Carbon Monoxide (CO) can kill you. Many tragic deaths have occurred from it. The elimination half-life of CO is 4-6 hours, so steady exposure at significant levels will bind nearly all Hb (hemoglobin) to CO—after a time you die from lack of oxygen. Somewhere round 30 ppm becomes extremely dangerous (e.g. sleeping with that level or higher). Lower levels are not safe either and can be problematic (headaches and other side effects, greatly reduced mental and physical function)
There is the saying: “trust, but verify”. My advice as to safety is “don’t trust and verify first”.
I’ve been researching heating for my Sprinter photography adventure van, and I’ve concluded that a diesel heater is non functional for my purposes (won’t work at high altitude). It was down to 23°F inside my van a week ago in Yosemite at 9600' when that cold storm blew through.
I had turned to a propane catalytic heater marketed as being safe to 12000' / 3657m. On my current trip, one goal was to test the Camco Wave- @AMAZON3 catalytic propane heater. My test at 10200' elevation on the high setting showed a dangerous amount of CO being released, building up to 6 ppm within 20 minutes of use at the rear of the van, well away from the heater (7 ppm at about 6 feet away). The CO level would have climbed much higher with continued heating, but I was not keen on measuring the rate of buildup inside the van while making and eating dinner.
The next day, I tested two Camco Olympian catalytic propane heaters @AMAZON, the Camco Wave-3 @AMAZON and the Camco Wave-6 @AMAZON. Both emitted high levels of CO as measured about 5 inches above the heater using the CO Inspector Industrial by Sensorcon @AMAZON.
At 10,200', the Camco Wave-3 @AMAZON model was emitting up to 135 ppm CO at 5 inches or so above the heater. All that CO then dissipates into the van interior. A slightly open window (for fresh oxygen for the heater) does nothing to stop that buildup. CO is lighter than air and the CO is hot to start with, so a 'blanket' of CO builds up inside starting near the roof area. But even two feet below the roof, the level had reached 7 ppm within 20 minutes.
Additional tests at 6100' with both a Camco Wave-3 @AMAZON and Camco Wave-6 @AMAZON showed that both were emitting dangerously high CO levels on the high setting (low setting produced much less CO). It seems clear to me that these heaters cannot get enough oxygen to burn the propane properly when at their high settings at high altitude—and I do not consider 6100' high altitude since I spend nearly all my time in the mountains at 9000' and above, precisely where heat is needed the most starting in September.
Electric heat bypasses CO risks—I’ll be sticking with the Sprinter built-in engine heater and a 1500 watt space heater, the Aerus Apollo 2000 @AMAZON (claimed to do 1800 watts but but can really only do 1440 watts). It turns out that the Sprinter alternator can push out a whopping 120 amps at idle when a high load is present, so the space heater has minimal battery drain. Plus, the 5 kilowatt 400-amp Lithionics lithium battery can deliver 130 amps / 1600 watts for about 2.6 hours.
Water heaters, propane stoves, engines, etc all produce lots of CO. Idling the Sprinter engine with favorable wind conditions (wind blowing past the side and front of the van), carbon monoxide from the tailpipe infiltrated the cabin to the level of 4 ppm. I would say that idling any engine very long is a Very Bad Idea, particularly if wind might push exhaust around the van. Get a carbon monoxide detector and make sure this is not happening.
In testing, I also found that a cheap CO detector did work—eventually—it is very slow to respond whereas the CO Inspector Industrial by Sensorcon @AMAZON detects CO immediately.
Carbon monoxide detector
Playing Russian roulette with CO is foolish. It is why I went with a pro-grade carbon monoxide detector, the CO Inspector Industrial by Sensorcon @AMAZON. And I bought a 2nd one for my home so as to be able to diagnose any CO leaks near the water heater and/or kitchen.