Firebrick Compared: Which Brand Should You Buy?

Finding the right wood heating appliance is critical. Whether you choose a wood stove or a wood burning furnace, you’re going to rely on your heater to provide warmth during the blistering cold. The last thing you want to do is make the wrong decision.

An overlooked component of the purchasing process, though, is choosing the right firebrick to put in your appliance. The brick is almost as important as the stove or furnace itself. It protects and insulates the firebox, and it has a direct effect on how heat is transferred throughout your home.

At HY-C, we produce a couple of wood burning furnace models under our Fire Chief and Shelter brand names. In our furnaces, we use a private-label firebrick produced by Alsey Refractories Co., one of the leading firebrick manufacturers in the world.

Recently, we asked an industry partner to run in-depth scientific analyses on three popular firebricks commonly used in wood furnaces and wood stoves throughout the country:

• Alsey Smithfield Firebrick
• Cleveland Iron Works Firebrick
• US Stove Company Pumice Firebrick

In this guide, we’re going to explain the testing methods used on each brick. We’ll also provide some insight into how each brick may perform in a wood burning furnace based on the test results. By the time you’re finished here, you’ll be able to decide which kind of firebrick to use in your wood heating appliance.

VIEW RAW TESTING DATA

Firebrick Testing Methodology

The tests included 15 firebricks — 5 from each manufacturer. Here's what the testing process included:

• Baseline measurements of each brick
• Modulus of rupture (MOR) tests
• Cold crushing strength (CCS) tests
• An insulative test

Throughout this guide, we’ll take a close look at each test, how they were performed, and how to interpret the results.

Note that numbers and measurements presented throughout this report represent average results of each of the five bricks from each company.

For example, the weights of the five Alsey bricks were:

• 3.93 pounds
• 3.81 pounds
• 3.75 pounds
• 3.80 pounds
• 3.85 pounds.

For this measurement, we’ll use the average weight of all five bricks — 3.83 pounds — to represent weight for all Alsey firebrick (for the sake of brevity).

Baseline Firebrick Measurements

To begin, some preliminary measurements of all 15 bricks were taken, including:

• Their length, width, and thickness (in inches)
• Their weight (in pounds)
• Their average density (in pounds per cubic feet)
  • Note: density is derived from dimensions and weight

These measurements can be taken by virtually anybody with even relatively basic equipment. Here are the results:

What It Means

For firebrick, density is an indication of strength. The denser the brick, the better it will hold up in the long run, especially as you constantly throw firewood on top of it in your firebox.

Less dense brick is more likely to crack and crumble. That means as the brick breaks, you’ll have to replace it more often.

From the results, we can conclude that:

• Alsey Refractories Co. had the densest firebrick
• Cleveland Iron Works firebrick followed closely behind Alsey in terms of density
• US Stove Company firebrick was the least dense at less than half the density of Cleveland Iron Works firebrick

Firebrick Modulus of Rupture (MOR) Test

“Modulus of rupture” is a complicated-sounding phrase, but the test is much simpler than its name suggests.

In this test, the firebrick is placed on two resting points with empty space underneath the middle of it. Pressure is then applied from the top down until the brick breaks.

The measurement derived from this test is the highest amount of pressure the brick was able to handle before it broke (in pounds per square inch, or psi). Here are the results:

What It Means

Like density, modulus of rupture is a good test of the strength and longevity of firebrick, especially with regard to how the brick is able to handle pressure at its weakest point: its center.

Like density, it’s also an indicator of impact-resistance, or how well the brick will hold up as you throw logs into your stove or furnace day after day.

Firebrick that breaks under lower pressure is more likely to fracture during regular use in a wood furnace or wood stove. Regarding our three firebrick manufacturers, we can conclude:

• Alsey Refractories Co. brick was able to withstand the highest amount of pressure before breaking
• Cleveland Iron Works lagged behind Alsey quite a bit, handling 370 psi less before rupturing
• US Stove Company firebrick withstood the least amount of pressure, handling less than half the pressure of Alsey brick and nearly 150 psi less than Cleveland Iron Works brick

Firebrick Cold Crushing Strength (CCS) Test

A cold crushing strength test is similar to a modulus of rupture test with one key difference: instead of resting on two points of contact with empty space under the center of the brick, the entire bottom surface area of the brick simply rests flat on a surface.

