I have my heater unit high in the passenger footwell. As the rad is up front it becomes a bit difficult to get fresh air to the heater. Options would appear to be running a duct to:

1. A wheel arch - but I don't like the idea of all the road muck going into the heater.
2. Through the floor
3. Right up front with the rad - but it is a long way and the front section hinge makes it awkward.

What do most people do?

Possibly silly thought, but do you really need fresh air input directly to the heater unit, or could you get away with "recirculation" of the existing air in the cabin, and then add some other form of fresh-air ventilation to the cabin (that doesnt involve awkward ducting) to prevent condensation build-up?
Cheers
Richard

How about a NACA duct high up on the bonnet central or off to one side depending where the heater intake is? Thesed are supposed to be low drag but efficient air collecters and they lok pretty cool. someone on ebay does mouldings so you only have to cut out and glass in!

Caber

Helicopter vents will probably give enough air while on the move but I think that fresh air to the heater is vital in a middy - ask any Ultima driver how hot the car gets in traffic. Also, condensation is more of a problem when the car isn't moving so it will help combat this problem too.

A NACA duct would indeed be the best form of intake but as the rad vent is on top, the available airflow will be hot and therefore unusable. Also, the front section hinges upwards, so any ducting would have to move with it, making it impractical.

Have the pipe fixed in place so the duct drops onto it when the bonnet closes instead of stretching the pipe to follow it. Intercoolers and pollen filters use this method so it must be adaptable to an intake for a heater.

GTM Libra's use this method too - the hole in the bonnet meets with the intake duct as the bonnet closes. The duct seals against the underside of the bonnet using car door rubber. It worked reasonably well on mine, but the contours of the duct need to be well matched the underside of the bonnet, so it depends on how curve you're design is...

Gary

Thanks guys, I hadn't thought of that. I'll do some experimenting and see what happens

You didn't say what type of windscreen you have, but how about putting the inlet right at the base of the windscreen? There is high pressure there where the airflow stagnates.

There is very little space between the full windscreen and the top of the front section so a vent up there is not going to be easy - it would spoil the bodyline anyway.
I might be able to run an 80mm duct up to the rad intake. As the opening is slightly wider than the rad I think it will just squeeze in, picking up clean cold air. Most of the duct can be rigid plastic, with the last few inches in the 'concertina' stuff to allow it to hinge when opening the front section.