Welcome to the BugShop FAQ

The text following is part of a series of articles written by John S. Henry on the restoration and maintenance of air-cooled Volkswagens. While his experience is exclusively with the Beetle, many of the techniques can be applied to other models.

This text is copyrighted and duplication, re-distribution or publication is prohibited without consent of the author.

Article: Heating your Beetle
Last updated: 10/30/01

Heating your Beetle

Symptom: You are cold in the winter; your girlfriend/wife doesn't want to ride in "that" car; you are no longer amused by the ice crystals that form on the inside of the windshield when you breathe on it.

This is probably one of the most often asked questions about bugs and it aggravates me. It aggravates me because sometimes I hear really stupid advice from people who live in areas where they don't even need heat. And I get just a bit aggravated when I hear people comment "Beetles don't have heat, do they?". I drove my '68 winter beater for four years in northern New England. This period included the winter of '94-'95 which during the entire month of January, where I live, the temperature never got above 32 degrees (F) day or night. I performed the same modification to 3 of the Beetles that I drove over 13 years, and it was always adequate, even in the northeast.

A Primer on VW heat

 Prior to doing anything with your car, you must understand the dynamics of the heating system in the Beetle. Most of the air output from the fan housing is directed down through the engine cylinders, heads, etc. to keep the engine cool. But in the 40hp and newer ('61 and up) engines some is ducted out of the housing through those little "arms" (that what they always looked like to me) in the front of the fan housing. These were known as the "fresh air" systems. Via the 2" hoses attached, air is blown from these ducts through the heater boxes. Heater boxes are simply housings around the exhaust pipe that connects the exhaust ports from your front most cylinders to the muffler. The pipe inside housings have big, fat fins on them to allow good heat transfer. These heat up really fast. The hot air leaving the boxes is routed by the heater control box which is the little "head" on the back of the heater box with the lever that the heater control cable connects to. When the heat is off, the hot air is just routed out underneath the car. The heater box is part of the cooling system for your engine. Even if you never want heat in your car, you should keep those hoses from the fan shroud in place to keep air flowing through the heater box (or replace the boxes with "J" pipes). Without this, your engine may run hot and you may have warping problems as your heads heat up. When the heater control flaps are open, hot air is ducted into the passenger compartment under the back seat and into the heater channels to the front of the car. It comes out on the floor in the front and is also ducted up to the windshield via hoses inside the A-pillars. Keep in mind that the volume of hot air that is blown into the car is dependent on the fan in the fan shroud, which is dependent on the engine RPM.

 In case you are interested, the '60 and older engines had what is referred to a "stale" air systems. Many who have these engines and depend on them for heat would call them "smelly" or "oily" air systems. This is because the some of the same air that was used to cool the engine cylinders and heads was also ducted into the passenger compartment when the heater flaps were open. This was fine for the first few hundred miles of the engine's life after which it got oily and smelly, especially when hot. These earlier heat exchangers essentially used "J" pipes (fin-less, straight pipes from the forward exhaust ports) and didn't tap the hot exhaust manifolds for heat. While the heat from them was weak compared to the newer designs, a good pair of 36 hp heat exchangers fetches a good dollar these days.

 That is how it is all SUPPOSED to work.

Problems with heat

With this knowledge you should now be able to follow this air path and check out the entire system. This article is about FIRST insuring that the stock system, at least to where it enters the passenger compartment, is in proper working order. To that end, the following list leads you through the steps.

  1. Engine compartment seal. May sound unrelated, but this is a key component of the overall air flow mechanism in the Beetle ("air cooled", remember?). The seal around the engine should be intact and in place and sealing between the body and cylinder shrouds and breast plate (the sheetmetal that covers the muffler from above and goes down under the pulley). There is also a seal that goes over the back of the engine/tranny area and is attached to the bottom edge of the firewall. The idea is that the air above the engine should be totally separated from the air below the engine. One interior heat related consequence of poor engine sealing is that dusty, dirty, hot "road" air will be drawn up into the fan housing intake and eventually end up inside the car.

  3. "Fresh air" hoses. These are the cardboard or foil 2" hoses that connect the fan housing outlets ("arms") to the heater boxes. In later model VWs, they connect to sleeves which go into softball sized housings on the muffler, which are hose clamped to the heater boxes. Make sure that this fresh air path is solid, sealed and secured with hose clamps.

