A wood-burning fireplace looks great until you are the one hauling logs, sweeping ash, and watching most of your heat disappear up an open chimney. Converting it to gas with a direct vent insert fixes all three — instant, controllable heat at the flip of a switch, no mess, and far better efficiency.
The whole project hinges on one thing: the dimensions of your existing firebox opening. Get that measurement right and the rest is straightforward. Get it wrong and nothing fits. Verified minimum openings for every Kingsman IDV insert are below.
Minimum fireplace opening by model
| Insert | Minimum opening (W x H x D) | Input max (NG / LP) | Viewing area |
|---|---|---|---|
| IDV24 | 24 1/4" x 18 1/2" x 14" | 24,000 / 24,000 BTU | 20 13/16" x 11" |
| IDV26 | 28–33" x 19 1/2" x 14 1/8" | 30,000 / 30,000 BTU | varies by front |
| IDV34 (CV1 front) | 28 5/8" x 21 1/2" x 17 3/4" | 31,000 / 28,500 BTU | 25 5/8" x 14 1/8" |
| IDV34 (CV6 front) | 26 1/4" x 21 3/8" x 15 3/4" | 31,000 / 28,500 BTU | 25 5/8" x 14 1/8" |
| IDV44 | 32 7/8" x 25 3/4" x 18" | 34,250 / 30,000 BTU | 29 7/8" x 18 3/8" |
Specifications per the Kingsman Fireplaces United States Price List, effective March 1, 2026. Measure your opening at its narrowest point — masonry fireboxes often taper toward the back.
Two things worth noticing in that table. The IDV26 accepts a range of openings depending on whether its Clean View front components are installed in or out, which makes it unusually forgiving. And the IDV34 has two front options with different depth requirements — if your firebox is shallow, the CV6 front needs two fewer inches of depth than the CV1.
What converting to gas actually means
A gas fireplace insert is a sealed gas firebox that slides into your existing fireplace opening and reuses the chimney chase to run its venting. You keep your existing structure and mantel; the insert transforms how it works. If you do not have an existing masonry fireplace and are building from scratch, you want a zero-clearance unit instead — our zero-clearance vs. insert guide explains the difference.
How a direct vent insert works
Kingsman IDV inserts use direct venting with sealed combustion: a co-axial pipe draws combustion air from outside and exhausts outside, completely separated from your room air. That is the efficiency win over an open wood fire. Instead of pulling heated room air up the chimney, the insert keeps it inside and radiates warmth back through ceramic glass and a heat-activated, variable-speed blower.
Efficiency figures reflect this: the IDV34 runs roughly 63–65% fireplace efficiency and the IDV26 roughly 65–67% — well above the mid-50s of several larger built-in units.
What you need for a complete, working unit
A Kingsman insert is configured from parts that must be ordered together. Missing one holds up the whole install:
- The insert — the sealed firebox, in your chosen fuel and ignition
- A Clean View front — required on every unit, not optional
- Media — a fiber split oak log set, or a glass support platform with bronze decorative glass
- A surround — fills the gap between the insert and your existing opening; sizes vary, and a riser is available if you need 2 1/2" more coverage height
- A liner — refractory brick or porcelain reflective, optional but changes the look considerably
- Venting — Kingsman flex venting and termination only on the IDV line, plus a gas supply line
That last point matters: Kingsman specifies its own flex venting and termination components for IDV inserts. Third-party venting is not an option here.
Choosing your size
Measure first, then match output to the room second. Most rooms need less heat than people assume, so opening dimensions usually decide the model for you. The IDV24 fits the smallest openings; the IDV26 suits mid-size openings with flexible front options; the IDV34 handles mid-to-large; and the IDV44 is the largest and highest-output at 34,250 BTU.
Worth knowing: the IDV44 produces nearly as much heat as the 60-inch ZCVRB60 linear (35,000 BTU) at roughly half the price and with no new framing. If you have the opening for it, an insert is the best heat-per-dollar in the Kingsman range. Our room-by-room sizing guide covers matching output to space.
Why homeowners make the switch
Real supplemental heat instead of heat lost up the flue; no logs, ash, or smoke; instant on-and-off control. Kingsman specifies that both Millivolt and ProFlame II electronic (IPI) ignition operate during a power failure with adjustable flame, so you keep heat and ambiance when the power is out — something a furnace cannot promise. A blower requires power and will not run.
A reality check before you buy
An insert only works if you have an existing masonry fireplace to put it in, and only if your opening meets the minimums above. If you are adding a fireplace where none exists, or you want a modern linear or see-through look, a zero-clearance unit is the right path. Installation should be performed by a licensed gas installer to meet local code and protect your warranty.
Send us your opening measurements
Width, height, and depth of your existing firebox — measured at the narrowest point. We will tell you which inserts fit and which fronts work with your depth.
Call +1 (877) 879-9191 (Mon–Fri, 8:00 AM–5:00 PM ET) or email support@lumiflares.com.
Frequently asked questions
What size opening do I need for a gas fireplace insert?
At minimum 24 1/4" wide by 18 1/2" high by 14" deep for the smallest Kingsman IDV24. Larger inserts need more: the IDV44 requires 32 7/8" by 25 3/4" by 18".
Can I convert a prefab metal fireplace to gas?
Not necessarily. Inserts are specified for masonry fireboxes. If yours is a prefabricated metal unit, check with us before ordering — the answer depends on the original appliance and local code.
How do I measure my fireplace opening?
Measure width, height, and depth at the narrowest point of the firebox. Masonry fireboxes commonly taper toward the back, so the rear width is often the limiting dimension rather than the front.
Does a gas insert work during a power outage?
Yes. Kingsman specifies that both Millivolt and IPI valve systems operate during a power failure with adjustable flame control. The blower requires power.
Sources
Specifications drawn from the Kingsman Fireplaces United States Price List effective March 1, 2026, and the IDV24/34/44 and IDV26 installation manuals.
