Modern Flames Redstone vs. Spectrum Slimline: Which Built-In Is Right for You?

Last reviewed: October 1, 2026

Modern Flames Redstone and Spectrum Slimline suit different fireplace shapes and installation plans. Start with the existing opening, the desired proportions, and the required electrical connection.

The short answer

Choose the Redstone if you have an existing fireplace opening to fill or want a traditional, taller fireplace shape. Choose the Spectrum Slimline if you want a wide, modern linear fireplace on a wall that has no opening in it. Compare linear and traditional electric fireplaces when the choice is between a wide display and a more conventional firebox shape.

That is the whole decision in one sentence. Everything below explains why.

Redstone Built-In Series

The Redstone Built-In Series offers a traditional firebox shape in nominal 26, 30, 36, 42, and 54-inch sizes. It supports compatible existing-fireplace inserts and custom built-in installations, with different electrical instructions for those two methods.

Three practical details set it apart from the rest of the Modern Flames catalog:

• Electrical work depends on the installation. The Redstone owner's manual, installation sections, specifies plug-in power for an insert and hardwiring for a built-in installation. A qualified electrician must handle the prescribed electrical work; a plug does not establish that an existing outlet is suitable.
• Depth varies by model. The manual's finished-opening table specifies 10 inches for RS-2621 through RS-4229 and 12 inches for RS-5435. Confirm the width, height, and finish details in the same drawing.
• Plan the whole conversion. Check the existing opening and the selected trim before ordering. Arrange any necessary electrical or existing-fuel-system work with the appropriate qualified trade.

The Redstone uses Hybrid-FX flame effects with separately adjustable visual settings. Its manufacturer-rated 5,000 BTU heater supplies supplemental heat; actual room performance depends on the space and its heat loss.

Good fit if: you want a traditional fireplace shape and have a compatible existing opening or a planned built-in enclosure.

Spectrum Slimline Series

The Spectrum Slimline Series is a linear fireplace in 50, 60, 74, and 100 inches. It is the entry point into the wide, modern format that Landscape Pro and Orion occupy at higher price levels, in a shallower cabinet. The Modern Flames buying guide provides the broader series comparison if this model does not fit the project.

The Allwood Wall System is a pre-finished package that includes the 60-inch Spectrum Slimline, with Weathered Walnut, Coastal Sand, and Driftwood Gray finish options in the current catalog. Do not assume the package fits every Spectrum size. Wall support, electrical access, and the TV-mounting plan still need checking.

Good fit if: you want a wide linear fireplace and can provide suitable wall support and electrical access, using a recessed, surface-mounted, or compatible surround installation.

Comparing the two directly

Format and proportion

Redstone is taller and narrower, reading as a conventional fireplace. Spectrum is wide and short, reading as a modern linear feature. This is an aesthetic decision more than a technical one, and it is usually settled by the room rather than the budget.

Installation

Redstone supports insert and built-in installations. Spectrum supports wall-mounted, recessed, and mantel installations, so it does not always require a new wall opening. Follow the Spectrum Slimline owner's manual, Installation and Assembly section, for the chosen mounting method.

Size range

Redstone runs 26 to 54 inches. Spectrum runs 50 to 100 inches. They only overlap around the 50-inch mark, so in practice the size you need often makes the decision for you.

Finishing

Redstone includes trim kits for a clean edge against an existing opening. Spectrum can be paired with the Allwood Wall System for a complete pre-finished presentation.

Common mistakes

Choosing by nominal width alone. Compare firebox shape, actual cabinet dimensions, and the intended installation method. Our comparison of electric inserts and wood-burning inserts explains the wider conversion decision.

Measuring only the front of the opening. Record front and rear widths, height, depth, and obstructions, then compare the complete space with the selected model's drawing.

Assuming these are stripped-down versions of Orion. They are different formats built for different projects. Our Orion vs. Landscape Pro comparison covers the premium end of the lineup.

Frequently asked questions

Can the Modern Flames Redstone fit into an existing wood-burning fireplace?

It can fit a compatible existing opening. Confirm all opening dimensions and follow the insert-installation instructions, including the electrical requirements, before ordering.

Does the Redstone need to be hardwired?

The manual specifies hardwiring for a built-in installation and plug-in power for an insert installation. Follow the instructions for the chosen method; do not assume every Redstone installation is plug-in.

How much wall depth does the Redstone need?

The finished-opening depth is 10 inches for RS-2621 through RS-4229 and 12 inches for RS-5435 in the cited manual. Use the full model-specific drawing before construction.

What sizes do these two series come in?

The Redstone comes in 26, 30, 36, 42, and 54 inches. The Spectrum Slimline comes in 50, 60, 74, and 100 inches.

Can I get the Spectrum Slimline with a finished surround?

The current Allwood package includes the 60-inch Spectrum Slimline and offers Weathered Walnut, Coastal Sand, and Driftwood Gray finishes. Check package dimensions, support, and electrical access before ordering.

Final thought

Compare the electric fireplace inserts collection for a traditional opening and the wall-mounted electric fireplaces collection for surface-mounted alternatives. The right choice depends on the room, the mounting method, and the electrical plan.