  5. Heater boxes. These are known to rust out and/or get really oily. If they are rusted, replace them, if they are solid but oily and dirty, take them out and clean them out. A good idea is to take them to the self serve car wash and blast them out with the high pressure washer. While they are out, make sure that the heater control boxes work smoothly. Make sure the flaps close all the way, otherwise you will get heat when it is 90 degrees outside in the summer. Also make sure that the cables are attached (duh!!) and they open the flaps all the way. I have seen replacement heater control boxes available but have never had experience replacing them. The heater boxes (control boxes included) are cheap enough, I would recommend just replacing the whole thing. Lastly, as you reassemble, make sure your exhaust connections are good. Use new gaskets at the head and a new "doughnut" gasket and clamp at the muffler. Don't be cheap, exhaust leaks can easily get sucked into the heat system and wind up inside the car.

  7. Heater hoses. These are the plastic, insulated, flexible hoses that connect the heater boxes to the body inlets under the back seat. The should be solid, not cracked or warped and well clamped. Replacements are readily available.

Ok, if all of those things are up to snuff, you can assess the inside situation. Now, while this is where most of the heat is usually lost and simple modifications can circumvent those losses and even improve a perfectly operating system, judgment is called for. If you read my lengthy text on dealing with rust, you know you need to ask yourself some questions about what you want to do. And what you want to do should be in line with what you want to use your car for and how much money, tools, ambition, skills, patience, etc. that you have. If you are doing a vintage restoration on a cherry, old (in my book that's early 60s or older) original Beetle, I would say don't modify anything (if it is really cherry and old, you should only be driving it on nice, sunny, warm days anyway). Make it "stock as a rock", and live with the heat the car was meant to provide. This may of course may require heater channel replacements which are not for the faint of heart (those are "#4" repairs, see the "General: Dealing with rust" article).

On the other hand, if you have to drive this car in any weather that might befall you, and it is not a vintage classic, and you don't have tons of money, tools, ambition, skills, patience, etc. then some moderate modification is in order.

My Modification

Hot VWs printed a letter that I sent them on this mod back in March (I think) of 1993. I for one will swear that the Beetle's stock heat exchanger output is adequate for any climate in the continental U.S. Will it match the heat output of a gas heater? No. But it WILL heat up the inside of your car in some damn cold weather.

  1. An airtight hood-to-body seal is essential. This is very often over looked. (an old blanket stuffed behind the dashboard will never work) This is sometimes difficult if you lower front body is not perfect. If your Beetle is not "showroom", you may need some home weather stripping glued with RTV to the hood edge, particularly under the bottom where the hood meets the apron. To test the seal's effectiveness, open your window a crack and feel for incoming cold air around the dash, gauges and glove box when your running down the highway. This creates a bit of a vacuum in your car's cabin and "invites" cold air in. If you detect air, go check out the seals again.



    A lot of air pressure is built up against the nose of the bug at highway speeds, and if it is cold air, you probably would like to keep it outside. No matter how much heat you can get inside the Type 1, it will be for naught if you have the arctic express blowing through your dashboard when you cruise down the road.

  3. Check your door seals. Easy one. Replacements are cheap, but you usually get what you pay for. $40 ones usually WILL last 4 times longer than $10 ones.

  5. Make an improvement to the way the hot air gets into the car. The tube inside the heater channel is almost never perfect, unless you've replaced yours, and it is only about 1 1/2" in diameter. Chances are, you are losing at least half of your heat to the cold exterior metal of the car. The solution is to remove the metal tubes under the back seat which route the heat into the heater channels (just break a couple spot welds) and port the flow directly into the passenger compartment using a 2 3/4" flexible fresh air hose. You can bring the hose through the old vent holes in the panel under the seat. I use a long hose that goes under the front seats, right to the front edge of the seat rails, since I rarely ever carry passengers in the back seat. You'll be amazed at the volume of hot air you get this way.



     JC Whitney sells 2 3/4" flexible duct hose for under $10. You'll want about 5 feet for each side. This is that black "fabric wound on wire spiral" stuff. It is very light an floppy. You can move it all around and stuff it under the rear seat in the summer when you don't need heat. This increase in duct size and decrease in length will more than double the amount of heat you get in the car.

  7. Oh, and you would like some heat up on the windshield too? I really wish I still had one of the cars I did this mod to, a picture would be very nice here (this requires a little more ambition and "handiness" but worked very well). Get a 2 speed blower out of a Super Beetle (behind the dash, black plastic housing, about 7" in dia.). Cut about a 3 1/2" round hole in the floor of the trunk just down from the fuse panel and mount the blower with it's intake opening over the hole (you'll have to be creative with your mount, stroll that hardware aisle at Home Depot). Create ducting to route the output of the blower to the windshield ducts (side and center, if you have them). In my '67 I used a 2-speed wiper switch from that same year to turn on the blower. This made it look pretty stock. The fan will draw the warm air that accumulates in the footwells and blow it up on the windshield. Again, this will take some ingenuity; I couldn't possibly tell you all of the details here, but it worked very nicely.



