Just trying to get your thoughts on vent-free models. Is the ODS (oxygen depletion sensor) on these models enough for safety? They say that Carbon monoxide, nitrogen dioxide levels emitted from these units are safe. They also claim they are 99% efficient. I'm almost positive that if you installed a CO2 detector in the same room, it would surely sound. The vent free alliance just tells the consumer what they want to hear. Documented cases of CO2 poisoning are rarely heard of. Check out this link and post back with your thoughts. http://www.homeenergy.org/archive/hem.dis.anl.gov/eehem/98/980108.html

I consider unvented appliances as dangerous. I would rather have them labeled as U-Breathe-It.

A manufacturer would have to be insane to use a burner in a vented heater that emits more CO than the ones in a ventless appliance. Yet, the public is to worry about a cracked heat exchanger in a furnace and not to worry about venting the same combustion products directly into the room. Where are the legislator's heads at? Seemingly the dividing line is at the amount of fuel burned in the appliance. It is OK to have half or 1/3 the products of combustion of an ordinary furnace sent into the room, but not more - bah!

The legislator's heads are probably in a cloud of CO2. Currently there are 42 states that allow the installation of vent-free models. What's puzzling is they are not allowed in tight construction homes such as modulars and "unusually tight construction" I don't think the average homeowner would know how well the house was insulated, until a ventless heater was installed. It would suck all the Oxygen right from the room, and the ODS would kick-in. Cracking a window is no safe alternative for indoor air comfort.

I'm no expert on this subject, but I will post my experience with them.
I live in a well insulated house (I did the insulation when I built it). It is a tight house.
I have two ventless heaters inside. One a Dearborn and another of fire logs in my normally wood burning fireplace (with the damper closed), both have the ODS system, both are propane.
We have never had either one go off due to O2 problems. We do have 6 dogs living inside and they do require us to open and shut the external door more (exchange internal air?)than a non dog house would require.
I use these heaters for two reasons: 1)the dogs think it is the greatest to be in front of the Dearborn on a cold day and 2) my wife likes the looks of the fire logs burning. We also have central air and heat (three individual units, two down stairs and one upstairs)and use it if needed.
Our CO2 detector has never 'alerted'.
Yes,, we both sleep a bit more than we use to, but at 77 I think that may be normal, not due to the heaters. We have had them since I built the house in 1973.
I know that this does not make the heaters more safe and that to some I may be just a death waiting to happen, but I enjoy them and have faith in them. And an extra added attraction: electric heat in my situation is 1.49 the cost of propane. (by comparing the cost per BTU since both are almost 100% efficient.
There, for what it's worth.

It's not so puzzling when we realize that manufacturers of ventless combustion devices are liable in court if someone dies from not reading and obeying such a warning. As most new houses are sold to newbies in life, they won't have a clue that new houses are built tight, so the warning applies to EVERY new house built to code.

A ventless heater makes no more harmful combustion products than any of the condensing furnaces used, the difference is in the AMOUNT of exhaust, so the ventless units are reduced to no more than 30,000 btuh whereas many furnaces are twice that. Many states still prevent a unit over 10,000 btuh from use in a bathroom or bedroom because of the size of the room to the output.

The human mind is capable of being worried about bad combustion products from a chimney or direct-vent unit to the outside; but not worrying about the same combustion being vented INSIDE a small room at the same time.

www.heatpro.us energy businessmen's knowledge

Yes, you really have to find out the MAKE and MODEL to get good answers. There IS more than one machine made.