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Avoid Unvented Gas Heaters

Posted on Sep 23 2009 by Alex Wilson

Let me get right to the point: unvented gas (and kerosene) space heaters and fireplaces are a bad idea. Don’t install one.

Euphemistically called “vent-free appliances” by the gas industry (see, unvented heaters and fireplaces that are installed indoors release combustion products directly into the living space. These heaters are very popular, with buyers attracted to the low purchase price and inexpensive installation. According to data in Appliance Magazine, U.S. sales of vent-free room heaters have averaged 290,000 units per year from 2004 through 2008.

Installation is cheap. You just buy the unit, hook it up to your gas supply, and turn it on. There’s no annoying vent pipe to install through the wall or up the chimney. Simple, right?

To dig a little deeper, let’s take a look at combustion. When we burn a hydrocarbon fuel, such as natural gas or propane, the fuel reacts with oxygen producing heat and two primary combustion products: water vapor and carbon dioxide.

Using your living room as a chimney

There are two problems when we allow those combustion products be exhausted into our living room.

The first is that, along with water vapor and carbon dioxide, there are some combustion by-products that aren’t good for us. With an unvented gas space heater, the combustion process is very complete — 99.9% efficiency or higher, according to manufacturers — but that tenth or hundredth of a percent can be pretty nasty, containing constituents as carbon monoxide, nitrogen dioxide, soot, and unburned hydrocarbons.

Carbon monoxide is toxic (even deadly) at high levels and causes long-term health problems at low levels. Nitrogen dioxide, at even minute levels, may affect our immune systems and increase our susceptibility to respiratory infections. An oxygen depletion sensor (ODS) on unvented gas heaters and fireplaces shuts off the gas flow if the oxygen level drops below 18% (an indicator that not enough fresh air is getting into the house), but the ODS does not detect carbon monoxide or other hazardous emissions.

The second problem with venting combustion products indoors is that even the “clean” combustion products aren’t so good to introduce into our homes in large quantities. High levels of carbon dioxide make us feel drowsy and may cause eye irritation. Large quantities of water vapor released into our houses will raise the humidity level and can result in condensation on windows, concrete slabs, or areas of wall with “thermal bridges” through them. This moisture can result in mold growth, induce allergies and asthma among homeowners, and cause rot. The tighter the house, the greater the risk. A 30,000 BtuBritish thermal unit, the amount of heat required to raise one pound of water (about a pint) one degree Fahrenheit in temperature—about the heat content of one wooden kitchen match. One Btu is equivalent to 0.293 watt-hours or 1,055 joules. /hour unvented gas heater will produce about a third of a gallon of water per hour — about seven gallons per day if operated around the clock.

One should get an inkling that unvented gas heaters and fireplaces aren’t so good by reading the warning labels that come with them — suggesting that a window be opened during operation, that they not be operated for more than four hours at a time, and that they not be used as a primary heating system. Are those recommendations really going to be followed?

That unvented gas and kerosene appliances are a bad idea is no secret. A lot of scientists and health professionals have long argued that they don’t make sense. Our publication, Environmental Building News, and other publications such as Energy Design Update and Home Energy have argued for years that such appliances should, in fact, be banned by building codes.

But, remarkably, the regulations have gone the other way. Strong influence by industry in the code-setting process and the adoption of increasingly universal building codes have made it more and more difficult for states and provinces to prohibit these products. The International Mechanical Code accepts unvented heating products, and that code has been almost universally adopted throughout North America. In 1996, six states prohibited these unvented heaters (California, Alaska, Montana, Minnesota, New York, and Massachusetts), as did all Canadian provinces except Manitoba and British Columbia. Today, they are prohibited in only one state: California.

Even though we are largely blocked from banning unvented heating appliances through our regulations, we can at least exercise our good sense by not buying them. It’s more expensive, but we should only install combustion heating equipment that vents to the exterior. Period. End of story.

I invite you to share your comments on this blog. You can also follow my musings on Twitter.

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Thu, 09/24/2009 - 11:11

unvented heaters
by Catherine Silver

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You WILL experience a residue all over your house if you run an unvented heater. We supplemented our radiant heat system running the unvented heater periodically in the cooler side to our house in the kitchen to try to offset the higher gas costs of last year, but it isn't worth it. I will be removing the unvented heater. Even with the window slightly cracked I had a film on all glass window surfaces- so you know it is everywhere. Thanks for posting this article.
(On another note- Our radiant system was a retrofit situation- I don't recommend it under certain existing floors. It is excellent in the concrete pours but far less efficient under existing floors )