    I used another, similar implementation of this in my '67, but I didn't want to cut a hole under the dash. So I mounted the blower behind the speaker grill to the left of the speedometer so it could draw cabin air through the grill. I really think that a fan will draw much warmer air from under the dash than via the speaker grill, but with my '67, I couldn't bring myself to cut a big hole under the dash.

About Heater "Boosters"

 I am an electrical engineer and I can tell you that the electric "boosters" will never work. It is simple physics that says that you can never get enough energy out of you battery to generate enough heat to make a difference. A company that advertises in Hot VWs sells a range of boosters with their highest power unit consuming 960 watts of power from the car battery. Do the V=IR math and that's 80 amps of current at 12 volts. A stock VW generator refunds a max of 30 amps to your battery (360 watts), the after-market alternator conversions are 51 amps (maybe some higher ones avail.). How much heat is 960 watts? A standard drugstore hair dryer uses 1500-1600 watts. And by the way, it has been estimated that a 60 hp engine produces 2700 watts of power as heat.

See? Forget it.

My Experience with Fan Recirculators
[partially excerpted from the end of the BugMods! article]

In spite of my satisfaction with my documented heater improvements, I was always searching for ways to improve it further. The flow of air in the stock system works well when the engine is running at mid-hi revs, but at idle it may be less than adequate, even with my prescribed modifications. I was exploring ways to add electric fans to system to improve air flow. I had been "collecting" squirrel cage fans from Super Beetles for a few years, and had 4-5 of them. I first experimented with putting them under the back seat to "draw" air from the heater boxes when the RPMs were low. But that didn't work as the heat was pretty intense and these fans are made mostly out of plastic. This concept could work (and some parts companies sell such kits) if a metal squirrel cage fan were used and the motor was completely external to the fan and airflow. But be warned, these fans can be very noisy.

There is a company that does something similar with a kit that installs fans on the interior, under the back window and pushes air via hoses into the heater boxes. I didn't like this because:

  1. You were required to cut 2 big holes in the firewall behind the rear seat
  2. As a result, the engine noise in the interior would increase
  3. The fans are noisy on the inside of the car
  4. Your system would always "recirc" the air and never bring fresh air in the car. Sometimes good, but not always.

So I began exploring the idea of putting fans on the "cold" side of the heater box, invariably in the engine compartment. I mounted a fan on either side of the firewall, high up in the corners, and connected them to the input side of the heater boxes via a custom made "Y" pipes, so the fan housing could still contribute to the airflow when the engine was running. They were 2 speed fans and drew about 5 amps each on "high".

Did it work? Well, a little. Stuck in traffic in a snowstorm at idle, with the fans switched on high, I could feel a small increase in airflow if I put my hand in front of the hose end. But I took them out after a month or two. Not worth it, in my opinion.

About Gas Heaters

Today, I have no experience with gasoline heaters (I did get one in a '54 that I bought, but only had it for 2 weeks before somebody came and bought the whole car, heater and all, from me). For those that don't know, VW installed gas heaters in some cars. I'm pretty sure it was a dealer option. Two manufacturers that I know were used are Stewart-Warner and Eberspracher (sp?). And I am told that there is one place in the US that repairs/restores them. Those who use them swear by them. Instant heat, don't even need the engine running. But make sure you know what you are doing or consult with someone who does if you play around with one. They can be very dangerous.


Some of this borders on blasphemy of my "vintage" preachings. Namely, cutting a big hole under the dash. Please don't do that to a, say, '67 or older Beetle. If you do, don't tell me about it. The removal of the ducting under the back seat? Well that's not so bad. That could be replaced pretty easily. But I felt it valid to offer this because many people use Beetles year round as daily drivers.

So try those steps if you are so inclined. Get the hood seal tight, and do the floppy 2 3/4" hose thing. You know, one benefit of an aircooled is that the heat exchanger (heater box) begins producing heat almost immediately since the manifolds heat up after just seconds of running. Not true for a water cooled. I'm sure that if you take my suggestions a wear a sweater you'll be all right. I used to drive into New Hampshire or Vermont in my '68 to ski when the high for the day was a single digit, and always got second looks from passing drivers who once owned a Beetle who seem amazed that I was not wearing a coat, mittens and ear muffs.

Copyright© 1997; John S. Henry

[back to FAQ Index]