Heater

AK recommend using either a heater from a Mk2 VW Polo or the Heat3 heater available from CBS Online. The original design allowed 'fresh' air from the engine bay to be blown through the heater matrix and into the passenger compartment for warmth and/or on to the windscreen for demisting.

However, recent IVA requirements have said that air cannot be drawn from a source of potential pollution, so 'fresh' air can no longer be drawn from the engine bay.  Taking it from the passenger compartment is the most straightforward alternative. This requires either end of the squirrel cage fan on the Polo heater motor that sits in the engine bay to be blanked off and a 40mm (ish) port to be fitted in the blanking plate to feed air in from the passenger compartment  via some suitable ducting.

I want to be able to use the Cobra through the winter in a 'reasonable' level of comfort so I have decided to use the alternative Heat3 heater. It has a larger heater matrix than the Polo heater and has two fan motors rather than just the one.

AK say that this heater can be installed in a similar way to the Polo heater. But there are now four fan motor ends to be blanked off and air ducting to be installed. So I looked to see if anyone else had used the Heat3 heater previously  and how it had been installed, but with no success. So I had to come up with a plan.

I thought that rather than blank off all the fan ends, a more elegant option would be to build a box around the heater to seal the entire heater assembly from the engine bay. I could then put ports for the ducting into the box and into each of the foot wells and duct air from the foot wells into the heater box.

However  with the body separated from the chassis  I didn't know how much clearance there was between the bulkhead where the heater is mounted and the chassis cross member and clutch bell housing. So using bolt holes that secure the body to the chassis as a reference point, I marked the position of the cross member and bell housing in the engine bay. This showed that clearance for the heater box would not be a problem.

I cut the basic shape of the heater box out of a piece of 600mm x 600mm x 0.8mm aluminium sheet. This would produce a box that would place the the front of the heater matrix approx 35mm into the passenger compartment and would still allow the AK plenum to be used. (Although its width is a bit tight for the Heat3.)

Openings were then cut for the heater hoses, air ducting and electrical connections, and the aluminium was folded to form the box. 

Corners were created with 20mm x 20mm Ali right angle section riveted to the sheet and grommets and air duct ports fitted.

Provision was made for the heater to be fitted into the box with 150mm M8 bolts. There will be  6mm spacers top and bottom made from 8mm i.d. fuel hose. The air ducting was added at this stage because it looked interesting...!!

With the heater contained in a box, I need to ensure that it is accessible if it requires any maintenance in the future. If I use the AK heater plenum in the passenger compartment that will be sealed around the edges so there will be no access from inside the car. So I will fix the heater box in place by bolting it into rivnuts in the bulkhead and sitting it on a rubber seal. This should keep the IVA man happy that no pollutants will be getting into the box and will allow me to remove the box in future if necessary. So the opening in the bulkhead for the matrix is now cut out and rivnuts fitted for the mounting bolts.

Finally, prior to fitting the heater box and matrix, ports for the air ducting have been fitted into the tops of the drivers and passengers foot wells.

So after giving the heater box a coat of paint, the heater was fitted to it with the two M8 x 150mm bolts and spacers and a strip of a medium density self adhesive foam strip was added to the flange that mates to the bulkhead. This provides the seal between engine bay and passenger compartment. The heater box was then bolted to the bulkhead with M5 bolts and air ducting fitted between the ports in the heater box and those in the passenger and driver foot wells.

Whilst I am not tackling the air ducting in the passenger compartment yet, I will have two options for the plenum when I come to it. First is the AK supplied air box that, with a bit of a tap, fits around the Heat3 matrix. I can now use this as the main seal is around the heater box so an air tight seal around the plenum is not as important. The second is the plenum with four moulded outlets that came with the heater. But that's for another day and I'll have a think about that and make my mind up when I'm doing the interior.

AK supplied plenum

Plenum supplied with Heat3 heater.