Brass, a family of copper-zinc alloys, has a thermal conductivity that typically falls in the range of about 109 to 120 W/(m·K) for the most common compositions, roughly a quarter to a third of pure copper’s value. That range shifts considerably depending on how much zinc is in the mix, how the material has been processed, and what temperature it is operating at. For engineers picking a material and for anyone curious about why brass door handles feel the way they do, understanding what drives these numbers matters more than memorizing a single figure from a reference table.
Why Brass Conducts Less Heat Than Pure Copper
Pure copper sits near the top of the thermal conductivity chart for common engineering metals, around 385 to 400 W/(m·K) at room temperature. The moment you dissolve zinc atoms into the copper lattice, those foreign atoms disrupt the orderly crystal structure. Electrons and the vibrations of the crystal lattice (phonons) both carry heat through a metal, and zinc atoms scatter both of these carriers. The result is a steep drop in thermal conductivity compared to the parent metal.
Research separating the electronic and phononic contributions to heat flow in metals and alloys has shown that phonons actually absorb and transmit the majority of incoming heat, even in metallic systems where electrons are usually assumed to dominate thermal transport.1International Journal of Modern Physics B. Isolating lattice from electronic contributions in thermal transport measurements of metals and alloys above ambient temperature and an adiagonal model This is relevant to brass because the zinc atoms are particularly effective at scattering phonons, which helps explain why even modest zinc additions cause a disproportionately large conductivity penalty.
How Zinc Content Shapes the Numbers
You might expect thermal conductivity to drop smoothly as zinc content increases, following a simple dilution logic. The reality is more interesting. First-principles calculations of copper-zinc binary alloys show that both electrical and thermal conductivities follow a non-monotonic trend with increasing zinc: they initially decrease and then increase, a pattern that matches available experimental data.2PubMed Central. First-Principles Study on the Electrical and Thermal Conductivities of Cu–Zn Binary Alloys The dip occurs because at low zinc concentrations, each added zinc atom acts as a strong scattering center in a mostly copper lattice. Once the alloy develops its own stable crystal structure at higher zinc fractions, the lattice becomes more regular again, and conductivity partially recovers.
In practical terms, a brass with about 30% zinc (such as cartridge brass, C26000) tends to sit near the bottom of the conductivity curve for alpha brasses. Alloys with 10% or 15% zinc, like gilding metal or red brass, preserve more of copper’s conductivity, sometimes exceeding 150 W/(m·K). Meanwhile, brasses pushed above 35% zinc enter mixed-phase territory where the crystal structure changes altogether, and conductivity depends on which phases are present and how they are distributed.
Comparing Brass to Other Common Metals
The usual reason someone looks up brass thermal conductivity is to compare it against alternatives. Aluminum sits at roughly 205 to 237 W/(m·K) depending on the alloy, making it about twice as conductive as most common brasses. Pure copper, as noted, is roughly three to four times more conductive. Stainless steel, on the other hand, comes in around 15 to 16 W/(m·K), which is roughly a seventh to an eighth of a typical brass.
An experimental study comparing heat conduction through brass, copper, and aluminum rods found that brass exhibited the largest overall temperature drop along the bar’s length (from 58 °C at the heated end down to 27 °C), while copper showed the most uniform thermal decline, dropping from 55 °C to 28 °C. Aluminum fell between the two, going from 58 °C to 29 °C.3International Journal of Engineering Materials and Manufacture. Experimental and Finite Element Analysis of Heat Conduction of Brass, Copper and Aluminium The steeper gradient in brass tells you heat is moving through the material more slowly, creating a larger temperature difference between the hot source and the cooler end. This is a useful intuition: brass acts as a partial thermal bottleneck compared to copper or aluminum, which is sometimes exactly what a designer wants.
In direct measurement experiments, the rate of heat energy transferred through a brass rod was about 0.81 J/s, compared with only about 0.09 J/s for a 304 stainless steel rod of comparable geometry.4Proceedings of the 2nd International Seminar of Science and Applied Technology. Experiments for Determining the Thermal Conductivity of Brass and 304 Stainless Steel with Direct Temperature Measurement Techniques Using Lorenz Number as Validation That roughly ninefold difference captures the practical gap between brass and stainless steel: brass moves heat far more readily, which is why it shows up in applications where stainless steel’s corrosion resistance alone is not enough to justify the thermal penalty.
