Converting a wood or gas fireplace to electric is straightforward when you know what to measure, what to plan for, and what to avoid. An electric insert slides into your existing masonry firebox without venting, gas fittings, or masonry work, no chimney liner, no contractor permits in most cases, and no combustion. What trips most homeowners up is not the installation itself but the decisions made before the insert arrives: wrong dimensions, skipped gas line steps, or no plan for the gap between the insert and the surround. This guide covers exactly what to check before you buy.

What Type of Electric Insert Actually Works for a Fireplace Conversion?

Two product formats work for fireplace conversions: a plug-in electric insert and a built-in electric unit designed for recessed installation. For most masonry fireplace conversions, a plug-in insert is the right starting point, it drops into the existing firebox opening, connects to a standard 120V outlet, and runs the flame effect with or without heat.

Built-in units are designed for new construction or framed wall cavities and generally require a dedicated circuit. They are not the right fit for a masonry firebox conversion unless significant framing work is already planned.

If you want the most realistic flame visual without combustion, Water Vapor Fireplace technology is worth understanding, these units produce a genuine three-dimensional flame effect using water mist and LED lighting. They require a controlled enclosure environment and are better suited to clients who want a true architectural focal point. For a standard masonry conversion, a high-quality electric insert with realistic flame technology covers most homeowners well.

How Do I Measure My Firebox Correctly Before Buying an Electric Insert?

Measure all three interior dimensions of your firebox, width, height, and depth, not just the width. This is the most common measurement mistake that leads to returns and reorders.

Here is how to measure correctly:

Width: Measure the interior opening at the widest point, from left masonry wall to right masonry wall. Measure at the front of the firebox, not the back, masonry fireboxes often taper toward the rear.

Height: Measure from the floor of the firebox to the underside of the lintel or throat above the opening. Do not measure the exterior surround opening, measure the actual interior cavity.

Depth: Measure from the front face of the firebox opening straight back to the rear wall. This is the dimension most homeowners skip, and it determines whether the insert body will physically fit without protruding.

The rule of thumb: your insert should be slightly smaller than the interior firebox opening on all three dimensions so it slides in cleanly. Trim kits and surrounds close the remaining gap at the face, that gap is expected and normal. What you cannot fix after the fact is an insert that is too wide, too tall, or too deep for the cavity.

Measure twice, write all three numbers down, and bring them when you are comparing products.

What Do I Need to Do With the Gas Line Before Installing an Electric Insert?

If you are converting a gas fireplace, the gas supply line must be addressed before the electric insert goes in. Do not simply leave the gas line capped inside the firebox and assume it is safe, this is one of the most common oversights in gas-to-electric conversions.

The correct sequence:

1. Have the gas supply to the fireplace shut off at the valve, typically a dedicated shutoff on the gas line feeding the unit.
2. The existing gas line should be properly capped or have the supply disconnected per local requirements. This is not electrical or masonry work, it is a gas fitting step, and local codes govern who can perform it.
3. Once the gas supply is confirmed off and the line is handled, the firebox is ready for the electric insert.

Electric inserts do not need a gas line. They also do not need the chimney or flue to remain open, the flue can be closed or sealed once the gas appliance is removed, since no combustion gases are produced. Confirm the firebox floor is clean and level before setting the insert.

Will the Electric Insert Look Built-In, or Will There Be Visible Gaps?

There will almost always be a gap between the insert face and the masonry surround, and that is not a problem, it is expected. The interior of a masonry firebox is almost never the same dimension as a manufactured insert, so a gap at the face is standard.

The solution is a trim kit or surround panel. Most quality electric inserts are sold with optional trim kits designed to bridge the gap between the insert face and the surrounding wall or mantel. These surrounds are typically available in multiple finishes and sizes and create a clean, built-in appearance once installed.

One customer who installed an electric insert into a 1906 dining room fireplace described the result: "This product worked perfectly and looks great! To finish we will still need to add tile, but other than that, the installation took just one weekend."

That detail about tile is worth noting: the trim kit handles the gap at the insert face, but if the original fireplace surround or hearth has exposed masonry or old tile, finishing that area is a separate cosmetic step that follows the insert installation. Plan for it, budget for it, and the result looks fully custom.

What Is the Step-by-Step Process for Converting a Fireplace to Electric?

The sequence matters more than most homeowners expect. Skipping steps or reversing the order is where most conversion problems originate.

Step 1, Measure the firebox interior (width, height, depth). Do this before you shop. Do not rely on the exterior surround dimensions.

Step 2, Select an insert sized to fit inside those measurements. Confirm the insert is smaller than the firebox on all three dimensions. Check the manufacturer's specifications for the trim kit coverage range.

Step 3, Handle the gas line (gas conversions only). Shut off the gas supply. Cap or disconnect the line per local requirements. Confirm the flue is closed or sealed.

Step 4, Clean the firebox. Remove ash, debris, and any old grate or gas components. The firebox floor should be clean and as level as possible.

Step 5, Confirm the electrical supply. Most electric inserts plug into a standard 120V outlet. Confirm there is an accessible outlet inside or immediately adjacent to the firebox, or plan for one to be added before the insert arrives.

Step 6, Slide the insert into the firebox. Most units are designed to drop in without fasteners. Some installations call for securing the insert to the surround, follow the manufacturer's installation guidelines.

