Air Supply to Cabin Heat

[rodsmith]

I have a Vetterman exhaust with heat muffs on both mufflers plumbed to a cabin heat box on each side of the firewall. I hate to rob cooling air to feed these. They need air flow all the time, not just when using cabin heat. I'm considering feeding them from NACA ducts on the side of the lower cowl. Just wondered if anyone has done this or if it sounds like a good idea.

[Nev]

NACA ducts sounds like a good idea.

Incidentally, I have 2 muff's as well. So far, when ambient is -2 to 10°c, I alternate between having one vent cracked slightly open, then closing it. Leaving it on gets too hot. I haven't used both of them for any length of time yet. The vents are between the rudder pedals. It pumps out so much hot air that my right foot and the front seat pax's left foot get quite hot. If there was a way to vent one to the rear cabin it'd be good, and I'd mount the other one slightly higher if I was doing it again.

[Rollie]

I put a naca vent in each side of the lower engine cowl and it works fine.

[rodsmith]

I mounted the heater boxes low enough in the corners, that they feed 2" scat tube under the flooring one terminating centrally in the front floor and one in the rear.

[TimTall]

I put a NACA duct on the underside of the cowl just forward of the cowl flaps. It’s routed through a single exhaust muff to the center of the firewall at about the same level as the pedals. Works great. Even in below freezing temps it only needs to opened a little bit. Lots of heat with a huge volume of air.

[Light&Sweet]

I have no practical knowledge on the subject. I was, for future reference, researching naca submerged ducts and their effectiveness. I have considered oil cooler heated-air for cabin heat using a naca duct inlet.

A rather technical discussion of naca ducts: http://cozyserenity.weebly.com/uploa...uct_design.pdf

Somewhere (?) I recall naca ducts being ineffective in some installations because of placement and/or lacking in ram air pressure at the outlet.

Sounds like the respondents here are doing well with them on the forward sidewall.

[Bcone1381]

Thanks for that study!

[mbaerobat]

I went old school and used external scoops mounted on the cowling. Plenty of airflow to get enough cabin heat.
Have flown comfortably in -20c temps.

[N204jh]

Question about this set up. Rod mentioned that the heat muff on the exhaust needs constant fresh cool air (makes sense so the underlying muffler doesn’t overheat). While you may provide fresh air via direct or naca duct, if the outlet valve is turned off, doesn’t that preclude fresh air flowing through the system? Or it there enough leakage to provide sufficient cooling?

Or do folks install a Y valve and vent the heat overboards if not into the cabin? Or am I way overthinking this?

[jaredyates]

Most of the heat boxes handle this for you. When the heat is off, it all flows into the cowl.

[Bcone1381]

This winter I determined that my left heat box delivered air thru a SCAT tube at 130-140 F.

To expand on what Jared says....When I shut off my heat, my heat box continues to fabricate hot to dump into the cowl area. I did not initially duct that air out. I've Trouble shot hot cowl issues. Now I duct that 140F hot air out of the cowl exit. I think it was circulating around in there. Two heat boxes making 140F hot air from on a hot summer day is something to think about. Winter is about over. I will deactivate one of my boxes soon.

[N204jh]

Brooks, how do you plane to duct the heat out of the cowl? Since there are only two scat connections to the heat muff, in and out. Are you thinking of doing a Y with the valve?