What Happens at Low Temperatures
Thermal conductivity in metals does not hold steady as temperature drops toward absolute zero. In brass alloys, the physics at cryogenic temperatures is quite different from what happens at room temperature. Measurements of copper-zinc alloys containing up to 30% zinc across a wide range of low temperatures found that below about 10 K, the lattice (phonon) component of thermal conductivity is limited primarily by two scattering mechanisms: phonons colliding with conduction electrons, and phonons interacting with dislocations in the crystal structure. At somewhat higher temperatures within the cryogenic range, point defects (the zinc atoms themselves) become the dominant limiters of lattice conductivity.5Acta Metallurgica. The electrical and thermal conductivities of some brasses at low temperatures
This matters to anyone designing cryogenic equipment. At very low temperatures, the thermal conductivity of brass can be dramatically lower than its room-temperature value, and small differences in composition or processing history can shift the numbers significantly. A brass tube that performs perfectly well as a thermal bridge in a room-temperature heat exchanger may become an effective thermal insulator when cooled to liquid-helium temperatures, which is useful if you are trying to limit heat leakage between temperature stages in a cryostat.
How Processing Changes Conductivity
Two pieces of brass with identical compositions can have noticeably different thermal conductivities depending on their processing history. Cold working, where the metal is deformed at room temperature by rolling, drawing, or stamping, introduces dislocations and lattice strain that scatter heat carriers. The result is a measurable drop in thermal conductivity compared to a well-annealed piece of the same alloy.
Annealing reverses much of this damage. The same low-temperature conductivity study on brasses found that lattice conductivity at all measured temperatures was markedly increased by annealing.6Acta Metallurgica. The electrical and thermal conductivities of some brasses at low temperatures Heat treatment allows atoms to rearrange into a more regular crystal lattice, reducing scattering. For any application where thermal performance is critical, specifying the temper (soft, half-hard, hard) is not just about mechanical strength; it directly affects how well the part conducts heat.
This relationship between processing and conductivity is one reason that reference tables for brass thermal conductivity sometimes disagree with each other. A value measured on a freshly annealed sample may not match a value measured on a cold-drawn tube, even if both are nominally the same alloy grade. If you are designing something thermally sensitive, asking your supplier about the material’s condition is as important as knowing the alloy number.
Brass in Heat Exchangers and Condensers
Brass has been a mainstay of heat-exchanger tubing for over a century, particularly in marine condensers and HVAC systems. Its combination of decent thermal conductivity, corrosion resistance in many water chemistries, and ease of fabrication has kept it competitive even as alternatives have multiplied. But the actual thermal conductivity of the tube wall turns out to matter less than you might assume in many condensing applications.
A study of dropwise condensation on horizontal tubes made of copper, brass, aluminum, and stainless steel found something initially surprising: after accounting for tube-wall thermal resistance, the overall heat-transfer coefficients for copper, brass, copper-plated brass, copper-plated aluminum, and copper-plated steel tubes were essentially the same.7International Journal of Heat and Mass Transfer. Effect of condenser tube material on heat transfer during dropwise condensation of steam The researchers attributed previously reported differences between tube materials to differences in how effectively the surface promoter worked on each substrate, not to the thermal properties of the metal itself. In other words, in condensing service, the surface condition and the condensation mode (dropwise versus filmwise) dominate performance, and the tube-wall material’s thermal conductivity plays a secondary role.
This finding is a good reminder that thermal conductivity in isolation does not determine system performance. A brass condenser tube with a well-prepared surface can transfer heat as effectively as a copper one, even though copper’s bulk conductivity is several times higher. The thermal resistance of a thin tube wall is small compared to the resistance of the fluid boundary layers on either side, so the wall material’s conductivity makes less difference than intuition suggests.
When Brass Is Chosen Over Higher-Conductivity Alternatives
If pure copper conducts heat three or four times better, and aluminum about twice as well, why use brass at all in thermal applications? Several factors tip the balance.
- Machinability: Free-cutting brasses (like C36000) machine far more easily than copper, which is gummy and difficult to turn to tight tolerances. For parts like valve bodies, fittings, and instrument housings where complex geometries are needed, brass wins on manufacturing cost even if it loses on raw conductivity.
- Corrosion resistance: Brass resists dezincification, stress-corrosion cracking, and general corrosion in many water chemistries better than bare copper or aluminum, depending on the alloy grade. In marine and plumbing environments, that longevity can matter more than peak thermal performance.
- Controlled heat flow: Sometimes you want moderate conductivity, not maximum conductivity. Brass soldering tips, brewing equipment, and certain sensor housings benefit from a material that conducts heat well enough to be responsive but does not dump energy so quickly that temperature gradients become unmanageable.
