at the front, height at the back, and depth. Inserts are specified with minimum opening dimensions; your firebox must meet or exceed them.

Then match the insert's heat output to the space you want to warm. A small insert sized for a large, open floor plan will run flat out and still leave you cold; an oversized unit in a small room will drive you out. Manufacturers publish a heating-area range (in square feet) and a BTU rating for each model — pick one whose range brackets your room, accounting for ceiling height, insulation, and climate. When you are between sizes for a primary heat source, size up slightly; for pure ambiance with a little warmth, size to the room.

Venting: The Detail That Makes or Breaks the Install

Gas and wood inserts must vent. The standard modern approach is a direct-vent or lined-flue system: a stainless liner is run from the insert up through your existing chimney to carry exhaust out and, in sealed direct-vent designs, draw combustion air in. This liner is not optional — it is what makes the insert efficient and safe, and it is the part of the job most homeowners forget to budget for. Wood inserts likewise require a properly sized liner for a clean, strong draft.

Electric inserts need no venting at all — just an appropriate electrical circuit. That is the single biggest reason electric is the easiest and cheapest insert to install: no liner, no gas line, no chimney work.

Because gas and wood installs involve venting, gas connections, and clearances, they should be installed by a qualified professional. Factor professional installation and the chimney liner into your total budget from the start.

Efficiency and Emissions Standards

Modern wood and pellet inserts sold today must meet EPA Step 2 New Source Performance Standards, which cap particulate emissions at no more than 2.0 grams per hour (crib-wood test basis; 2.5 g/hr under the alternative cordwood test method). That standard is why a new EPA-certified wood insert burns dramatically cleaner than an old fireplace or a decades-old stove — less smoke, less creosote, more heat from every log. If reducing wood smoke matters to you (or to local air-quality rules), an EPA-certified insert is the way to burn wood responsibly.

Fireplace Insert Comparison

Installation and What It Costs

Insert installation ranges from plug-and-play to a professional project, depending on fuel. An electric insert is the simple end: confirm the firebox opening fits, slide it in, and plug it into an appropriate circuit — many homeowners handle this themselves. Gas and wood inserts are professional installs. Both require a stainless chimney liner run from the insert up through your existing masonry chimney, and gas units also need a gas line connection. A qualified installer will confirm clearances, size and install the liner, connect and pressure-test the gas, and verify safe draft and operation.

Budget accordingly. Beyond the insert itself (roughly $155 to $6,199 across our lineup), plan for the chimney liner, professional installation labor, and, for wood units, any needed chimney inspection or repair. These add-ons are exactly what buyers forget when they compare only sticker prices — and skipping the liner is not an option for a safe, efficient gas or wood install. Electric inserts avoid nearly all of this, which is why they're the lowest total-cost path to upgrading the look of a fireplace.

Maintenance by Fuel Type

Upkeep scales with fuel. Gas inserts are the lowest maintenance: keep the glass clean, have the unit and venting checked annually, and clear any debris from the burner. Wood inserts demand the most attention — remove ash regularly, burn only seasoned wood, and have the chimney and liner swept to remove creosote, ideally before each heating season. Electric inserts need little more than occasional dusting of the vents and an LED or bulb replacement over their long life. Regardless of fuel, an annual professional check on any vented insert keeps it safe and running at its rated efficiency.

Common Mistakes to Avoid

Three errors account for most insert regrets. Not measuring the firebox front and back — masonry openings taper, and an insert sized to the front width may not clear the narrower rear, so measure both. Forgetting the chimney liner in the budget — it's required for gas and wood, and it's a real line item, not an accessory. And oversizing or undersizing the heat output — an insert rated far above your room will overheat the space and run inefficiently, while an undersized one will disappoint as a heat source. Match the model's published heating-area range to your actual room, and when the insert is your primary heat, lean slightly larger.

Our Recommendation

For most homeowners upgrading an open fireplace: a direct-vent gas insert is the highest-value choice — 70–85% efficiency, instant controllable heat, and almost no upkeep. For authentic fire and serious heating where wood is available: an EPA-certified wood insert delivers real flame with modern efficiency and clean burning. For the simplest, lowest-cost retrofit: an electric insert adds flame ambiance and supplemental warmth with no venting and no gas work. Whichever fuel you choose, measure your firebox front-and-back before ordering, and budget for the chimney liner and professional installation on any gas or wood unit.

Browse Fireplace Inserts at Urban Supply

Explore the full fireplace insert collection — over 120 gas, wood, and electric models from Napoleon, Empire, Kingsman, Dimplex, and more. Comparing a full-fireplace build instead of a retrofit? See our gas fireplaces and wood-burning fireplaces, and complete your project with the right fireplace and wood-stove accessories. Orders over $299 ship free, and as authorized dealers our US-based team can help match an insert to your firebox dimensions before you order.

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