Other than that, CCS and MOR tests are essentially the same: pressure is applied to the brick from the top down until it breaks. We also derive a similar measurement from a CCS test as we do from an MOR test: the amount of pressure (in psi) that the brick was able to withstand before breaking.

Because the bottom of the brick rests on a much larger surface area in a CCS test than an MOR test, it’s able to handle much more pressure before breaking.

Here are the results for Alsey, Cleveland Iron Works, and US Stove firebrick:

What It means

This is yet another test of structural strength.

It may seem redundant, but users expect firebrick to last in their furnace or stove for burning season after burning season. A CCS test is a bit more realistic than an MOR test in terms of what the firebrick may actually experience (and, therefore, how it may actually behave) in a wood heater.

A full load of wood in a furnace is heavy. The better the firebrick performs in a CCS test, the more likely it is that that brick will hold up in the long run under a load of wood.

From the test results, we can conclude:

• Alsey Refractories Co. firebrick withstood the most pressure before being crushed
• Cleveland Iron Works firebrick was close to Alsey but still trailed by more than 3,000 psi
• US Stove Company firebrick withstood over four times less pressure than Alsey or Cleveland Iron Works brick

Firebrick Insulative Test

Let’s dive into how each brick actually handles and transfers heat — obviously an important consideration for a wood burning furnace or wood stove application.

This test consisted of running a handheld propane torch against each firebrick for a half hour. A temperature gun was utilized to take temperature readings every two-and-a-half minutes to measure the temperature of the side of the brick being subjected to the torch (in degrees Fahrenheit):

At the same two-and-a-half-minute intervals, a temperature gun was also used to measure the temperature of the surface of each firebrick not being subjected to the torch (in degrees Fahrenheit):

With this data, we can divide the temperature on the cold side of the brick by the temperature on the hot side of the brick at each two-and-a-half-minute interval to find the insulating percentage of each brick over time:

What It Means

Insulating percentage is a measurement of the effectiveness of firebrick’s ability to transfer heat. Firebrick acts as an additional heating element in the firebox. In a wood furnace, the hotter the outside of the firebrick gets, the more efficiently it transfers heat up into the ductwork.

Or, put more simply, the higher the insulating percentage, the better the firebrick performs in terms of heating your home.

From the test data, we can conclude:

• At the half-hour mark, Alsey firebrick reached the highest insulating percentage at 56.23%
• At the same point, Cleveland Iron Works brick was slightly behind at 47.42%
• After a half hour, US Stove firebrick’s insulating percentage was 29.42% — nearly half that of Alsey brick

This means that in terms of efficiently distributing the most heat, Alsey brick leads the pack, with Cleveland Iron Works just slightly behind. US Stove firebrick’s heating efficiency falls significantly behind Alsey and Cleveland in terms of heat transfer capabilities.

Which Firebrick Should You Buy?

That was a deep, deep dive on three of the industry’s most-used firebricks. There’s a lot of data to dissect, and there’s even more to see in the raw data that we didn’t have time to cover here.

So, with all of this in mind, which firebrick should you buy?

It’s clear that Alsey firebrick exceeds the competition both in terms of strength and heat retention. Cleveland Iron Works is not too far behind in every test category, while US Stove falls behind both competitors in every instance — sometimes by a wide margin.

That said, wood burning is just as much an art as it is a science. Beyond all the numbers, tests, and data, there may be some performance aspects of one brick that you may prefer over the others.

Our best advice is to take these results for what they are, but be sure to experiment with each brick to find what you like and dislike from each for your specific application. Once you’ve made that decision, you’ll be able to use the brick you prefer in your wood heating appliance every fall and winter heating season.

Ready to give Alsey firebrick a try? Use the product locator below to find some HY-C firebrick! Each one is made in the USA by Alsey Refractories Co. just 80 miles north of HY-C headquarters. We stand behind their performance, and we’re proud to use them in our wood burning furnaces.