Dual cabin heat?

Do most of you install one cabin heat box, or two? I've seen an RV-6 that had a cabin heat box coming off of each of the heat muffs on the left and right branches of the exhaust manifold. (It also had a third heat muff on the crossover tube for carb heat, but that's not germain to my question.)

The word from that owner was that two carb heat boxes was BARELY enough at altitude...and he had gone through the usual steps to seal the cabin against drafts.

I just installed one cabin heat box in the per-the-drawings location, i.e. just below the firewall recess. I'm trying to figure where -- if at all -- I should install the second one. I'm a little paranoid about just choosing a location only to find later that it interferes with something forward of the firewall. My firewall is presently bare.

Oh, one more question: what have you guys done about windshield defrosting, if anything?

Your opinions and suggestions, please?

Thanks,
Martin

mgomez said:

Oh, one more question: what have you guys done about windshield defrosting, if anything?

Click to expand...

While building my 7 I had left in wiring options so I could drive a defrost fan if it turned out to be necessary. However, my initial fanless effort worked well:

I used a bit of the 3/4"ish Vans plastic wiring/duct tube straight from the output of the heater valve (via a hole drilled next to the outlet vents by my feet). The duct then exits through the glareshield just behind the windshield.

While flying to Texas recently, I was able to see that just that little tube was enough to defrost my windshield by the time I reached the runup area. You can actually feel the warm air being pumped out by the windscreen.

So... no electric fan for me.

I have a tipup in Wisconsin. I just used the one standard heater. I haven't had any problems with the canopy fogging, but I haven't flown in any real rain yet either. I normally do not fly in temps below 20 deg F. The heater has been fine so far, using the Van's standard vent and heat muff.

Roberta

I have one standard heat muff from Larry Vetterman, and have never been cold in flight. I have gone on a 3 hour X/C in 10F weather. I wasn't toasty warm, but certainly wasn't cold.

How often (if ever) do you think you'll go flying in the cold AND dark? I don't think one heat muff would be sufficient for a 10F day without at least a little solar heating through the canopy.

I have an RV-8A. I only used one heat box on the firewall, but used two heat muffs. I plumbed the heat muffs so the outlet of the right heat muff goes to the inlet of the left. Works fine down to about 20 (above); below that it starts to get a little cool. I do have some work to do on canopy leaks, though, so it may get better when things are sealed up a little more.

The only problem I've had with windscreen fogging is on the ground in very cool, damp weather. Seem to clear up OK once you get moving. Figured I'd wait to do anything heroic about defrosting till I saw if it was going to be a problem. So far, not.

John Miller