Heat through cabin vents

Up here in Minnesota it can get QUITE cold, so I am always looking for more cabin heat. As a matter of fact I built the RV-7A while living in Las Vegas and I laughed at needing any heat. Now that I am in Minnesota I am planning to install a second heat muff so I can get as much hot air flowing into the cabin as possible. With just one heat muff and some REALLY cold OATs the cabin is just okay, if you have on all your cold weather gear, but not even close to toasty warm. With the heat coming out down by your feet it seems to keep my feet nice and toasty, but the cabin up by chest level is COLD!

So my plan for the 2nd heat muff is to route it up into the fresh air cabin vents (eyeball style) so that it can be aimed wherever I want the heat at the time and you can even adjust the flow volume (although I don't see much need for anything other than full blast this time of year). I was struggling with the idea of making a selector box under the panel for each vent so you can swap between cold air and hot air. For now I am just going to run the heat straight up to the vents, then twice a year I can swap which hose I hook up to the vents. I am hoping that this will heat the upper portion of the cabin up to a toasty warm state and the original heat muff will continue to keep the feet and area below the panel toasty warm. I shudder just thinking about what it would be like to fly with it Minnesota cold outside but nice and warm in the cabin, especially being able to aim those vents around, and maybe even put my hands in front of them every once in a while for a nice warm up!!

Has anybody done this before?? If so what kind of results did you get? Any advice or suggestions would be greatly appreciated!

Travis
RV-7A 45+ hours
Lake Elmo Airport

One of the things you can do to get rid of the cold is to block the holes in the rear baggage bulk head. That will stop a lot of the drafts and also put boots on the push tubes out to the wings. It will much warmer.

Norman CYYJ said:

One of the things you can do to get rid of the cold is to block the holes in the rear baggage bulk head. That will stop a lot of the drafts and also put boots on the push tubes out to the wings. It will much warmer.

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I have most of that under control pretty well, although I have some ideas for fine tuning it even more. The problem is that when its -15F you REALLY need two heat muffs to get the ambient cabin temp up to around anything tollerable for long flights.

Travis

Assuming you'll have a cable operated selector box to turn the heat on & off; I'd just run a pipe or two (tee'd) under the panel pointing horizontally, and let it go at that. Fittings on the ends are optional.

You're still going to have about the same amount of ducting anyway, and then you won't have to make yearly changes at the eyeball vents.

And should you need fresh air for some reason, you'll still have it.

I'm a heating/air conditioning contractor, and I just hate making changes to ductwork between winter and summer...

L.Adamson

Travis,

One recommendation I was given was to use 2" exhaust wrap on just the heat muff.

N941WR said:

Travis,

One recommendation I was given was to use 2" exhaust wrap on just the heat muff.

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What does it do? I think I have seen people who have wrapped their entire exhasut system, never understood what it was for. If you have any product info as well please post it.

Thanks,
Travis

Deven said:

I got behind on projects this fall and what you describe is about what I did. I only have one muff but it is plumbed to one eyeball vent after coming off the aft baffle. I haven't tested it to -15 but +15 is fine for me with warm clothes. I would like to build a selector box also but if I get behind again and feel the need for some air time its easy to pop the cowl and swap some scat tube.

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Well luckily I have only flown once at -15f, it was in November I think. It wasn't too bad in flight, but when I landed at a neighboring field to get fuel I sure wasn't too happy getting out to fuel up. I got feeling back in my fingers after a couple minutes back in the cabin, but man -15f is REALLY cold (did I mention I moved here from Las Vegas, previous to Las Vegas I lived in Tucson, and previous to that I lived in Phoenix). But I sure do love Minnesota!

Travis

Cabin Heat

Theres a company in Mn. that makes 4 into 1 exhausts. I talked to him at Oshkosh and he can spot weld studs to your exhaust pipe where your heat muff wraps around. This will give you more heat out of your present setup.
You should be able to find him on the internet.
If not I'll try contacting someone I know who had it done for his RV-7.
Gerry
7A N742GC

two heat muffs

I heard of some who install 2 heat muffs. If this would help, would you plumb them in series or parallel?

Bevan

Bevan said:

I heard of some who install 2 heat muffs. If this would help, would you plumb them in series or parallel?

Bevan

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Parallel, don't know that series would make as much of a difference.

I don't know which way works best, but I have
two heat muffs connected in series. I copied
my heat muff installation from two other RVs
that were connected the same way. I have
never opened the cabin heat over about 25%,
although I don't fly in very cold weather.

Tom

tomwebster said:

I don't know which way works best, but I have
two heat muffs connected in series. I copied
my heat muff installation from two other RVs
that were connected the same way. I have
never opened the cabin heat over about 25%,
although I don't fly in very cold weather.

Tom

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Something that comes to mind in a "series" installation, is that the heat transfer differential in the second muff isn't as great as the first; since the air has already been preheated to a higher temp.

However, I'd have to see actual test results between the two schemes, because the final output temp of the series might be higher than that coming from two parallel muffs. Yet the total btu output could be lower.............or perhaps higher ???

Two water heaters are plumbed in parallel or series, and plumbers always have different opinions to what is best.

L.Adamson

I have been flying off my phase 1 in cold temps. If the temp is 20-25 the heat is adequate. Below 20 it barely keeps things warm. I have been down to 10 degrees and it just keeps it tolerable with a warm jacket and jeans. Above 30 and it will make you sweat with it full open. Don

TravisHamblen said:

What does it do? I think I have seen people who have wrapped their entire exhasut system, never understood what it was for. If you have any product info as well please post it.

Thanks,
Travis

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On race cars and such the exhaust is wrapped to keep the exhaust from cooling until it exists the stack. This keeps the exhaust hot and helps pull it out of the pipes faster. It is an old racing trick.

In talking with Larry Vertterman you don't want to wrap his pipes as that can lead to corrosion.

However, wrapping just the heater muff helps keep the hot air in the muff and moving up to the cabin. That's the theory. I'm yet to try it but my friend with a -6 said it was the best thing he did. It is simple and not that expensive so even if it doesn't work, you are not out much.

I pick up my cabin heat from my oil-cooler outlet duct. It is up against the firewall, so I just put a piece of 2" tubing through the firewall and into the cooler duct. On the inside of the duct is a flapper valve which closes this tube off; it is hinged on the bottom so when opened it goes out and closses off the entire outlet of the duct and directs all of the cooler output into the cabin. There it divides into two ducts that are centered and just ahead of my feet, with the warm air flowing up over my body. The coldest whether I've flown in was +2C OAT, and I only had the heat valve slightly cracked. Its only problem is the oil doesn't warm up sufficiently until after takeoff. If you don't have a converging outlet duct on your oil cooler which turns the flow to the rear at the cowl outlet, you might consider adding one as it will cut your drag a little, plus serve as a good place to tap off a safe source of hot air!

oil cooler heat

ellipse,

Do you have any photos of your installation? I am to the point of getting the FWF kit (or parts at least) and have been considering the idea of using the oil cooler as a cabin heater. I've seen a few posts to this effect but no photos (I will keep searching the archives as well)

thanks,
greg

Vetterman mufflers--more heat

An expensive idea. I understand that L Vetterman makes mufflers for the RV aircraft which replace the two standard straight pipes, and they have heat muffs already on them. i talked to him about these mufflers for my RV-7 as i live up here in very frigid Canada. He claims that they make way more heat than the straight pipe setup, and with two muffs, you could tie the second into your vents. Holy would that be nice and warm. I believe he said it was around the 500 dollar mark for the mufflers. Somebody correct me if I am wrong.

Jarvis