How Does a Fireplace Insert Work to Heat a Room?

How does an insert stop cold drafts and heat loss?

A traditional open masonry fireplace feels cozy, but it is one of the most inefficient heating setups in any home. When you light a fire in an open hearth, the chimney pulls warm room air out of your living space. An open fireplace often sends more heated air up the flue than it radiates into the room. Once the fire dies down, that open chimney flue behaves like an open window in winter. Freezing outdoor air sinks into the hearth while furnace warmth escapes straight up the stack.

A fireplace insert solves this problem by turning an open cavity into a sealed heating system. The insert is a self-contained metal firebox (an inner fire chamber built from heavy steel or cast iron) that slides directly into your existing opening. Once in place, the insert creates a solid barrier between your living space and the cold chimney flue.

To stop drafts completely, you close the old flue or install a top-sealing damper. Learning how to close a fireplace damper ensures you block outside air from entering behind your unit. You also place thick fiberglass insulation strips around the perimeter of the casing. This stops cold air from leaking around the edges of the box, sealing your room off from drafts.

How does an insert push warmth into your room?

Traditional fireplaces radiate heat only from the face of the flames. When a wood fire burns, you feel warm only right in front of the hearth, while the rest of the room stays chilly. An insert changes this by moving air through built-in circulation chambers.

The unit draws cool air in from the floor through small intake slots along the bottom or sides of the frame. Inside, this air travels through a sealed passageway wrapping around the heated core. As the air passes over hot metal walls or electric elements, it absorbs thermal energy.

Next, a convection blower (a quiet internal fan that circulates warm air) pushes heated air out through a top heating vent or blower grille. This creates a gentle circular airflow across your room. Cool air enters the bottom, warms inside, and flows back out into the room.

The exact heating method depends on the design:

• Basic fan-forced coil heaters use an electric resistance wire paired with a blower fan. Cool air blows across the glowing wire coil and exits into the room. These work well for supplemental zone heating in spaces up to 400 square feet, letting you lower your main furnace thermostat.
• Infrared quartz heaters use special quartz tubes producing infrared light waves. Rather than just heating the air, infrared quartz warms people, floors, and furniture directly. This heat keeps natural room humidity so air does not feel dry, and warms spaces up to 1,000 square feet. If you have an open floor plan, choosing a firebox insert designed for large rooms provides that extra reach.

What is the difference between electric, gas, and wood inserts?

While all inserts fit inside an existing hearth opening, they generate and deliver heat through very different power sources.

Wood-burning inserts suit homeowners who want real logs and high heat output. These feature an airtight door with heat-resistant glass and a secondary burn system that burns wood smoke before it enters the flue. However, they require a full-length, flexible stainless steel chimney liner to the chimney cap. You also need to clean ash, store firewood, and schedule chimney sweeps.

Gas inserts burn natural gas or liquid propane across ceramic logs. They provide instant heat with the flip of a switch or remote control. Most use a sealed direct-vent system that pulls outdoor combustion air through one pipe inside your chimney and vents exhaust through a second pipe. Gas inserts deliver steady warmth, but require professional gas line installation and proper venting to prevent carbon monoxide risks.

Electric inserts offer the simplest setup because they require no fire, no gas lines, and no venting pipes. An electric firebox insert simply plugs into a standard 120-volt wall outlet. An internal heating element produces between 4,600 and 5,200 BTUs (a standard heat output measurement) on its maximum setting. Most models operate on two levels: a 750-watt low setting and a 1,500-watt high setting. Because there is no combustion, an electric unit is completely efficient, converting every watt of power directly into supplemental room warmth.

How do you measure, fit, and seal the opening?

Installing an insert begins with accurate measurements of your existing fireplace opening. If an insert is even a half-inch too large, it will not slide in. If it is too small, you will see wide gaps around the frame.

Grab a tape measure and record these key dimensions:

• Measure opening width at both the front and the back wall. Many brick fireboxes taper inward toward the rear, making the back narrower than the front.
• Measure opening height from the hearth floor to the lowest point of the top lintel (the horizontal support bar across the top opening). Measure at the left, center, and right.
• Measure usable depth from the front brick face to the back wall.

