How-to · masonry openings

How to install an electric fireplace insert

Eight steps for fitting an insert into a firebox you already have. The electrical step is marked, because that is the one where amateur work becomes a fire risk rather than a mistake.

By Scooter M.Published September 2, 2026Last reviewed September 2, 2026

Hands using tools during a home improvement project

Before anything else

Fitting an electric insert into an existing masonry firebox is a plug-in job: measure the opening, confirm power, place the unit, fit trim. There is no venting, no gas and no chimney work. The only part that is not DIY is adding a receptacle, and that is a licensed electrician's job in most jurisdictions.

What you need

A tape measure and something to write four numbers on
A flashlight — masonry openings are dark and you need to see the back
A vacuum, for the ash and soot that is definitely still in there
The insert's own manual, which supersedes anything on this page
A trim kit, if the opening is wider than the unit

The eight steps

Measure four dimensions. Front width, rear width, height, depth. Masonry openings taper — the rear width is the constraint, and it is the measurement people skip.
Confirm the flue is closed and the firebox is done with. An open damper above an electric insert pulls conditioned air out of the room all winter. Close it, or cap the chimney if you are finished with it permanently.
Clean the firebox properly. Vacuum out ash, soot and debris. Anything left in there will end up circulating when the fan runs, and old creosote smells when it warms.
Find the power before you buy anything. Identify the nearest receptacle and what else is on that circuit. At 1,500 W the insert draws about 12.5 amps continuously, most of a 15-amp circuit on its own.
STOP HERE if there is no receptacle in reach. Adding one inside a firebox means new wiring, and depending on where you live it means a permit and an inspection. This is a licensed electrician's job. Do not run the unit from an extension cord or a power strip — manufacturers prohibit it and the load is exactly why.
Dry-fit the unit before committing. Slide it in without plugging it in and check it clears the rear taper, sits level and does not rock. This is when you find out whether the rear measurement was right.
Connect and test on low first. Plug in, run the flame alone, then the 750 W setting, then 1,500 W. Listen for fan noise against the masonry and check nothing rattles. Confirm the breaker holds under the full load for at least fifteen minutes.
Fit the trim, and check the reveal from where you sit. Trim looks different at standing height than from a sofa. Stand back, sit down, and adjust before you fix anything permanently.

What running it will cost you afterward

What a 1,500 watt electric fireplace costs to run at 18.34 cents per kilowatt-hour
Usage	Hours	Heat on (1,500 W)	Flame only (~100 W)
One evening	4	$1.10	$0.07
A week of evenings	28	$7.70	$0.51
A month, 4 hrs a night	120	$33.01	$2.20
A 90-day winter, 4 hrs a night	360	$99.04	$6.60
Per hour	1	27.5¢	1.8¢

Once it is in, at the 1,500 W setting. Computed as (watts ÷ 1000) × rate, at 18.34¢/kWh — the US residential average from EIA Electric Power Monthly, Table 5.3 (June 2026), released 2026-08-26. Your rate is on your own bill — put it into the calculator. The flame-only column assumes a conservative 100 W for the LED assembly with the heater switched off.

Worth knowing at install time, because it changes how you use the unit. Most owners settle into flame-only for the great majority of hours and the heater for genuinely cold evenings — which, at under two cents an hour against 27.5, is a rational habit rather than a frugal one.

Common mistakes

Mistake	What happens	Fix
Measuring only the front	The unit fouls the rear taper and will not seat	Measure the back. Always
Forgetting the trim kit	A visible gap around a unit narrower than the opening	Order it with the unit, not after
Extension cord or power strip	Continuous 12.5 A load on a cord not rated for it	Wall receptacle only, no exceptions
Leaving the damper open	Heated room air goes up the chimney all winter	Close the damper or cap the flue
Not vacuuming first	Soot smell and circulating debris when the fan runs	Vacuum thoroughly before dry-fitting

Questions people actually ask

Can I install an electric fireplace insert myself?

The physical fit, yes — it is a measure, clean, place and plug-in job with no venting or gas involved. Adding a receptacle where there is not one is the exception and should go to a licensed electrician.

Do I need to close the damper?

Yes. The insert vents nothing, so the flue serves no purpose, and an open damper draws heated room air up the chimney continuously. Close it, or cap the chimney if the fireplace is permanently retired.

How do I hide the power cord?

The tidy answer is a receptacle inside the firebox, added by an electrician. Short of that, run the cord along the hearth joint where the mortar line hides it, or use a floor outlet if one is close. Do not route it under a rug — that is a known ignition risk with high-draw appliances.

Does the insert need clearance around it?

Follow the manual, which will state the manufacturer's own figures. Generally the concern is airflow at the heater outlet rather than combustible clearance, since there is no combustion — but the manual supersedes any general rule, including this page.

Sources

Every figure on this page is either taken from one of these documents or computed from a formula shown on the page. Nothing here is recalled from memory.