The best steel entry doors use two galvanized steel skins, 20 gauge or heavier, wrapped around an insulated foam core. Gauge is the number to read first: 24 gauge measures 0.0239 inch and 20 gauge measures 0.0359 inch, so the lower number is the thicker, harder to dent skin. The core, the glass and the frame decide the rest.
Three things decide the door you end up with: the gauge of the skin, the core behind it, and the frame it hangs in. Take them in that order and the rest of the choices get easier.
What Gauge Means, and Which One to Buy
Gauge runs backward. The higher the number, the thinner the steel. Most doors sold for homes use a 24 gauge skin, and 20 gauge is the step up that makes a real difference to how easily the face dents.
| Gauge | Thickness | On a front door |
|---|---|---|
| 24 | 0.0239 inch | The common entry level, and the easiest to dent |
| 22 | 0.0299 inch | A modest step up |
| 20 | 0.0359 inch | About half again as thick as 24, and the practical choice for a home |
| 18 | 0.0478 inch | More typical of commercial and security doors |
| 16 | 0.0598 inch | The heaviest common gauge, rarely needed at home |
The table above uses the manufacturers’ standard gauge for sheet steel. Galvanized sheet runs a few thousandths of an inch thicker at each gauge, but the order never changes: a smaller number always means more steel.
Ask for the gauge in writing. It is the one number on a door quote you can hold against another quote, and a showroom door rarely carries a label saying which one it is.
If steel is already settled for you, the steel exterior door replacement page sets out what you can choose from.
How the Foam Core Keeps the Cold Out
Steel on its own conducts heat well, which is exactly why nobody builds a front door from solid steel. The skins are thin, and the space between them is filled with foam, usually polyurethane. The steel is there for strength. The foam is there for comfort.
Heat gets out at the edges and through the glass. Weatherstripping around the frame and a sweep along the bottom close the gaps, and any glass panel insulates far less than the foam around it. A solid slab with a tight seal is the warmest option you can buy.
Through a St. Louis winter, a worn sweep is usually the first place you feel it. The steel itself will not warp or crack in a hard freeze, which is where it has the edge over wood.
If energy use matters to you, ask for the U-factor of the exact door you are quoted, and whether that style carries an ENERGY STAR label. Ask for the number on the unit you are buying, not a claim about the range it came from.
Where the Security Really Comes From
A steel skin is hard to cut or kick through, and it does not split along a grain the way a wood panel can. Measured on the slab alone, it is the most secure common front door material.
A forced entry rarely goes through the slab, though. It goes through the frame. The strike plate, where the bolt meets the jamb, and the hinges are what usually give way, because on many doors their screws only bite into the thin jamb rather than the wall framing behind it. A heavy slab hung in a weak frame is a strong panel on a weak hinge line.
On an old door the strike plate is the first thing I look at, because the screws that come in the box are often only 3/4 inch long and stop in the jamb. Screws long enough to reach the framing behind it cost almost nothing and change what it takes to kick the door in.
You cannot see any of that in a showroom, so ask whoever quotes you how the strike plate gets anchored. The steel entry door installation page covers what a fitting includes.
The Downsides of a Steel Door
- It dents, and a dent shows. A knock from a hand truck, a ladder or hail can leave a mark in steel that fiberglass would shrug off. A heavier gauge resists it but does not prevent it.
- A deep scratch can rust. The zinc coating on galvanized steel protects it, but a scratch through both the paint and the zinc exposes bare metal. Touch it up promptly, especially low on the door where water sits.
- A dark finish gets hot. A dark door facing south or west can become hot to the touch through a Missouri summer, and sustained heat is hard on the paint. Lighter colors run noticeably cooler.
- Wood grain works from the street, less so up close. Embossed steel reads as wood from the curb. At arm’s length, fiberglass generally carries a grain more convincingly.
- It cannot be trimmed to fit. A wood door can be planed a little to suit an opening that has moved. Steel cannot, so the opening has to suit the door.
When I’d Point You to a Different Door
Steel is not for every entrance, and these are the four where I would say so.
- A door that takes daily knocks. A side entrance you carry tools, bikes or strollers through will collect dents. Fiberglass holds up better to that traffic.
- A stained wood look up close. If you want a grain you can stand next to, fiberglass carries it better, and real wood better still.
- A dark color in full afternoon sun with no porch or overhang. Pick a lighter color, or a material that takes the heat better.
- An opening you want to keep exactly as it is in an older house that has settled. Steel will not be trimmed to suit it, so either the opening gets squared up or another material fits it.
If that leaves you weighing the two materials against each other, you can see them side by side in fiberglass vs steel doors.
Glass and Sidelights
Glass changes this door more than any other option. It brings light into a dark hallway, and it lowers both insulation and security compared with solid steel, because glass is the weakest part of the panel on both counts. Decorative and privacy glass keep the light while blocking the view in.
Sidelights are the narrow fixed panels that flank a door. They widen the whole unit, so adding them where there were none usually means a larger opening in the wall, not just a different door.
Standard Front Door Sizes
The standard front door in an American home is 36 inches wide by 80 inches tall, with a slab 1 3/4 inches thick. Once the frame, hinges and weatherstripping are in place, a 36 inch door leaves a clear walkway close to 32 inches wide. Widths of 32 and 30 inches are also standard, and 8 foot doors suit taller ceilings.
Older houses across St. Louis and St. Charles County have settled, and their openings are rarely square any more. When I measure one, I check all four corners rather than one width across the middle. An opening that is out of square will not take a standard unit cleanly, and a door that cannot be planed to fit leaves you two choices: square the opening up, or order to suit it.
What Moves the Price
There is no honest single price for a steel front door, because the slab is only part of what you are paying for. These are the things that move the number:
- The gauge of the skin
- Solid steel or glass, and how much glass
- Sidelights or a transom above
- A smooth face or embossed wood grain, and the color
- The frame, and whether the existing one is sound
- Whether the opening has to change size
- The lockset and hardware
When I see two quotes side by side, the first thing I check is whether both of them priced the frame and the hardware. A lower figure that leaves either one out is not a lower price, it is a shorter list.
Common Questions
Start With the Gauge, Then the Frame
Take the decisions in this order:
- Settle the gauge and the glass, because those two shape the price and everything else about the door.
- Then the frame, which decides as much about performance as the slab does.
- Then have the opening measured, so a quote covers the frame and the hardware and not the slab alone.
ProVia lists us as a Platinum dealer and a certified installer for entry doors, and you can check that yourself on their dealer locator. You get a ten year workmanship warranty on the fitting, and the steel door installation in St. Louis page covers how a visit works. Call 314-277-5952, or ask for a free estimate online, and the frame and the opening get looked at together before any price is written down. What other homeowners thought is on the reviews page.
