How to Install Electric Fireplace Insert: Step-by-Step Guide

Converting an old wood-burning firebox to electric is one of the easiest ways to get the look of a fire without smoke, ash, or chimney sweeps. Learning how to install electric fireplace insert units is mostly about three things: measuring accurately, preparing the old firebox safely, and getting power to the unit in a code-compliant way. Most plug-in models can be installed by a handy homeowner in two to four hours. Hardwired models and anything involving a new circuit are a different story, and this guide explains where that line falls.

How to Install Electric Fireplace Insert Units: Planning First

Before buying anything, confirm that an insert is the right product. An electric insert is a boxed firebox designed to slide into an existing masonry or prefabricated fireplace opening, with a surround or trim kit covering the gap. That differs from wall-mounted linear units that recess into a framed wall and from freestanding electric stoves. If you have no existing opening, you are shopping for a different product.

Next, decide how the unit will get power. Most inserts plug into a standard 120-volt outlet and draw about 1,500 watts, or around 12.5 amps, with the heater running. That is a substantial load, so the manufacturer will typically specify a dedicated or lightly loaded 15- or 20-amp circuit. Some larger units offer optional hardwiring, and a few require 240 volts. Read the installation manual for your specific model before you start; it overrides any general advice.

Tools and Materials

• Tape measure, level, and a notepad for measurements
• Shop vacuum, stiff brush, and dust mask (N95 or better)
• Flashlight and safety glasses
• Screwdrivers and a drill/driver
• Chimney balloon, insulated damper plug, or sheet-metal block-off (to stop drafts)
• Trim kit or surround sized for your opening
• Non-contact voltage tester
• Helper for lifting (many inserts weigh 50 to 100 lb)

Step 1: Measure the Firebox Opening

Accurate measurements determine everything else. Measure at several points because older masonry fireboxes are rarely square:

1. Front width: measure across the opening at the top, middle, and bottom; use the smallest number.
2. Front height: measure left, center, and right; use the smallest.
3. Rear width: many fireboxes taper toward the back, so measure the back wall separately.
4. Depth: measure from the front edge of the opening to the back wall at the insert’s intended height.
5. Hearth and surround: note the distance to the mantel, any protruding brick, and the location of the nearest outlet.

Compare your numbers with the manufacturer’s minimum opening dimensions. Insert widths commonly fall between about 23 and 36 inches, and the trim kit usually adds 2 to 6 inches on each side to hide gaps. Choose a unit that fits the smallest dimension, not the largest.

Step 2: Prepare the Old Fireplace

Clean the firebox thoroughly. Remove the grate, andirons, and any ash, then vacuum with a shop vac fitted with a fine-dust filter. Brush loose soot from the walls. Creosote and soot are irritants, so wear a mask and eye protection.

Next, address the chimney. An electric insert needs no venting, but an open flue will pull warm room air up the chimney all winter. Close the damper and add a chimney balloon or insulated block-off plate. If the damper is rusted or missing, a top-sealing damper installed at the crown or a sheet-metal block-off is a permanent fix.

This is also the moment to inspect the structure. Look for cracked firebrick, loose mortar joints, water stains, or signs of animals nesting. Even if you will never burn wood again, a leaking chimney crown or crumbling masonry can let water into walls. Have a certified chimney sweep inspect it if you see damage, and if any gas line serves the fireplace (for an old gas log set), a licensed gas fitter or plumber must cap it properly before you proceed. Never simply leave a gas valve closed behind an electric unit.

Step 3: Plan the Electrical Connection

This step decides whether the job stays DIY. Options include:

• Existing outlet next to the fireplace: the simplest route; route the cord neatly around the surround. Do not use extension cords or power strips.
• Outlet inside the firebox: many installers add a receptacle inside the opening so the cord is hidden. This requires running new wiring through or beside masonry.
• Hardwired connection: the unit connects directly to a circuit via a junction box, per the manual.

When to call a licensed electrician: any new outlet, new circuit, hardwiring, 240-volt unit, or work in the main panel should be done by a licensed electrician, with a permit where your jurisdiction requires one. An electrician can also confirm that the circuit is not already shared with other heavy loads such as space heaters or a microwave, which is a common cause of tripped breakers. Before touching any existing wiring yourself, shut off the breaker and confirm with a non-contact tester.

Step 4: Assemble the Trim Kit

Most inserts ship with a separate trim or surround kit. Attach it to the insert body on the floor before sliding the unit in, following the manual’s screw locations. Some kits have adjustable side panels; set them loosely so you can fine-tune the fit later. Protect the glass front with the cardboard packaging while you work.

Step 5: Set the Insert in Place

1. Lay a moving blanket on the hearth to protect tile or stone.
2. Feed the power cord through the intended path before pushing the unit fully in. Many models let you route the cord out the side or back.
3. Slide the insert in with a helper, keeping it level. Do not pinch the cord between the insert and masonry.
4. Level and shim with plastic or composite shims if the firebox floor is uneven.
5. Snug the trim against the masonry so it covers all gaps. Secure it per the manual, usually with brackets or tension screws; some units rely on the trim fit alone.

Leave the air intake and heater outlet completely unobstructed. Most inserts pull room air in at the bottom or sides and blow heated air out at the top or front. Blocking these vents can overheat the unit and trigger its thermal cutoff.

Step 6: Connect, Test, and Adjust

Plug in or have your electrician complete the hardwired connection, then restore power. Test each function: flame effect, brightness, color settings, the heater at low and high, the thermostat, and the remote. Run the heater on high for 30 minutes and check that the breaker holds, the cord and plug stay cool to the touch, and there is no burning smell beyond a brief new-appliance odor. If the plug or outlet gets warm, stop using the unit and have the circuit checked.

Finally, adjust the flame settings to taste. Many homeowners run the flame effect year-round without heat, which uses only a small amount of electricity, often under 100 watts on LED models.

Costs and Timeline

• Insert unit: about $300 to $1,500, with premium realistic-flame models costing more.
• Trim kit (if sold separately): about $50 to $250.
• Chimney balloon or block-off: about $50 to $150.
• Electrician to add an outlet or dedicated circuit: roughly $200 to $800, depending on distance to the panel and masonry work.
• Professional full installation: commonly $200 to $600 in labor beyond electrical work.

A plug-in installation takes a few hours. Budget a day or two if you are scheduling an electrician or chimney inspection first.

Common Mistakes to Avoid

• Buying before measuring. A unit that is a half inch too wide will not go in.
• Leaving the flue open. Heat loss up the chimney can cancel out much of what the insert produces.
• Using an extension cord. Manufacturers prohibit it because of the continuous high current draw.
• Ignoring an old gas line. Any gas supply must be professionally capped.
• Covering vents with decor. Keep stockings, candles, and plants away from the heater outlet.

Once you know how to install electric fireplace insert units correctly, the process is predictable: measure carefully, seal the chimney, sort out power the safe way, and let the trim kit handle the finishing. Done right, the fireplace becomes the easiest heat source in the house to maintain.