I'm late to the discussion but I have a Wave 3 in my 6x10 cargo conversion and I was interested in just what happens during the operation of this heater.
I tested the Wave 3 in this trailer with a BW Honeywell 4 gas detector and found that with all trailer vents shut and doors closed (just for a control test, never to be operated like this in service!) and within 20 minutes the interior O2 percentage reduced from the ambient 20.9% to 20.4% (the alarm threshold defaults a 19.5%), but it seemed to stabilize there and go no lower. Presumably the cumulative imperfections in air tightness of doors and other things like the A/C access hole provided air exchange sufficient to maintain this stasis. With ceiling vent cracked open and floor vent opened, the percentage quickly resumed the 20.9% of the outside air and never wavered from this figure, heater operating all the while.
The heater is claimed to discharge CO2 and water vapor (like our breath). With vents closed the windows did become fogged, and with venting restored the fogging was much reduced but still a bit apparent. The detector did not register any CO gas presence within the scope of that test.
The heaters' included directions strongly encourage the owner to protect the unit from dust and to employ a dust cover such as they sell, when dusty conditions are to be encountered. (personally I think they ought to supply a dust cover with the heater rather than as a separately sold option!)
From the results of my ad hoc test and the fact that one can find plenty of instances where people are heating camperised vans (that have an interior volume little larger than that of a crew cab pickup truck) with this device and we aren't hearing of people being slaughtered around the country as a result, it would seem that for a prudent person the Wave 3 is not a bad choice of small trailer heater. I have used mine for 2 years so far and I'm quite satisfied with it. I believe that air wise, a properly operating Wave 3 is the equivalent of having 2 or 3 extra people breathing in the enclosed space you would share.*
* years ago I made a 100 mile evening trip to another city in a car with three other people, and the heater in that Buick Riviera was not working, cold air only. It was late fall and cold out and for comfort I left the defrost fan on low so not to blast cold air on the occupants. With four people breathing in that closed space the amount of water vapour accreting on the windows was amazing, I had to blast the fan on high every few minutes in order to clear the inner windshield so I could see. Based on the rate of fogging I observed in the vents-closed cargo trailer, I'd have been better off water vapour wise with just me and a Wave 3 in that car!
You can't go wrong playing it safe, and I won't fault those who advise caution to an extreme, but in my experience a properly vented and reasonably protected Wave 3 is a good and practical way to get the chill off during cold times in a trailer or van. Works for me.