Once you have your dimensions, pick a unit that fits comfortably inside those limits. Most manufacturers offer a trim kit (an outer metal frame that covers gaps between the insert and the brickwork). This metal surround overlaps the exterior brick face, hiding leftover space around the insert for a clean look.

Before sliding the unit in, apply an adhesive fiberglass insulation strip along the back edge of the trim kit or around the insert perimeter to block stray drafts.

Safety is essential when connecting power. An electric insert drawing 1,500 watts pulls roughly 12.5 amps. Because a standard household circuit handles 15 amps, plug the unit into a dedicated circuit (an outlet that does not share its breaker with other power-hungry appliances like microwaves or hair dryers). Always plug the heavy three-prong plug directly into a wall receptacle. Never use an extension cord or power strip, as continuous heavy current can overheat thin wires and cause a fire hazard. Keep all blankets, curtains, upholstery, and area rugs at least 3 feet (36 inches) away from the front heating vent.

Can you enjoy the flames without running the heater?

One major advantage of an electric fireplace insert is the ability to separate the flame display from the heater function. Traditional wood and gas fires always produce intense heat whenever they burn, making them unusable during warm spring and summer evenings.

Electric models feature an independent flame-only mode. In this mode, the internal heating coil and blower fan stay shut off, while the flame display continues to run. You get the comforting glow of a hearth fire without adding warmth to the room.

The flame effect relies on simple, clever engineering. Behind a decorative log set or glass crystal bed, energy-efficient LED lights shine onto a spinning metal rod with reflective ribbons or mirror-like facets. As a small internal motor spins the rod, it reflects moving light onto a frosted rear screen. This creates the illusion of dancing, rolling flames.

Because the LED lights and small motor draw very little power, running the flame-only mode costs just pennies per day. When chilly weather arrives, you press a button on your remote control to switch on the 1,500-watt heating element. If you want a stylish unit that balances attractive flame patterns with steady heat output, looking into a well-built electric fireplace gives you the right mix of visuals and durability.

What should you look for before buying an insert?

If you are ready to update a drafty hearth or an empty opening, choosing the right kind of fireplace insert comes down to how much work you want to do and how you plan to heat the space.

If your old masonry fireplace has an intact chimney and you want high-output heating for severe winter weather, a sealed wood or direct-vent gas insert is an effective choice. However, keep in mind that these require professional flue installation, fuel lines, and ongoing maintenance to stay safe.

If you want quick supplemental heat, zero venting hassles, and total control over your room ambiance, a plug-in electric insert or an electric log set is the easiest solution. A full firebox insert gives you a finished, glass-fronted unit that fills the opening, while an electric log set sits right on your existing fireplace grate and projects realistic flames against your existing brick back wall.

Before making a choice, double-check your electrical setup. Make sure you have a wall outlet close enough that the power cord reaches without straining, and confirm that the circuit breaker can support a 1,500-watt draw without overloading. Check the location of the heat exhaust as well. If you plan to mount a television above the mantel, select a unit with a front-facing or bottom-facing heat vent, and maintain at least 8 to 12 inches of clearance between the top of the fireplace and your electronics.

1

ORALNER 26" Electric Fireplace Insert Log Set, Infrared Quartz Heater

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  9.8
• Brand
  ORALNER

Key specs2

Heating Coverage

Up to 1,000 sq ft (5,120 BTU)

Log Set Firebox Fit

At 26 inches wide and 8.8 inches deep, this open log set sits directly on an existing fireplace floor and reflects simulated flames onto your rear brickwork without a full metal enclosure.

