Here are the specs as provided by the mfg. Wave 8
I have used these heaters for 3 years or so.
They do produce some moisture similar (or maybe a bit more) to any propane system.
We have always kept an upper vent or side window open to vent moisture and also to keep some airflow.
I did a little test the other day and closed all the roof vents and had a side window open a tad in the bedroom. With the heater on low I woke up and had moisture on the windshield. Outside temps between 42 and 53 degrees F.
The following nite we had similar outside conditions , I opend the kitchen roof vent a tad as well as the bedroom window. In the morning there was no condensation on the windshield.
We enjoy the lack of noise that the heater offers, but realize that there must be some be some venting to prevent moisture buildup.
There is no perfect system but the cat heater helps us when boondocking by using no electricity and being quiet.
By using common sense a catylitic heater can be an important piece of equipment for people not wanting to use a forced air heater all the time.