Classic Heaters

Heater Cores

Most people don’t think about how a heater core works until it stops working, or leaks. That’s when they realize they were taking it for granted all those cold mornings to keep their fingers and toes warm. Just try to imagine what it was like back in the 1920’s when there was no such thing as a heater core. Gloves, scarves, goggles and heavy coats were all that stood between drivers, passengers and cold winter temperatures. As civilization progressed and comfort while driving became an issue many companies sold aftermarket heater assemblies to be installed where there was nothing at all before. Car manufacturers finally started offering optional heaters in the late 1930’s. By the late 1940’s most cars came standard with some kind of a heater/defroster assembly. Some even went as far as one or more heater cores for heat and one or more just for defrosting purposes. Nowadays the heater core is an integral part of the HVAC (Heating, Ventilating, Air Conditioning) system. With electronic controls, servomotors and computers to control how much heat comes out and where, it still all depends on the heater core to provide the actual heat.

A heater core is actually a miniature radiator. With the main difference being the heat that it throws off is used to keep you warm and defrost the windshield. Hot antifreeze flows through the coolant passages and the heat transfers from the liquid to the core material. Fresh or recirculated air passes through the fins of the heater core and picks up the heat. The heated air is then directed to the floor, dash vents or defroster. In the mid 1970’s car manufacturers found out that a defroster will do its job quicker if the air can be dehumidified before blowing on the windshield. On a vehicle equipped with air conditioning this works by dehumidifying the air before it goes through the heater core. Besides making the air cold an air conditioning system removes humidity from the air that passes through the evaporator. A windshield will dry much more efficiently with dry hot air blowing on it as opposed to damp hot air.

Now that you know what a heater is supposed to do and how, lets talk about the things it’s not supposed to do. A traditional copper heater core is constructed very much like a radiator. It has tubes, fins, necks and tanks. All these parts are soldered together. The heater core is subjected to even more heat and pressure than the radiator is. In a car without a heater control valve the coolant is pushed through the heater core as soon as the engine is started. Most people are not aware of the volume of liquid that a water pump will push. It is not uncommon for a heater core to be overpressurized and start to leak if the engine is brought up to a high RPM before the thermostat opens. If the thermostat is still closed, all of the coolant is forced to go through the bypass circuit and the heater core. A stock water pump as well as a high flow water pump can easily blow out a heater core. Most heater core leaks are a result of normal wear, tear and age. Every time the engine builds up pressure the heater core expands just a little and then settles back as the cooling system cools off. Over the years the solder joints are stressed and what started out as a ¼” bead of solder becomes 1/8” and then 1/16” and then a leak. A dirty cooling system can also cause a heater core leak. If the system is excessively rusty, that rust acts as an abrasive running through the inside of the heater core. Rust is actually tiny bits of steel or cast iron. If you are constantly rubbing a hard metal like steel against a softer metal like brass, copper or solder, the softer metal will eventually lose the battle. Some heater cores can develop leaks without ever even being installed in a car.

In order to transfer maximum heat the tube walls of a heater core are made of relatively thin material. When a copper heater core is made there is a considerable amount of flux used to get all the components to solder together properly. Flux is a mild acid. If all of the flux is not flushed from the newly assembled core it will start to corrode the core from the inside out. That is why finding a 50 year old NOS heater core may not be the score you think it is.

Besides developing a leak the only other cause of a heater failure is for it to get clogged up. Rust chips, excessive gasket sealer, gasket material, lime & calcium deposits and radiator stop-leak are the primary culprits. As the heater cores internal passages become obstructed there will be less and less heat transferred from the coolant to the air flowing through the heater. Unlike a radiator, a heater core cannot be flow tested to see if it is clogged up. It can be flushed and you can see what if anything comes out but you have no way of knowing how much debris might still be in there. Reverse flushing of the heater core (and the entire cooling system) should prevent this from happening. If the system is flushed on a regular basis any debris in the heater core should come out. If it has been allowed to sit in there for years (or decades) good luck in removing it. There are filters that can be installed to prevent debris from entering the heater core but it is best to just keep the system clean and flush it out every two or three years.

A heater core is actually made from two different sizes of thin copper strip. Flat material in both .0025” and .0045” thickness is purchased in bulk rolls. The .0025” strip is run through dies that bend it into a V shape to form the fins and another machine forms the .0045” into the tube walls. The ends of the tube walls are folded over and interlocked with the adjoining tube walls to form a mechanical joint. The previously formed fins are inserted between the tubes and it is all placed in a clamp type jig. The fin/tube assembly is dipped in a tub of flux and then a tray of 900 degree 25/75 molten solder just enough for the solder to wick up about a quarter inch between the separate tube walls and solder them together. It is then flipped over and the other “face” of the core is dipped to complete the process. Replacement heater core material is generally made to a specific thickness and height in a “block” about 25” wide. The required piece is then cut off the block to whatever width is needed for a particular job.

