I thought I'd follow up with some results. I ended up with a red dragon
propane heater that I bought off ebay for around $250.00 including
shipping. I think the new ones are around $550.00. The nice thing
about buying used off ebay is that if I am unhappy with the item I can
always sell it and not lose too much money. I used the red dragon
twice. Both times outdoor air temperatures were around 20F. I did not
use any blanket over the cowling because I wanted to measure
temperatures while the heater was running. In the future, probably not
until next winter, I'll use an old sleeping bag on top of the cowling to
help retain the heat. The highest surface temperature on top of the
cowling I measured was about 170F. Next winter, I plan to take more
measurements inside the cowling - cylinder heads, oil pan, etc.

The red dragon did a great job. No problems with moisture. I've had
condensation problems using the propane heater in my garage. Tons of
moisture collecting on cold steel hand tools. I suppose the difference
with the airplane is that after a few minutes, there aren't any cold
surfaces under the cowling so the moisture can't condense anywhere. I
let the heater run for about 20 minutes and my IO-470 started right up.
I forgot to check the oil temperature so I don't know what is was
before starting. By the time I looked at it it was already in the green.

I ran the 12Volt blower from my car battery not the airplane. My first
test next winter will be to run the blower off the airplane battery and
see how much battery capacity I lose. I understand that the blower uses
4 amps at 12 volts so running it for twenty minutes should leave enough
capacity for cranking but I'd like to make sure of that on a cold day at
my hanger not at a remote location. No use warming up the engine and
being left with a dead battery. I hand propped a cub a few times. I
don't think I'd want to try that on the bonanza.

On my last airplane, a citabria, I had a pan heater that if left on for
4 hours or so did a great job. On the io-470, if I went the 120 volt
electric heating route, I'd probably go for the full Rieff or Tanis
setup costing around $1500-2000 installed - I think. The two problems
with the 120V arrangement is the need to turn it on several hours before
starting and the possibility of being at a remote strip with no access
to 120V power. All things considered, for my purposes, I prefer the
red dragon. One more pirep, I had a question about the heater so I
called the manufacturer, Flame Engineering. They were a pleasure to
deal with.
Dave
Bonanza M35


dave wrote:
Another thread made me think about using the portable propane heater I
use in my garage to preheat my airplane. It's the standard metal tube
type with the fan from Home Depot or Lowes. I've seen people simply
attach a flex duct to the end of this type heater and blow the hot air
into the cabin - poor man's red dragon. Any drawbacks?
Thanks
Dave