We've baan considering one of these for our future living quarters in thr building we're remodelling. I commented about it today to our town maintenance/gas supervisor/building inspector guy, and he said these aren't for use in well-sealed buildings, but rather garages, warehouses, etc. however, the ones sold at all the home-improvement stores have pictures showing them in dens, living rooms and such.
I'd wondered how these could work without causing carbon-monoxide poisoning, so is he correct?
If you read the instructions that come with a ventless heater they tell you exactly how, where and why to install a vent in the wall of your house to provide adequate air supply. The heaters all have an oxygen sensing system that will turn them off if any problems occur. A properly vented house will obviously be safer but will also reduce moisture buildup, the most common complaint that folks have about this type of heater.
I bought a 60,000 btu propane ventless heater and switched from a pellet stove to it this winter. I am completely in love with it. Instant heat, silent, worked when the snow knocked out power in the winter and no lugging bags of pellets around and cleaning up ashes. My house was built in 48 so it isn't exactly sealed. All I did to vent the house was to open the flue in the fireplace a bit.
Hey the carbon monoxide has to go somewhere...I think he's right.
By design, non-vented combustion heaters are going to exhaust their emissions into the room. I think that most of them sold today have some sort of CO cutoff switch built into the controls, but I can't verify that as a fact. Lots of local building codes ban them, but they may or may not be legal in your area regardless of what the pictures on the boxes show.
If they're used for a couple hours now and then for atmosphere in the room chances are they aren't going to be all that dangerous, but I wouldn't want to count on one for continuous heating.
Is your gas range vented? Where does all that CO go? Carbon monoxide is the result of incomplete combustion commonly due to malfunctioning heating equipment. Gas logs should not present a concern for occasional use. We use them frequently in the colder months and they are invaluable as a source of emergency heat.
We use non-vented natural gas logs in our fireplace as back-up heat. We also have a non-vented stove to keep our finished basement warm. All these units will shut-off if the oxygen content drops below 21%. If you have a concern about CO, just buy and install a battery operated CO detector.
The only complaint I have is that when you come in from outside you have that special odor that all these heaters emit. Don't notice it after a few minutes.
Check you local ordinances. Some areas ban them.
Any reason you can't use a vented unit? We use a rinnai, and are quite happy with it, only requires a small vent to the outside.
Don't do it!! We made that mistake when we enclosed our back porch and turned it into a family room.
The problem is not carbon monoxide, it is the other by-products of combustion. All the windows ended up with a film on them just like a heavy smoker lived there. The worst was the water vapor which buckled all the drywall that I had put up for the ceiling. I ended up having to tear it down ad redo it. And the problem wasn't from lack of insulation, I had put 18" of fiberglass in the ceiling.
After 3 years of that mess we junked the ventless and got a propane gas stove that has a double pipe (one inside the other) chimney. Air for combustion comes down the outer part and the by-products go back out the inner one. We hace had that stove for 10 years now with no problems.
I have used the propane versions with success . We used one for a couple of months without any problems. We also had two CO detectors at the time just to be on the safe side. Our house was fairly drafty so we never had any problems with moisture or fumes.
Knowing what I do now and in our present house, I wouldn't go that rout except as an emergency or supplemental source of heat when it's super cold outside.
In your shoes, I'd look into mini-split heat pumps. That's what I replaced the propane heat with. At the time it was around $800 off Ebay, now they are in the $1000 range. It worked great and with minimal brains you can install it yourself and just have the AC guy vacuum it down and open the valves, unless you happen to have a vacuum pump. 
Edit, I've installed two. The first was a 2 ton, 10 SEER. I ran it for 6 years and it developed a leak. I decided to update to a higher seer rating. I gave it to Curmudgeon to put in his, at the time, shop. I bought his house and got it back. It still works pretty good, but does have a slow leak. I switched it from R22 to R290 so I could charge it myself. It is a Klimaire.
The second is a1.5 ton, 21 SEER, with the variable speed compressor and fans. It was fairly pricy, $1800. I put it in three years ago. I still own it, in the rental house. It's a Harbor Point. It did burn up a compressor controller, out of warranty. The manufacturer replaced it for no charge and I installed it.
Both of these companies are Chinese, with distributors in Florida. Both of them were selling on Ebay.
Just to add some details:
1.) This won't be a primary heat source, mainly just for ambience. That said, never having lived in a house with a functioning fireplace, I can't guess how much use it might guess.
2.) We're pretty well insulated. R-39 in the ceilings, new windows with the casings insulated, new doors, etc. so condensation could be an issue.
3.) We probably wouldn't even be considering a ventless gas fireplace, but the people who owned the building before and started the remodel already had the gas line plumbed for it.
4.) We really don't want to deal with a vent through both the brand new ceiling and brand new roof, plus being a flat roof I don't want any potential leak points.
In those instances, I'd do it. Buy a couple of good CO detectors and rock on.
A vent free set
-should have no smell (if burning sufficiently)
-for new sets first time use burn on high (3hrs solid logs-4-5hrs for soft lighter weight logs) with windows opened or damper cracked not doing so you can prolong the stink.
-damper should be closed after the initial burn
its a Vent Free set with damper open you will loose at least 40% of your heat.
-should not have any soot on logs if they do have build-up make sure logs are placed in CORRECT order.
- vent free sets are a very good heat source
-have a carbon monoxide detector installed near by.
Vented Sets -just for looks -messy -not a heat source. At All -a waste of money
Wow, Zombie-turkey canoe... 
Make sure the one you buy is approved for install in your state. Most of the crap the big box stores sell is not. Just did a job where the homeowner bought all Moen Faucets and shower valves "sold exclusively by L....". When the store couldn't produce the required approval numbers, the inspector made me remove everything already installed. That was just faucets. Imagine how pissed the inspector is going to be if its a gas fired appliance that can kill you. Some of those things are legal in my state, but I have a philosophical issue with them and will not install them for my customers.
petegossett wrote: Wow, Zombie-turkey canoe...
Did someone edit out the SPAM link already, or is he just a really incompetent spammer? 
WildScotsRacing wrote:petegossett wrote: Wow, Zombie-turkey canoe...Did someone edit out the SPAM link already, or is he just a really incompetent spammer?
I was trying to figure that out too - it sure reads like a canoe, but with no link or even a business name it seems really weird.
Zombie canoe with a soul, Cool user name too!
In reply to tr8todd:I value your opinion as a master plumber highly in these matters, what are your issues? I am also considering one for part time use.
I'll just add that I have 2 ventless gas log sets in my house. We really only use them when its REALLY cold out and they work wonders. CO detectors are a must, although with the safety features built in it would take multiple failures for there to be an issue. Ours can get our large great room to 80+ in a very short time.
They do smell on the first burn of the year, just like a furnace does. My dad has a nicer looking set that works even better. His has a remote and a thermostat too, which I would suggest for the extra money.
I am going to have to look at one of these more carefully. I have a fireplace with a broken damper and I was going to replace it with a top mount one. And a new stainless steel rain cap. However if I put one of these log heaters on the fireplace and then capped the flue and sealed off the damper u get my fire place back and as a bonus mo more hauling wood and I get more heat.
I looked up the code in my state and it looks like they are legal with an inspection after the install.
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