Back in the day, new heater cores were only available from the dealer. If the heater was not available from the dealer or was too expensive it would be brought to a radiator shop to be recored. In the early 1970’s radiator manufacturers got into the mix and started to make brand new aftermarket replacement heater cores. New heater cores are still available today for many cars back into the early 1960’s. Unfortunately the quality or fit of some of these may not be as good as you would like. Due to environmental and financial concerns most copper heater cores are now made outside the US. Not to say that they are all bad but there has to be shortcuts taken to keep the price competitive and quality of material and labor sometimes suffers. If you own a classic 1950’s or older car, odds are that you will not find a complete new heater anywhere at any price. Most heater cores would only fit two or three years in a particular model before the manufacturer changed designs and came up with a whole new heater box and core design. There are many that fit one year only, which prevents aftermarket manufacturers from producing them. The expected volume of sales does not even come close to justifying the tooling required.

A heater core is recored much the same way as a radiator core. The tanks are removed by heating up the solder holding them onto the core. The tanks are glass beaded and checked for any cracks. The perimeter of the tank is tinned up to get a clean and prepped surface. A thin coat of solder is applied to either the edge of the new core material or the lip of the tank. The tank is clamped onto the core and the solder is heated until it flows and the tank is soldered to the core. The hose connections or necks are resoldered and the heater core is pressure tested. After testing, water is run through the inside of the core to rinse away any remaining flux and then the entire core is submerged in special chemical to neutralize any flux on the outside. After it is dry it is glass beaded again just to make it clean and presentable.

The often-neglected heater core should not be ignored if you are doing even a minor restoration. Antifreeze leaking onto your carpet or an oily mist on the inside of your windshield will quickly take the fun out of a cruise in your classic car or truck.


General Info

  1.  When sending a heater core for recoring be sure to include your name, address, phone number, best time to call and all pertinent vehicle information. Also let us know how you heard about Classic Heaters.

  2.  Turnaround time is usually within one week as long as we have the required piece of core in stock. If we don’t, it may take an additional week.

  3.  We might be able to quote you a price via e-mail or phone if we have the size of your heater core on file. If we don’t, you will have to send it to us for a price quote. If you are not happy with the quoted price, we will ship it back to you at no charge.

  4.  All recored heater cores come with a one year guarantee.

  5.  We accept Visa, Mastercard, American Express, Discover and money orders for payment. We suggest that you give us your credit card information over the phone instead of sending it with the heater core if that is how you will be making payment. We do accept personal checks but will require a 10 day holding period to ensure clearing.

  6.  We do not rebuild heater control valves but we highly recommend the services of these two heater valve rebuilders;

    Jim Tucker, 29596 Paso Robles Rd, Valley Center CA  92082 Phone 760-749-3488

    Old Air Products 4615 Martin St. FortWorth TX     817-531-2665


 7. Our shipping address is ; Classic Heaters, 994 Fulton St., Farmingdale NY 11735

 8.  Please let us know if you have a preference of return shipping. We use UPS on a daily basis. US Postal service can also be used if requested.

Brief History


I have always been involved with “old” cars. I got my first car a year before I even got my license. It was a 1954 Chevy BelAir. I should say “It is” because I still own it. I got it in 1977 and learned a lot about cars by screwing up while trying to fix it up. Right about the time I got it on the road in my junior year in high school I got my second car (that I still own), a 1959 Ford Fairlane 500 Galaxie.

Even at that young and stupid age I realized that It would help my interest in old cars if I got into the automotive business. In my senior year of high school I started working at a local radiator shop as a helper. By 1984 I was the owner of my own and on my way. Being the owner of a business actually slowed down my restoration efforts on my own cars due to the never-ending hours involved in running a radiator shop. Some years went by where very little was accomplished on my two projects but I never gave up on them. The Chevy was my everyday car until about 1984 and the Ford has been on the road since about 1985.

In 2001 I began going to major swap-meets again after a long period of uninvolvement in any old car related activities. As I browsed through a Hemmings I realized that there was no one advertising the repair or recoring of heater cores for classic and antique cars. Knowing that many radiator shops across the country are closing their doors due to competition from auto parts stores and the perception that plastic tank radiators cannot be repaired I saw what I felt would be an increasing demand for an “old fashioned” radiator shop. There are many repair facilities that call themselves a radiator shop but all they do is sell new radiators and heater cores and don’t even have a torch anymore. Customers that live in rural areas may be hundreds of miles from anyone that can help them when it comes to an antique heater core.

The answer to that problem is Classic Heaters. If you can get to a post office, UPS location or any pack-n-ship store we can help you. As parts manufacturers discontinue production of parts for the older cars we will fill the need for personalized service in this specialized area of the classic and antique car hobby.

Cap a Radiator /Classic Heaters

994 Fulton Street

Farmingdale, NY 11735

Phone: (516) 293-9026

Contact Us

Address: 994 Fulton St. (Rt.109), Farmingdale NY 11735

Phone: (516) 293-9026

Email: [email protected]