What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

One or two air intakes for heat

jcarter

I'm New Here
I'm looking to install a second heat muff on my RV6A to increase the cabin heat. I live in the north and fly in the dead of winter. The current system with one muff is not sufficient and one of my worst flights involved me drinking out of a water bottle that had significant ice in it which formed during my 2 hour flight. In order to maximize heat gained in the cabin I'm wondering if it would be better to add a second air intake and make the second muff on a completely separate set of tubing all the way to the cabin OR if I should place a Y intersection (can be seen in the link below) just after the existing air intake before the existing heat muff and have one intake serving two heat muffs.

https://www.vansaircraft.com/cgi-bi...2&browse=heatvent&product=air-routing-devices

My theory is that I should have a second air intake because of the following. With the Y I would expect the incoming air volume to remain the same but the outgoing air to be hotter than it currently is due to the slower velocity through the muff. However as the air increases in temperature, it heats slower and thus I think the higher volume of cooler heat would effectively dump more joules of energy into the cabin and thus heat the cabin up better.

However, I believe (but don't know) that the exhaust temperature is in the thousands of degrees fahrenheit (is that number crazy?). If that is so, the decrease in heat transfer speed due to the warming of the intake air would be negligible since there is still a very large difference between a thousand and a hundred degrees. The Y would be a heck of a lot easier to install as well since I wouldn't need to create a new intake hole.

Thoughts? Suggestions?
 
I have two RV6A's. one has the standard single heater, one has two standard heaters - one for the pilot, and one for the passenger. Each has their own muffler heat muff, their own firewall penetration, and their own air supply from the baffles. The plane with two heaters has 4 times the heat.
 
What PA said. 2 heaters with separate firewall boxes. Go the extra mile and just do it - its a sure thing for more heat, and its there just waiting to be used. I have it planned for my plane and space set aside if I decide its needed. I also have oil cooler heat, but thats iffy in really cold climates because the vernaterm will limit oil flow and negate its usefulness.
 
Last edited:
Before you change anything, try wrapping just your heater muff, not your exhaust, with exhaust wrap from an auto parts store.

This will help keep the heat in your existing heater muff and may be enough for you.
 
My limited experience . . .

It is easy enough do do the experiment of two heat muffs in series before you undertake the task of another FW flap. I have one heat muff but the exhaust pipe inside has pin-fins welded to the pipe to enhance the heat transfer. I have flown in sub zero temps and it is sorta ok, but really sensitive to EGT's.

I did (1) insulate the external shell of the muff, (2) have pushrod seals for the ailerons, (3) restricted the heat flow to a 1" hole in the baffle. This provides some balance between total heat with high flow and temperature with lower flow.

More circulation within the muff will help collect more heat, but stuffing is not much good according to posts. Internal baffles that cause the air to zigzag, or spiral will help collect more exhaust pipe heat. Continental has a spiral flow baffle inside the muff. Even a few hose clamps with U shaped fins under them would greatly help heat transfer from the pipe.

Recently, I have sealed the spar gaps, but still have a cool draft at my armpit by the fuse. Not sure exactly where that comes from. Maybe the pleats in the back bulkhead wall, those leak too, or the aft corner of my tip-up.

I don't remember the poster but some Minnesota guys posted a good list some years ago. I think Alex Peterson was one, that listed all the leaks that were sealed. I use "site:vansairforce.com search1, search2" in google to search, it seem easier sometimes.

Good luck in your heat improvement project. Keep all posted with any data you get, and welcome aboard VAF!!
 
If you have a Vetterman crossover exhaust, you might consider contacting them about a muffler exhaust. I have their muffler system, and the cabin heat muff surrounds the muffler and is generally much larger than a standard heat muff. It puts so much heat in the cabin using only a single SCAT tube and one muffler shroud, that I cannot ever run the heat on full blast even on the coldest day (RV9A).
 
I have this "Y" tube configuration on my RV9. I do suggest connecting the straight end of the "Y" to the muff with the longest duct run to help balance the airflow. I do have the Vetterman exhaust/mufflers. I rarely have the heat knot more than 1/3 out on the coldest of days.
 
