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The unit measures about seven inches square. It has three doors that can be used to direct heat. The two round plastic plugs can be removed to plumb in the defroster pipe. The heater can be mounted in the center of the car, under the dash. We mounted it all the way to the right since it would not clear the glovebox in this particular car.
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The backside of the unit has three bolts for mounting and two copper pipes for the water hoses. An easy way to determine where to drill the mounting holes is to make a cardboard template with the holes cut out.
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Using the cardboard template, find a suitable place for mounting the heater. In this roadster, the cockpit's cowl brace was in the way. Instead of mounting the heater to the underside of the brace where it would hang too low in the footwell, we decided to modify the brace.
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In order to mount the heater up out of the way and against the firewall, we made a new brace out of 1x2-inch steel tubing. After welding the brace in place we cut an 8-inch wide section out of the existing cowl hoop to accommodate the header/defroster unit.
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Next we placed the template on the firewall, checked for overall fit and marked the holes where the heater hoses come though the firewall. Then we drilled the two water pipe holes and the two top mounting holes.
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After fitting the heater through the holes and were satisfied with the alignment, we bolted the heater in place. The bottom bolt came out below the firewall, so we used a 90-degree brace and mounted it through the top of the footbox, so the unit was secure and would not vibrate.
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On the engine side of the firewall, carefully measure and fit the heater hoses. Be sure to leave them long enough so they don't pinch. (If desired, a manual cable-controlled cutoff valve can be installed at this time).
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Now we are ready to work on the defroster pipes. These under-dash vents are out of an '87 to '93 Mustang and work well for this application. If you get these from a salvage yard, be sure to get the small piece of flexible hose that connects to each defroster pipe.
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Cut off the three protruding fins, so that the vent will fit flush under the dash.
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For the defroster ducting we used PVC plastic pipe. After measuring the required distances and checking for fit, we glued the pipe pieces together. We took one of the plastic plugs from the heater and cut a hole in it and fitted the plastic pipe through the hole, then reinstalled the plug in the side of the heater (see lower right area of photo).
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Here is the finished unit, painted black, ready to be installed. (No, you probably don't have to paint it, but we just felt better knowing that it looked good.)
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Next cut the cowl vents. Mark the area to be cut by holding the under-dash vents in place and marking the two bolt holes. Once the holes are drilled, then mark the slots and cut them out. (We used masking tape to protect the paint.) Ideally this install would be done before the car is painted and the windshield is installed.
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The finished holes should look like this. Use a chrome louver cover (available from Finish Line, it's called a "de-mist vent") to cover the hole and direct the hot air onto the windshield. When the dash is installed, wire the heater fan to a toggle switch, and the job is done.
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Here is the finished unit, tucked up out of the way, leaving plenty of foot and legroom. Wire the switchgear to a convenient spot and you'll be warm and toasty in no time.
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