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Question DetailsAsked on 12/20/2013

are vent free fireplaces safe

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6 Answers


I presume you are referring to gas fireplaces. Electric ones present no fume or gas risk other than initial burnoff of chemicals from the "glow logs" during the first few uses, when they commonly stink and put out some noxious fumes. Wood, pellet, coal, white gas, fuel oil, kerosene devices and the like you would basically have to be suicidal (and love dark soot marks all over your house) to operate ventless.

Click on the Home > Fireplaces and Home > HVAC links (in Browse Projects at lower left) and you will find several prior questions like yours, with answers.

Basically, IF everything works fine AND your combustion is absolutely complete (all gas is fully burned) AND you do not run it for more than a few hours in a normal sized house with all doors open so the combustion gases can dissipate in a large volume, THEN you should see no ill effects.

If you google a search phrase like - ventless gas fireplaces - or - ventless gas heaters - you will find a number of articles on the subject. Basically, from what I have read it appears that the health research that has been done indicates a very substantial percentage of ventless gas heaters and gas fireplaces put out significant harmful gases, and that even relatively low levels of the nitrous compounds and carbon monoxide they produce under any but ideal conditions can cause respiratory, cardiac, and child developmental issues; and can potentially be very dangerous to infants due to the reduction in oxygen carrying capacity of the blood.

I am not normally one to fall for alarmist environmental claims, but between seeing the research and seeing the number of serious illnesses and deaths in our cold climate area every year due to use of ventless devices, I am firmly opposed to them and feel they should be banned for indoor use. In my opinion there is no excuse for taking the risk, particularly since the devices in almost all cases do NOT come with any sort of warning devices or shutoffs if they are putting out dangerous fumes, when it is not expensive to provide direct venting through a wall for a gas or wood burning stove or fireplace.

It's funny - many people would scream about the danger if someone proposed capping off the exhaust duct from their furnace and discharging the exhausst into their home, or disconnecting the exhaust vent and running their gas dryer to provide indoor heat, yet they accept unvented gas heaters and fireplaces. Why risk endangering yourself and your family?

The other factor that the manufacturers downplay vastly is the amount of moisture you are adding to the home - one of my earlier responses on ventless heaters gave the numbers - I think for a fair sized heater or fireplace it put out something like 7 gallons of water per 24 hours of operation into the household air, if I recall correctly. A good portion of that moisture ends up in the building materials and as condensation on walls and ceilings, creating the potential for mildew and mold, not to mention greatly increasing the incidence of "ghosting" on cold walls, where the air moisture condenses microscopically on the colder surfaces (typically around windows and aligned with studs and headers) and creates dark zones because it grabs onto the bonds the dust in the air preferentially at that location, obth due to the moist surface and due to the ionic attraction and binding ability of the moisture.

Answered 6 years ago by LCD


+1 to LCD's much more detailed and thorough answer.

In short, you would never catch me with one in my home. It flies in the face of all good sense and I don't care what the manufacturers say. If you are combusting something, prepare to have the associated and dangerous gases with that.

Hardly a candidate for a ventless application in my opinion and I don't know how these things are still legal.

Answered 6 years ago by WoWHomeSolutions


I for once may differ on opinion with the previous answers, and we mostoften give the same advice.

As long as you get one with the low oxygen sensor I feel you should not have anything to worry about. Many houses myself included have gas ranges in our kitchens and unless you are relying on the gas fireplace for your sole source of heat I would compare it to that. None of the gas ranges have low oxygen sensors and there are times such as Thanksgiving I have had a burners on the range as well as the oven going for well over 12 hours plus having my back up range in the basement going. I realize this is not an every day occurance but just an example of an extreme. Most all of the UL approved fireplaces have the sensors as far as I know and unless you are relying on it for your sole source of heat you should be fine. I would suggest buying a carbon monoxide alarm (wich you should have anyway) for each level of your home. The should not be too close to your fireplace, stove or furnace to avoid false alarms.

I happen to have one in my house and when Hurricane Sandy hit a few years ago it was a Godsend. I was without power for a week and I did rely on it for my only source of heat with no problems. The only electric on the one I have is a battery for the remote.

And as to the water given off. My humidifier runs almost non stop and there is no condensation on any windows or other places you would epect to see it. And as I used to build passive solar heated houses my insulation is supper tight. The out gassing of the different plastic products and oil based furnishings such as carpets and foam products produces far more.


Answered 6 years ago by ContractorDon


Hi, this is Meranda with Angie's List. Our Newsroom here has tackled this question in a few articles this year that I hope will be helpful in making your decision:

Are Ventless Fireplaces Safe?

How to choose between vented and ventless fireplaces

Good luck!


Answered 6 years ago by Meranda


No... vent free fireplaces are NOT SAFE. They are considered a health and safety risk by all state & federal healthy homes programs as well as the Building Performance Institute which oversees most state energy auditor programs..Many building codes prohibit gas vent free fireplaces and heating units.

Why? in spite of what the manufacturers literature may say- gas combustion will emit CO and excessive water vapor- even a low level CO below 30 ppm which will not trigger a CO alarm is unsafe, especially for young children. Excessive water vapor can cause mold & mildrew issues.

Answered 6 years ago by hosey


I respect what Don said, and he is right - in most cases a ventless heater or fireplace will not be a problem, ESPECIALLY if you only run if for a few hours at a time, and do not leave it running overnight. That is the most dangerous time, because carbon monoxide poisoning makes you drowsy, and eventually comatose at high concentrations - and people who are asleep commonly succomb to that effect before the headache and other side effects, so they blissfully sleep into death.

One thing to bear in mind - stated in previous comments, but I want to point this one safety item out - the safety shutoffs in all but a very few of the extremely pricey models are based on low oxygen level, NOT on carbon monoxide or carbon dioxide level. Generally speaking, depending to some extent of course on your ventilation and how the gases are settling by gravity in the building, one can get carbon monoxide poisoning and carbon dioxide suffocation long before the oxygen level drops. The oxygen sensors basically only work if there is a shortage of combustion air - say in a tightly sealed room. This sensor essentially prevents (assuming it works) the device from consuming enough of the oxygen in the room to cause you to pass out from lack of oxygen. Generally, a house has enough circulation of air between rooms to provide enough combustion air to keep the sensor from tripping off, but a device which is not operating perfectly can still turn out carbon monoxide (and carbon dioxide and nitrous oxides) in substantial amounts WITHOUT depleting the oxygen in a normal to "tight" house, so as Don said it is critical to have a carbon monoxide detector alarm on each floor. I also have a fancier one (about $45 versus $20-25) that shows the actual carbon monoxide level on a digital scale - very nice to have in a tight house or one using the furnace a lot (like in areas with true cold winters where the furnace is firing every 5 minutes or so), as it can indicate a rise in CO levels days before it reaches a dangerous or alarm level. And of course, best to use plug-in types with battery backup, so you are not trusting your life to just a 9V battery.

Answered 6 years ago by LCD

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