All good questions and concerns ... thanks for all such comments, as it helps us figure out all aspects of both our choices and manufacturers' equipment. Our ventless heater brand, Mr Heater 30k btu blue flame models work great ... we've used them for years; safe, O2 sensor and cutoff, thermostat, etc. Vented models have a number of features that didn't work for us, such as complexity of installation, visible flame, and so on ...
But then I decided to monitor IAQ, with an eye to seeing if there were any undiscovered air quality problems from *any* sources ... if I found any, then I would address them in some form or fashion. Monitoring came first; this works, because I'm now seeing the results of our choices in other areas, and can now apply short- and long-term fixes.
Short-term fixes include just getting more air exchanges, by manually opening doors/windows ... the outside air is better (wrt CO2), and monitoring shows that it works. Problem solved, air quality rapidly improves. If you aren't monitoring (and who is?), and don't have automatic air exchanges by some other system (hvac of some kind), then just do the same opening/closing of doors & windows.
Other short-term fixes would be something that addresses the kinds of heating/cooking devices we have (ventless heaters, wood stoves, cooking appliances) ... now that I know there's a problem, based on our choice of these devices, we'll implement the fixes, as we find them. We *do* have a vent hood over the propane range, but we don't use it all the time ... we'll now test that, and hopefully solve the cooking issue of IAQ, w/o giving up cooking on gas,, which we love and would never give up. Thanks for that reminder!
Long-term, an automatic air exchange system of some kind seems the best way of ensuring we get air changes without lots of effort, and would also solve the winter problem ... just now looking into this, given that monitoring reveals problems.
Curiously, first monitoring, and then *research* into the results, reveals that CO2 *is* an IAQ problem, with health effects. I don't believe we can trust the old "1200ppm, 2000ppm, or higher levels" in homes, businesses, and subs are still "good enough per EPA and others"; I'm not sure I can trust a government or other agency that values business more than people. If outside air is 400ppm, then that is *my* target. We have CO alarms, but no direct monitoring yet of CO values ... good news is that our generator isn't in the house with us!
BTW, don't monitor, if you aren't ready to tackle what such monitoring might show ... that was our first mistake : )