Short answer: The Kingsman IDV26 fits a fireplace opening at least 19 1/2 in. high and 14 1/4 in. deep, with a back wall at least 22 in. wide. The front width you need depends on the front style: 33 in. for slim fronts with the insert centered (31 in. if it sits off-center), or 28 in. with a wide front. You also need a chimney between 12 ft and 40 ft tall and a non-combustible hearth.
The four measurements
Take all four inside the firebox, not across the outer brick face. Measure in at least two places and use the smallest number.
- Front width. Side to side at the front of the opening.
- Back width. Side to side along the back wall. Most masonry fireboxes taper, and this is the measurement people skip.
- Height. From the firebox floor to the underside of the lintel, the lowest point at the top of the opening.
- Depth. From the front edge of the opening to the back wall, at floor level and again about 20 in. up. Many back walls slope forward, so the upper number is often smaller.
Kingsman's minimums for the IDV26
| Measurement | Slim fronts (controls inside the opening) | Wide fronts (controls outside the opening) |
|---|---|---|
| Front width | 33 in. centered, or 31 in. off-center | 28 in. |
| Height | 19 1/2 in. | 19 1/2 in. |
| Depth | 14 1/4 in. | 14 1/4 in. |
| Back width | 22 in. | 22 in. |
From Kingsman installation manual 26IDV-MAN17, IDV26 Insert Dimensions and Sizing.
Why the width has two answers
The IDV26 ships with its gas valve and controls mounted beside the firebox, inside your fireplace opening. Kingsman calls this Components In, and it is why the slim fronts need 33 in. of width when the insert is centered. If you can accept the insert sitting slightly off-center, 31 in. works.
For narrower openings, the installer can move the controls outside the opening, which Kingsman calls Components Out. The controls then sit on the face of the fireplace and must be covered by one of the wide fronts. That drops the minimum width to 28 in. The relocation has to be done before the insert goes into the fireplace.
Which front goes with which opening
- 31 in. or wider: any front. Slim, Slim Deep and Slim Picture Frame keep the look tight to the opening.
- 28 in. to under 31 in.: Wide or Wide Picture Frame only.
- Under 28 in.: the IDV26 will not fit. Look at a smaller insert in our gas insert collection.
- Uneven or protruding masonry: the Slim Deep front has a deeper profile to bridge it.
- Large or tall openings: the Picture Frame fronts add a bigger surround to cover the gap. The front has to overlap the opening on all sides, so send us your outer opening size and we will confirm coverage.
Three more checks before you order
1. Chimney height
The insert vents through two 3 in. flex liners that run up your chimney to a cap at the top. Kingsman requires a vertical run of at least 12 ft and no more than 40 ft, with a maximum of 2 ft of horizontal offset. Measure from the firebox floor to the top of the chimney. A chimney that burned wood has to be professionally cleaned before the liners go in, and the insert cannot share a flue with another solid-fuel appliance.
2. Hearth and floor
The floor under the insert must be non-combustible. Kingsman also requires a hearth in front that is at least 3/4 in. thick, 12 1/2 in. deep and 31 in. wide. If the firebox floor is uneven, the IDV26 has two leveling legs at the back.
3. Mantel and wall above
Combustible mantels have minimum heights that increase with how far the mantel projects. In the manual the lowest combustible mantel position is 35 3/8 in. above the bottom of the unit, rising to 45 3/8 in. for the deepest mantel shown. Kingsman's optional mantel clearance shield lowers those heights by 6 7/8 in. Wall finishes below the combustible mantel line must be non-combustible. Have your installer read the exact figures from the mantel clearance diagram for your mantel depth.
Also plan for
- Power: a grounded 120 V outlet for the standard blower.
- Gas: the line can enter from the left or right. In a factory-built fireplace with no gas access hole, the manual allows one hole of 1 1/2 in. or less through the lower side or bottom, sealed with non-combustible insulation afterward.
- The existing fireplace: the damper is removed or fixed open, and grates, glass doors and screens come out. In a factory-built fireplace, cutting any sheet-metal parts is prohibited.
- Cold exterior chimneys: Kingsman recommends insulating the chimney cavity with non-combustible insulation in cold climates so the insert lights reliably.
What to send us
Email or call with these and we will confirm fit and the right front, usually the same day:
- Front width, back width, height and depth of the firebox
- Chimney height and whether it is on an outside wall
- Natural gas or propane
- A photo of the fireplace, including the hearth and mantel
Call 877-879-9191 or contact us. For the full picture of the unit itself, read our Kingsman IDV26 review or go to the IDV26 product page. For what installers charge and why, see how to read a gas fireplace quote.
Frequently asked questions
What is the minimum fireplace opening for the Kingsman IDV26?
33 in. W x 19 1/2 in. H x 14 1/4 in. D with a slim front and the insert centered, or 28 in. W x 19 1/2 in. H x 14 1/4 in. D with a wide front. The back of the firebox must be at least 22 in. wide.
My opening is 30 in. wide. Can I still use the IDV26?
Yes, with a Wide or Wide Picture Frame front and the controls relocated outside the opening.
How tall does my chimney need to be?
At least 12 ft and no more than 40 ft of vertical vent run.
Do I need a hearth?
Yes. Kingsman requires a non-combustible floor under the unit and a hearth at least 3/4 in. thick, 12 1/2 in. deep and 31 in. wide.
Source: Kingsman installation manual 26IDV-MAN17 for the IDV26. Codes vary by jurisdiction. This article does not replace the manufacturer instructions or a licensed installer.