- Spring and strength: Some brasses, especially tin-bearing and silicon-bearing varieties, offer spring properties or tensile strength that copper and aluminum cannot match. In connectors and thermal switches, the combination of acceptable conductivity and good mechanical properties is the deciding factor.
Aluminum is the most common competitor to brass in heat sinks and heat exchangers, offering better conductivity at lower weight. But aluminum is notoriously difficult to solder with conventional methods, corrodes in alkaline environments, and cannot be threaded as cleanly for plumbing connections. Each application involves a trade-off matrix where thermal conductivity is one variable among many.
Common Misconceptions About Brass and Heat
One persistent misunderstanding is that brass is a “good conductor of heat” in some absolute sense. It is a good conductor compared to steel, ceramics, and plastics, but a mediocre one compared to the metals it is most often measured against. People sometimes assume brass cookware will heat as evenly as copper-clad pans, or that brass radiator fittings will transfer heat as efficiently as copper ones. In practice, brass fittings in a hydronic heating system add negligible thermal resistance because the fitting walls are thin and the fluid-side resistances dominate, but a thick brass plate used as a heat spreader would underperform a copper or aluminum one of the same dimensions.
Another misconception involves the feel of brass objects. Brass doorknobs and handrails feel cold to the touch because brass conducts heat away from your skin faster than wood or plastic, but people sometimes interpret this as meaning brass is an exceptionally good conductor. The cold feeling is a comparison to insulators, not to other metals. A copper doorknob would actually feel slightly colder because it draws heat from your hand even faster, though the perceptual difference is small.
A subtler error is treating thermal conductivity as a fixed property of “brass” without specifying the alloy. Quoting 109 W/(m·K) as the thermal conductivity of brass is like quoting a single number for the hardness of steel: it depends enormously on which brass you mean. The spread from a low-zinc gilding metal to a high-zinc muntz metal can be a factor of two or more in conductivity, and knowing which end of the family you are dealing with is essential for any quantitative thermal design.
The Wiedemann-Franz Connection
Because electrons carry both electrical current and much of the heat in a metal, thermal conductivity and electrical conductivity tend to track each other. This relationship, known as the Wiedemann-Franz law, says that the ratio of thermal to electrical conductivity at a given temperature is roughly constant across metals. For brass, this means you can get a reasonable estimate of thermal conductivity if you know the electrical resistivity, and vice versa.
Experimental work has validated this approach for brass. One study measured the thermal conductivity of brass directly and then checked the result against the Wiedemann-Franz prediction by computing the Lorenz number, finding reasonable agreement, though with some scatter reflecting real-world measurement uncertainty.8Proceedings of the 2nd International Seminar of Science and Applied Technology. Experiments for Determining the Thermal Conductivity of Brass and 304 Stainless Steel with Direct Temperature Measurement Techniques Using Lorenz Number as Validation The practical upside is that electrical resistivity data for brass alloys is abundant and cheap to measure, so engineers can use it as a proxy when direct thermal conductivity measurements are unavailable for a specific alloy or temper.
The Wiedemann-Franz relationship also explains why the non-monotonic trend observed in computational studies of Cu-Zn conductivities applies to both electrical and thermal properties simultaneously.9PubMed Central. First-Principles Study on the Electrical and Thermal Conductivities of Cu–Zn Binary Alloys The same electron-scattering physics that causes electrical resistivity to peak at intermediate zinc levels causes thermal conductivity to dip at roughly the same compositions. If a brass alloy is a poor electrical conductor for its class, it is almost certainly a poor thermal conductor too.
Picking the Right Brass for Thermal Applications
If your design requires brass and you want to maximize thermal performance, lean toward low-zinc alloys. A 90/10 copper-zinc brass retains much more of copper’s conductivity than a 60/40 alloy, and it is still meaningfully easier to machine than pure copper. Red brass (about 85% copper, 15% zinc) offers a practical midpoint: noticeably better conductivity than yellow brass, with improved corrosion resistance in many water chemistries and good formability.
Specifying the temper also matters. A fully annealed (soft) condition restores the most ordered crystal lattice and gives the highest conductivity for a given composition. If mechanical strength requirements force you into a harder temper, recognize that you are trading some thermal performance for that strength. In components where both matter, heat treating after final forming can recover some of the conductivity lost during cold work.
For extreme environments, composition nuances become critical. Naval brass adds a small amount of tin for seawater resistance, while leaded brasses sacrifice some conductivity for machinability. Silicon brasses and aluminum brasses introduce additional alloying elements that further disrupt the lattice and reduce thermal conductivity. In every case, the alloy designation tells you more about expected thermal performance than the word “brass” alone ever could.