I think I'd call the guys at
http://www.portableheaterparts.com/contact.html

They have been quite helpfull to me in the past. Give them the specs on
your unit, they may have the right orifice on the shelf. Prices have
been fair. I'd be more comfortable with knowing I had the RIGHT orifice,
and that I wasn't overdriving the heater.

Bob Chilcoat wrote:

I've been converting a 150,000 BTU natural gas salamander heater to propane.
I finally got everything together Friday, and turned it on. Basically I
have produced an afterburner. Way too much gas flow -- sounds like an F-16.
BIG flame and it cycles on the overheat safety, not the thermostat.

OK, so I didn't calculate the resized orifices correctly. The jet block
consists of a cylindrical brass piece with ten radial #40 drill holes. I
machined a new one with #50 holes, based on the cross sectional area of the
holes and the relative heat content of natural gas vs. propane (because I
left the NG regulator inside, the pressure supplying this jet block is the
same as it was for NG). I figured that this would be a good first attempt.

Clearly not even close to the right size. I can deal with that, but there
is an interesting conundrum here. In trying to tame the flame, I throttled
it down with the propane tank valve, and got down to a more reasonable flame
size. For safety, I've put a CO detector in the garage during these
experiments, and with the BIG flame, it detects no CO. However, with the
throttled flame, the CO level rises fairly rapidly, and there is obviously
something in the air that strongly irritates the nose and throat.

I would have thought that the opposite would happen. The air flow is fixed
by the electric blower, so with too much gas there should be incomplete
combustion. There is quite a bit of yellow tips on the flames with the full
gas flow, which seems consistent with this hypothesis. However, with less
gas, there should be more complete combustion. There are fewer yellow
flames when I throttle back the gas flow, but I begin to get a lot of CO,
and that irritating byproduct.

Is my logic wrong here? I'm confused. With the gas throttled back, there
is very little yellow, the heater cycles on the thermostat, not the safety
cutout, and all seems fine except that it's trying to kill me. Thoughts
from you experts?