Stuff some steel wool (stainless type that is used for kitchen scrub pads) into the heat muff. Increases heat transfer. May not totally solve the problem but helps a lot. I have two individual heat muffs, both with the steel wool. Generally has worked ok down to subzero temps as long as I'm not descending with the power pulled back.
 
Before you dive too far into more plumbing, try making the existing heatmuff more efficient. Get a stainless steel pot scrubber and lightly pack it into the heat muff. This will have two effects:
- a significant increase in heat transfer to the cabin air
- slowing of the cabin air, again increasing cabin air temperature

If that does not work, I?d go with two heat muffs in series before adding another cabin heat box and such. You want higher temps, not more volume.

Carl
 
Heater

It is easy enough do do the experiment of two heat muffs in series before you undertake the task of another FW flap.

I did (1) insulate the external shell of the muff, (2) have pushrod seals for the ailerons,

Recently, I have sealed the spar gaps, but still have a cool draft at my armpit by the fuse. Not sure exactly where that comes from. Maybe the pleats in the back bulkhead wall, those leak too, or the aft corner of my tip-up.


Good luck in your heat improvement project. Keep all posted with any data you get, and welcome aboard VAF!!

+1 to the above

I installed a second muff in series with the first through a single heat box in my 7. I also wrapped the muffs with a titanium heat wrap (Amazon). They are both piped reverse flow (inlet at the rear). I get plenty of heat through the single box so far, down to -10C at altitude as long as I keep the engine working at 2400+ rpm. Once slowed down in the cct the heat drops off noticeably. I also installed bottom cushion seat heaters. More to soften the memory foam cushions, which are like cement in the cold, than for the heat but it sure adds to the comfort. Most of the first winter was with one muff and no seat heaters. Very much nicer now. Only starting my second winter with plane but happy with the heat so far.

Al
 
I used two heat muffs on my first RV8, but with slightly different plumbing. I had the two heat muffs plumbed in series, fed from a single scat hose off the back baffle. There was plenty of volume and the second muff was being fed with already heated air. Inside the cabin I used a couple Y fittings to split off air to the back seat - with their own butterfly shut offs. There was plenty of air coming out in 4 places (2 for the back seat) and it was plenty hot. We live in Ohio and my wife would frequently ask me to turn down the heat. My current RV8 only has one standard heat muff feeding the firewall shutoff, and its not nearly enough. My January project will be to try and correct that, which will be more difficult because I have the AWI exhaust and there are space constraints on the back of the engine.
 
Wow. This is a tremendous amount of good info. I'm leaning towards just biting the bullet and making the second air intake but I'm going to have to sit down and think about all the other ideas in this thread as well such as putting the muffs in series and the note about the Y needing to be placed in the right place to balance airflow. Thank you very much for all the data.
 
I recommend the two muffs in series. This was the recommendation from Robbins wings (the guy who makes the muffs for Vetterman) and has worked well for my 6. I am now pretty comfortable down to about 0* with two muffs in my 6, though I have gone to lengths to seal the cabin up. At 0* I still need a jacket though, so it's still not where I want it. I halted my efforts, as I will soon be flying a 10.

Be sure to carve out the inlet / outlet side of the muff that has the holes drilled. Both should be fully open, without restrictors, when used in series.

With separate inlets for each muff, you'll just get a larger volume of air that is not warm enough. Running in series will actually increase the temp of the incoming air.

Larry
 
Last edited:
If you have a Vetterman crossover exhaust, you might consider contacting them about a muffler exhaust. I have their muffler system, and the cabin heat muff surrounds the muffler and is generally much larger than a standard heat muff. It puts so much heat in the cabin using only a single SCAT tube and one muffler shroud, that I cannot ever run the heat on full blast even on the coldest day (RV9A).
^ My experience as well. This heat muff surrounds both crossover tubes, so there is very generous surface area for heat transfer. It's crazy effective!
 
Back
Top