Pros & cons42

Pros

• Quartz infrared heating produces 5,120 BTU to provide supplemental warmth up to 1,000 square feet
• Flame visuals and heating element operate independently with five adjustable brightness settings
• Slim 8.8-inch depth easily slides into shallow masonry hearth openings
• Automatic overheat protection and an 8-hour sleep timer prevent continuous unattended operation

Cons

• Flame visuals rely on projecting onto the back wall of an existing firebox rather than an enclosed screen
• Listing does not state an adjustable thermostat temperature range in degrees

2

Oxhark Flame 33 Inches Electric Fireplace Insert with Trim Kit,

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  9.2
• Brand
  Oxhark Flame

Key specs2

Trim Kit Dimensions

41.34 in W x 24.4 in H x 7.87 in D

Temperature Control Range

The built-in digital thermostat adjusts between 62 and 99 degrees Fahrenheit (17 to 37 Celsius) using either the front touch screen or remote control.

Pros & cons42

Pros

• Included trim kit expands exterior dimensions to 41.34 inches wide to cover hearth opening gaps
• Dual wattage modes at 750W and 1500W let you balance power draw against heating needs up to 400 square feet
• Digital thermostat provides precise temperature regulation between 62 and 99 degrees Fahrenheit
• Offers eight flame colors and six brightness levels that operate with or without heat

Cons

• Overall depth of nearly eight inches requires verifying masonry cavity or stud cutout clearance
• Heater shuts off automatically only after reaching a high thermal threshold of 212 degrees Fahrenheit

3

Oxhark Flame 36 Inches Electric Fireplace Insert with Trim Kit,

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  9.2
• Brand
  Oxhark Flame

Key specs2

Opening Coverage

Covers openings up to 43.89 inches wide

Installation Options

• Recessed into existing fireplace masonry or custom framing
• Wall mounted using the supplied wall bracket hardware
• Includes metal trim surround to conceal framing perimeter gaps

Pros & cons42

Pros

• Wide 43.89-inch outer trim kit provides a clean finished look across broader masonry openings
• Two heat settings at 750W and 1500W warm spaces up to 400 square feet
• Customizable flame display includes eight color choices and six brightness steps with heatless operation
• Comes with both a multi-function remote control and a built-in touch screen interface

Cons

• Heavier profile demands secure wall mounting or level hearth placement before framing
• Power cord length is limited to 6 feet, necessitating an outlet near the firebox without extension cords

4

Electric Fireplace Logs 20-Inch, Remote Controller Fireplace Insert Log Heater,

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  8.8
• Brand
  Riseon

Key specs2

Operating Noise Level

40 dB or lower

Quartz Tube Heat Delivery

Unlike basic air-blowing coils, the 1500W quartz tube emits infrared warmth that radiates directly toward room occupants while keeping blower noise at or below 40 dB.

Pros & cons42

Pros

• Infrared quartz heating tube warms people directly using 1500W of power
• Requires zero framing or mounting hardware by sliding directly into an existing fireplace opening
• Quiet internal blower runs at 40 decibels or lower to minimize background hum
• Resin log display provides five flame colors and five flame speeds that work with or without heat

Cons

• Compact 20-inch width may look undersized inside wide traditional masonry hearths
• Listing does not state numerical heating square footage coverage

5

COSTWAY 28.5-Inch Electric Fireplace Inserts, 750W/1500W Wall Recessed and Freestanding

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  8.8
• Brand
  COSTWAY

Key specs3

Safety Certification

ETL certified

Compact Chassis Fit

6.0 in depth for slim hearth cavities

Thermostat Range

62°F to 82°F (0 to 8-hour timer)

Pros & cons42

Pros

• Shallow 6-inch chassis depth fits easily into tight fireplace cutouts and shallow wall cavities
• ETL safety certification confirms verified compliance with indoor electrical standards
• Adjustable thermostat maintains target room temperatures between 62 and 82 degrees Fahrenheit
• Provides two energy settings at 750W and 1500W with coverage up to 400 square feet

Cons

• Flame customization is limited to three color modes compared to eight on similar insert models
• Narrower upper thermostat limit of 82 degrees Fahrenheit restricts maximum heat output preference

6

Rodalflame Fireplace Insert Trim Kit for 32.99" W x 24.92"

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  8.8
• Brand
  RODALFLAME

Key specs2

Inner Cutout Dimensions

30.3 in W x 23.6 in H

Hearth Gap Concealment

This sheet metal surround measures 41.9 inches wide by 29.5 inches high to seal off open perimeter margins around matching 33-inch electric fireboxes.

