Peter

I had the same concern with respect to wasting valuable head pressure in the plenum.  I compromised since I did not want to stress the exhaust.  What I did was add some scat to the exit of the heater valve which was mounted at the lower end of the firewall. I chocked the scat into a duckbill which should maintain back pressure but with enough of a gap (3/8 inch) to allow cooling air to pass over the exhaust in the heat exchanger.  I don't see any evidence of significant heating on the exhaust down tube inside the exchanger or the cylinder head

Thanks

Tom

Sent from my iPad

On Feb 2, 2012, at 8:49 AM, Peter Sokolowski <air.peter@googlemail.com> wrote:

> I am routing my cabin heat hoses and the follwoing was braought to my attention.
>  
> Presently I take the pressured air from my plenum, than to the heat exchanger mounted on the exhaust and routing the heated air to the valve which I can open for cabin heat or close it. If I close it, the air gets blocked at the valve as I thought it is better to block it rather to dump the heated air to the cowling. Reason for that is that I get the air from the plenum and dumping it to the plenum reduces the available air to cool the engine and reduces the pressure difference between the plenum and the cowling.
>  
> Now a friend mentioned that I might get a heat blocking at the heat exchanger with undefined consequences. So to say better dump the air to the cowling rather than getting a cracked exhaust.
>  
> What is your experience / opinion ?
>  
> Thanks in advance,
>  
> Peter
> D-EPSO, LNC 360 MKII (95%)