Step 7, Install the trim kit or surround. This closes the gap at the face and creates the built-in appearance. Tile, stone, or other finish work on the surround is done after the insert is set.

Step 8, Test the unit. Run the flame effect first, without heat, to confirm the display is working. Then test the heater function separately.

What Are the Most Common Mistakes in a Fireplace-to-Electric Conversion?

The mistakes we see repeatedly are not about the product, they are about the decisions made before the product arrives.

Measuring only the width. Depth is the dimension that causes the most surprises. A masonry firebox that looks spacious from the front can be shallower than expected once you measure straight back.

Not planning for the trim gap. Homeowners who do not order a trim kit or surround end up with a visible gap around the insert face that looks unfinished.

Skipping the gas line step. Leaving an active or improperly capped gas line in a firebox that is now housing an electric appliance is a safety issue, not a cosmetic one.

Assuming any standard outlet will work. If the outlet inside or near the firebox is on a shared circuit that is already loaded, running the heater element can trip the breaker. Confirm the circuit before the unit arrives.

Ordering without reading the trim kit coverage range. Trim kits cover a specific gap range. If your firebox opening is significantly larger than the insert face, confirm the trim kit you are ordering will bridge that specific gap.

Conversion Readiness: How Do You Know You Are Ready to Buy?

A conversion is ready to move forward when four things are confirmed: you have all three interior firebox dimensions written down, the gas line situation is planned and scheduled (if applicable), you know where the electrical outlet is, and you have identified a trim kit that will cover the gap at your specific firebox opening.

That is the full picture. Homeowners who arrive at that point before they place an order almost never have installation problems. The ones who skip one of those steps, usually the depth measurement or the trim kit planning, are the ones who call after delivery with a problem that could have been caught in ten minutes of prep.

Electric Fireplaces Depot's product team works through exactly this checklist with customers before they order. If you are at the early stage of planning a conversion and want to spec this correctly, that guidance is available before you commit to a product.

Checklist

• Measure the firebox interior in all three dimensions, width, height, and depth, before comparing any electric insert products.
• For gas-to-electric conversions, schedule the gas shutoff and line cap before the insert arrives; do not leave this step until after delivery.
• Confirm a 120V outlet is accessible inside or immediately adjacent to the firebox; if not, plan for one before ordering.
• Identify the trim kit or surround that will cover the gap between your specific firebox opening and the insert face, check the coverage range against your measurements.
• If the original surround or hearth has exposed masonry or old tile, plan and budget for that finish work as a separate step after the insert is installed.
• Homeowners converting a wood or gas fireplace to an electric insert should run the flame-only mode first after installation to confirm the display before testing the heater function.

FAQ

Do I need to remove the old gas components before installing an electric insert? Yes. The existing gas logs, burner, and grate should be removed from the firebox before the electric insert goes in. More importantly, the gas supply line needs to be shut off and properly capped or disconnected per local requirements before the electric unit is installed. Do not leave an active gas supply line inside a firebox housing an electric appliance.

Can I run an electric fireplace insert without turning on the heat? Yes. Most electric inserts are designed to run the flame effect independently of the heater. This is useful year-round, you get the visual ambiance without adding heat to the room. The flame and the heater are typically controlled separately via remote or control panel.

How much smaller does the electric insert need to be than my firebox opening? The insert body should be smaller than the interior firebox dimensions on all three sides so it slides in cleanly without forcing. The exact clearance varies by product, but the trim kit is designed to bridge the remaining gap at the face. Check the manufacturer's specifications for both the insert dimensions and the trim kit coverage range before ordering.

Will I need to do anything to the chimney after converting to electric? Once the gas appliance or wood-burning components are removed and an electric insert is in place, the chimney flue is no longer needed for venting, electric inserts produce no combustion gases. The flue damper can be closed. If the chimney was previously used for a gas fireplace, confirm the gas supply is properly shut off and the line is handled before sealing anything.

What if my firebox opening is an unusual size, can I still find an electric insert that fits? Most masonry fireboxes fall within the size range covered by standard electric insert product lines, but the depth is the dimension most likely to cause a mismatch. If your firebox is unusually shallow, confirm the insert depth against your measurement before ordering. Electric Fireplaces Depot's product team can help match your specific measurements to the right unit and trim kit.

Do electric fireplace inserts require any special wiring or a dedicated circuit? Most plug-in electric inserts run on a standard 120V household outlet. If the insert uses a heater element drawing close to the circuit's capacity, a loaded shared circuit can trip the breaker. For higher-output units or built-in installations, a dedicated circuit may be required, check the manufacturer's electrical specifications for the specific unit before installation.

How long does a fireplace-to-electric conversion typically take? For a straightforward masonry firebox conversion with an accessible outlet and no gas line complications, most installations are completed in a single weekend. Tile or surround finish work, if needed, adds time depending on the scope of the cosmetic update.

If you are planning a conversion and want to make sure you get the sizing, trim kit, and installation sequence right before you order, the team at Electric Fireplaces Depot is available to work through it with you. Call or text 800-309-2144 or email sales@oloctricfireplacesdepot.shop, bring your three firebox measurements and we will spec this correctly from the start.