Two rectangles, and they are not the same rectangle
There are two footprints in a stove installation and confusing them is the usual source of a pad that is the wrong size. One is the hearth pad, which is the appliance footprint grown by the extension dimensions in the listing. The other is the clearance envelope, which is the appliance grown by the clearance-to-combustibles dimensions, and it is very much larger. The pad protects the floor; the clearance envelope is the volume nothing combustible may occupy. They overlap and they do not match.
On the numbers the form opens with: a 26 by 22 inch appliance with 8 inches of extension each side and 16 in front gives a pad of 42 by 38 inches, which is 11.08 square feet, with 160 inches of edge to trim. The clearance envelope is a different shape: 26 plus 14 each side is 54 inches of wall run, and 16 behind plus 22 of stove plus 36 in front is 74 inches out into the room. In a 120 inch deep room that leaves 46 inches, which is a walkway and not much else.
| Dimension | From the wall | In feet and inches |
|---|---|---|
| Appliance back | 16 in | 1' 4" |
| Appliance front face | 38 in | 3' 2" |
| Pad front edge | 54 in | 4' 6" |
| Front clearance line | 74 in | 6' 2" |
The corner install and where the 1.414 comes from
Turning an appliance 45 degrees into a corner buys room, and the arithmetic is tidier than it looks. Hold the rear clearance to both walls at once and the run taken up along each wall from the corner comes out as the width plus the depth, divided by the square root of two, plus the rear clearance. On the defaults that is 26 plus 22 over 1.414, which is 33.94, plus 16, giving 49.94 inches along each wall. The appliance front reaches 57.63 inches out along the diagonal from the corner, and the front clearance line reaches 93.63.
The pad is the same rotated rectangle, 42 by 38, and if you are buying a square blank to cut it from, the bounding square of that rectangle at 45 degrees is 42 plus 38 over 1.414, which is 56.57 inches, or 4 feet 8 and 9 sixteenths on a side. Corner pads are normally cut as a five-sided piece rather than a square, so that figure is what to buy rather than what it ends up looking like.
The word combustible does more work than people expect
Clearance is measured to combustibles, not to the wall surface. The studs behind the drywall are combustible. So are the sheathing, the floor joists under the pad, a wooden mantel, the trim above the appliance and the stair stringer on the other side of a partition wall. Heat reaches all of them without the visible surface ever feeling more than warm, and wood exposed to moderate heat for long enough changes character and ignites at a much lower temperature than new lumber does. That process takes months or years and gives almost no warning from the room. It is one of the recognised ways houses with wood heat burn down, and it is exactly why the clearance figures live in a listing that was arrived at by testing rather than in a rule of thumb.
This page names the hazard and stops. It has no procedure for assessing a wall, no view on shields, no opinion on what reductions might be permitted, and no ability to tell you whether anything you are planning is acceptable. Those figures come from the listing for your specific appliance and from the code your jurisdiction has adopted, and the building department and a certified installer are the ones who apply them.
Floor protection is a build-up, not just an outline
Getting the pad outline right is half of it. The listing also states a thermal requirement, usually either an R-value the assembly under the appliance has to reach or a specific material and thickness by name, and a correctly sized pad with the wrong build-up is not floor protection at all. This calculator deliberately does not compare an R-value you have against an R-value you need, because putting those two numbers side by side is a verdict, and a verdict on floor protection is not something a web page can responsibly issue. Take the listing to your installer and your inspector.
Before the pad, the chimney
The order that saves money is chimney first, appliance second, pad third. An existing chimney has to be inspected by a certified sweep before anything is connected to it, and what that inspection finds regularly changes which appliance is sensible, which changes the footprint, which changes the pad. The flue size calculator covers matching the appliance outlet to the flue, the chimney draft calculator covers what the flue is physically doing, and the wood stove sizing calculator covers whether the appliance suits the room at all. None of them, including this one, tells you that an installation is safe.
Questions people ask
Where do I get the clearance numbers?
From the installation instructions for the specific appliance, which is the document that has the tested figures in it, and from the code your jurisdiction has adopted. They are not general values and they differ enormously between models and between the same model with and without a rear heat shield. This page states none of them and has not checked the ones you typed against anything. If the paperwork is missing, the manufacturer will usually supply it for a model number, and a certified installer or the building department is where to go next.
Is the hearth extension measured from the stove or from the door?
That depends on the appliance and the listing says which, and the difference matters because it can be several inches. Some listings measure the front extension from the appliance body, some from the fuel loading door, and some specify both a front and a side dimension measured from different references. Read that line carefully before ordering material, because it is a common and expensive misreading.
Can I count the existing floor as part of the protection?
This page will not answer that, and it is not a question arithmetic settles. Floor protection has a thermal requirement stated in the listing as an R-value or as a named material and thickness, and what an existing floor contributes to that is a matter for the installer and the inspector looking at the actual assembly. The calculator does the outline only and takes no position on any build-up.
How much room do I really lose to a corner install?
On the default appliance, 49.94 inches of run along each wall from the corner, and the front clearance line reaching 93.63 inches out along the diagonal. Against the wall install that is a 54 inch wall run and 74 inches into the room. The corner gains you a usable wall and costs you a diagonal, so which one wins depends on the room. Chalk both on the floor before deciding; it takes ten minutes and it is the cheapest part of the whole project.
How many tiles do I need for the pad?
On the defaults, a 42 by 38 inch pad is 1,596 square inches, and at 12 by 12 inch tiles with 10 percent waste that is 13 pieces from a bare 11.08. Treat that as a floor and not an order, because a count from area alone ignores where the cuts land, and a pad with a diagonal edge for a corner install wastes far more than ten percent. Draw the layout on the real dimensions, and buy from a single batch so the colour matches.