Universal Replacement Car Heaters That Work

Reliable heat in your car may not fit neatly into Maslow’s hierarchy of needs, but it sure is nice to have when you’re facing yet another long, ice-cold commute, and the winter seems to stretch off into infinity. The problem is that some car heaters are prohibitively expensive to fix the right way, and most of the car heater alternatives out there are pretty anemic.

So what are you supposed to do if you can’t afford to pay a mechanic to tear out your entire dash to replace a busted heater core, or you drive an older vehicle with long-since obsoleted components and no new-old-stock in sight?

replacement car heater needed
No love for most car heater alternatives, but these actually work. PLASTICBOYSTUDIO / Moment / Getty

Universal Under-Dash and Auxiliary Car Heaters

If you find yourself in one of the situations outlined above, you can always try to get by with some kind of alternative 12V car heater, or just bundle up extra tight for your commute, but it doesn’t have to be that way.

There’s a broad class of products out there that are designed to essentially replace the heater system that your car came with a way that even the best 12V car heater can’t do. These devices are made up of two basic components, just like your factory heater system: a heater core and a blower motor.

The way that this type of replacement car heater works is that it has a heater core that you have to connect to your engine cooling system. In addition to the heater core, it also has a blower motor that has to be wired into your vehicle’s electrical system.

Once those connections are made, this type of device functions in exactly the same way that your factory heater used to. Hot coolant from the engine passes through the replacement heater, the blower motor forces air through the core, and warm air is expelled into the passenger compartment of your vehicle.

These heaters can fully replace your car or truck's factory heating system, but they have to be connected to your vehicle's cooling system to do so. If you aren't comfortable with that type of work, consult a trusted mechanic about installation costs before you buy one of these units.

The Best Options for Aftermarket Car Heaters

Some replacement car heaters are under-dash units that can look almost factory-installed if done right, while others are large, bulky units that are technically meant as auxiliary heaters for larger vehicles.

You can use either type in any vehicle, but you’ll need to pay attention to the size of the unit compared to the available space that you have, in addition to the amount of heat that any given unit is capable of putting out.

Maradyne H-400012 Santa Fe 12V Floor-Mount Heater

A Maradyne aftermarket replacement car heater.


Heat output: 12,200 BTU/hour
Fan: two-speed
Flow rate: 200 CFM
Current draw: 6A @ 12V

What We Like
  • Includes a built-in blower motor.

  • Decent flow rate.

What We Don't Like
  • Only two fan speeds.

  • Plastic construction lacks durability.

Maradyne’s H-400012 Santa Fe is a replacement car heater that contains both a heater core and a blower motor in one slick package. This is an example of a replacement car heater that is designed to be floor-mounted, and not look out of place, provided that the vehicle has black trim components.

In order to compare this type of replacement car heater with other alternatives, 1 BTU per hour is roughly equivalent to 0.29 watts. So with a heat output of 12,200 BTU per hour, this unit is comparable at a 3,538-watt heater.

That’s more than 10 times the wattage of any 12V heater you can plug into a cigarette lighter socket, and represents significantly more heat output than any battery-powered heater can put out.

Flex-a-lite 640 Heater

A Flex-A-Lite 640 Mojave Heater


Heat output: 12,000 BTU/hour
Fan: three-speed
Flow rate: 140 CFM
Current draw: 6A @ 12V

What We Like
  • Includes built-in blower motor.

  • Three speed fan.

What We Don't Like
  • Relatively small, but still too big for most passenger car applications.

Flex-a-lite’s Mojave 640 is another example of a replacement car heater that combines both a heater core and a blower motor into an attractive package that won’t look out of place in many vehicles.

This particular unit is designed for under-dash installation and has the dimensions for it, as the unit is only about 5 inches tall. It's still too big for some passenger car applications, but you can take a look and see if it might fit in your vehicle.

JEGS Hot Rod Heaters

JEGS hot rod heater

JEGS High Performance

Heat output: 12,000 - 40,000 BTU/hour
Fan: three-speed
Flow rate: 170 - 300 CFM
Current draw: 4.9 - 11.6A

What We Like
  • Puts out a lot of heat.

  • Built-in blower motor.

  • Three speed fan.

What We Don't Like
  • Too big for some applications.

JEGS Hot Rod Heaters can be used as a replacement or auxiliary heaters, and they run the gamut from similar in output to the Maradyne and Flexalite units to significantly more heat output.

The largest JEGS heater puts out 40,000 BTU/hour, which translates to 11,600 watts. Your typical residential heater will top out at 1,500 watts, so that’s a lot of heat.

How to Install a Replacement Car or Truck Heater

As you might expect, installing one of these universal floor mount or under-dash car heaters isn’t as easy as installing an electric car heater. Some electric car heaters are tremendously easy to install, like cigarette lighter heaters that are literally plug-and-play. Plug them in, and you get warm. Others require a little bit of wiring.

In order to install one of these true replacement units, you have to do electrical wiring and also plumb the heater into your cooling system. That means you have to either get to the holes in the firewall that your existing heater core uses or punch new holes.

If your problem is that the heater core is too time-consuming, and thus expensive, to reach you or your mechanic will have to put new holes in the firewall. Careful positioning of such holes is extremely important to avoid damaging anything, and the holes need to be properly insulated to avoid harmful fumes entering the passenger compartment.

Once you have access to holes through the firewall, the next step is to tap into the engine cooling system.

You can use the existing heater hoses that were connected to your busted heater core if you’re bypassing it, or you can splice and tap into a heater hose if you’re installing one of these units as an auxiliary heater.

If your existing heater core is plugged, consider bypassing it. Tapping into a heater hose that leads to a plugged heater core will prevent your replacement heater from working.

In either case, it’s important to note the direction of flow through the cooling system so that you connect the right hoses to the inlet and outlet of the replacement heater.

With the heater connected to the cooling system, you have to wire the blower into your vehicle’s electrical system. If there is room on the fuse block, you can go that route. If there isn’t, then you’ll have to run a new wire through the firewall to your battery with an inline fuse.

You’ll also need to make note of the amperage that the blower is designed to draw and use an appropriate gauge wire and fuse

Can a Replacement Car Heater Really Replace the Factory System?

Unlike most alternative car heater options, products like the ones we looked at here can absolutely replace a factory heater if your bad heater core is too expensive to fix the right way, or you drive an older vehicle and are having trouble finding compatible parts.

Some units put out more heat than others, but even replacement heaters on the lower end of the scale provide significantly more heat than any 12V heater you’ll find.

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