Pros & cons32

Pros

• Heavy-duty sheet metal frame conceals unsightly gaps between hearth openings and insert bodies
• Slim 0.7-inch profile sits flush against the outer wall or fireplace surround
• Includes all necessary assembly hardware for rapid installation

Cons

• Inner opening dimensions of 30.3 by 23.6 inches are only compatible with specific size-matched fireboxes
• Does not generate heat or include electrical components on its own

7

Riseon Electric Fireplace Logs Inserts Heater 23-Inch, Remote Controller Fireplace

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  8.8
• Brand
  Riseon

Key specs2

Acoustic Rating

40 dB or lower

Standalone Grate Design

Engineered as a plug-in replacement for wood grates, this resin log set provides instant infrared radiant heat and independent flame effects without requiring venting or wall modification.

Pros & cons42

Pros

• Features 1500W infrared quartz heating to project supplemental radiant warmth into the living area
• Includes five flame colors and five speed settings on realistic resin logs for customized ambiance
• Acoustic dampening keeps blower sound levels at or under 40 decibels during heater operation
• Standalone log grate design plugs into any standard 120V grounded outlet without masonry remodeling

Cons

• Listed 20-inch base footprint differs from the 23-inch model title, requiring careful hearth measurement
• Product details do not state a specific square footage heating rating

8

Rutland Products 1111 Fireplace Insert Insulation Fiberglass, 1-1/2-Inch by 10-Feet,

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  8.6
• Brand
  RUTLAND PRODUCTS

Key specs2

Thermal Rating Limit

Up to 225°F

Draft Barrier Role

Applied between the metal insert flange and outer brickwork, this 1.5-inch adhesive fiberglass gasket stops cold chimney drafts and keeps blower-circulated room air from escaping.

Pros & cons42

Pros

• Self-adhesive backing allows simple strip application along insert flange perimeters
• Dense fiberglass construction blocks room drafts and seals air gaps against rough masonry
• Rated for thermal resistance up to 225 degrees Fahrenheit
• Ten-foot continuous roll provides ample length to border standard fireplace insert perimeters

Cons

• Must be replaced each time an insert is pulled out for maintenance or chimney sweeping
• Thermal ceiling of 225 degrees Fahrenheit is not intended for direct contact with active wood flame zones

Last update on 2026-10-02 / Affiliate links / Images, Product Titles, and Product Highlights from Amazon Product Advertising API

FAQs

Do you need a chimney to run an electric insert?

No, an electric fireplace insert does not produce smoke, exhaust, or carbon monoxide, so it requires no chimney or venting pipes. You can place one inside an old masonry fireplace with the damper closed, or mount it inside an entertainment center or framed wall opening. All it requires to function is a standard three-prong wall outlet.

Can an electric insert heat an entire house?

No, an electric insert is designed for supplemental zone heating, not as a primary heat source for a whole home. With a maximum heat output between 4,600 and 5,200 BTUs, an insert warms the specific room you are spending time in, which allows you to turn down your central thermostat and lower your heating bills.

Is the front glass safe for children and pets?

Yes, the front viewing glass on most electric inserts stays cool to the touch because the heating element is separated from the display screen. However, you must always be mindful of the metal heating vent or blower grille where the hot air blows out, as that specific metal trim can get quite hot during operation.

Why did the heater suddenly stop blowing warm air?

The most common cause is a tripped overheat safety shutoff, which cuts power to the heater if dust blocks the intake vents or if airflow is restricted. To reset the unit, unplug the power cord from the wall outlet, check and clear any lint or pet hair from the intake vents, wait 10 to 15 minutes, and plug it back in. Also check your thermostat setting to confirm it is set higher than the current room temperature.