Sat, 10/03/2009 - 14:15

by Perry Bumpers

Helpful? -1

You are right on target with your informatiom about ventfree [ ROOMVENTED PRODUCTS] It does not matter if it is a ventfree log , space heater or ventfree fireplace. The results are the same when a ventfree product is used to heat with . Bad smell ,water running down windows & walls, discolored walls & celings. SOOT SOOT & more SOOT [soot is very common with ventfree logs and fireplaces ]. People complaining with more headakes , sinus problems ,colds sore throats. The list just goes on and own. Most information that the consumer is given about ventfree is incorrect. They are made to belive they can use the ROOMVENTED HEATER , LOG. OR FIREPLACE TO HEAT THERE HOME WITH. All the consumer is told is 99.9% of you heat comes in the room. You loose no heat up you flue. Heat for pennies a day. Save big $$$$ heating with ventfree products. It always about the heat. Hardly anyone that sells a ventfree [ ROOMVENTED] product makes the customer aware of sizeing guidelines for ventfree products. That they should be used no more than 2 to 4 hrs in a 24 hr period. Never to be used as primary heat suppliment only. That you must provide proper combustion & ventalition air. New tight build homes may require 2 windows open to provide enought combustion air. This is not a concern when a directvent fireplace insert or stove is used. The air for combustion comes from out side you home. Vent free products burns up the good air in the home and dumps the trash out in the room where your family lives. YOU LIVE IN YOU FIREPLACE WHEN YOU USE A VENTFREE IN YOUR HOME. Probably 75% of all ventfree products sold are to large fo the room they were installed in. There are 1000's of homes that have a window A/C unit & a ventfree product of some type that is there only heat source. EVEN THOUGH VENTFREE IS NEVER SUPPOSE TO BE SOLD OR INSTALLED FOR PRIMARY HEAT. Do your research you may have to go around the world to get the correct info . usually some where other than the gas company or the person selling ventfree products. GOOGLE DANGERS OF VENTFREE. You will have to dig a little but some good info there. I have been in the hearth industry for over 20 years now. I would never sell my customers a ventfree product . I would never put a ventfree in my own home. Sure I could have jumped on the band wagon made some money. My customers & there homes & families are more important to me than the bottom line. My company and my dealers that I sell to have replaced 100'S of ventfree [ROOMVENTED] products in the area's my personal stores are in we have replaced well over 400 ventfree LOGS & FIREPLACES with directvent products. We have added many more fireplaces in homes where they have removed there space heaters as well. They we all removed because of these reasons. The consumer would say. The heat is great. BUT I can't stand the smell. I have this white chalkey film all over my brick ,stone , tile on the front of my fireplace. [just think about what your breathing.] I get headakes all the time when my heater is on. It sooted up my house. There is so much water. I have to keep rags laying in my window seals. It seems my children are sick from the time we turn the fireplace on till the time we stop unsing it in the spring. I have been hearing these stories for over 20 years now. I have worked hard to inform the public in the areas we work. Ventfree products are not good for our families , homes, or our health. I have had other companies try to lable my company and my self as A liar , exstreamest, alarmest, & just a plain nuts . What amazing to me alot of these comments are made by those that I'm helping to sell 1000' up on 1000 of dollars of there gas. Why is that. Could it be like alot of other things in this country today. They don't want the public to know the truth. Do the research . Its just sad that you can't find out correct information by most who sell the ventfree ROOM VENT products. Make sure you always buy a vented product. I would choose a directvent with the sealed combustion chamber. Don't be mislead .Alot of directvents on the market can heat a home . The up front cost for a directvent may be a little more but it elimates all the issues that are caused by a roomvented ventfree product. The directvent can be used in any room . Can be used 24 hrs per day . Also they don't cost any more to operate than a ventfree product. Most people that sell ventfree try to may the consumer belive ventfree use much less gas. The orfice measures the fuel that comes into the fireplace ,log or space heater. If it a 30,000 btu orfice it 30,000 btu's. vented , unvented or directvent. That is all the gas per hr that will be used.. Gas is a great product it provides great heat. It just should always be vented.. THANKS, for trying to help inform the public about THE DANGERS OF VENTFREE PRODUCTS.

Sun, 10/11/2009 - 12:26

unvented heaters
by Paul Hempel

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Mr Wilson's article is spot on recommending avoiding vent free gas appliances, but there are some other negative issues he didn't touch on that can make them even less desirable.

The first is that all the gas industry research he mentions is done under ideal conditions, which of course don't exist in the average home. If the logs are even slightly mis-aligned, if there is any dust or pet dander on them, the chances of sooting and the production of toxic by-products will go up dramatically.

And secondly the vent free appliance uses room air for combustion. If that room air is contaminated in any way with say paint fumes, cleaning products, or off-gassing from new carpet or other building materials, all those contaminates are mixed, burned and sent into the room air as a potential witches brew of unknown compounds for the occupants to breathe.

We all understand that the one downside of tighter, more effecient housing is the potential for indoor air quality issues. To install a room vented appliance in a tightly sealed home is sheer folly, and should be actively discouraged by all industry professionals.
Paul Hempel

Sun, 10/11/2009 - 13:16

Impact of burning contaminants in the house air
by Alex Wilson

Helpful? -1

This is a great comment on the risk of using household air with contaminants as combustion air then venting that into the room. I had never thought of the issue of burning existing contaminants and, in the process, making them more hazardous. Another important reason to ban--or at least avoid--these combustion appliances! Thanks for the input. -Alex

Wed, 10/14/2009 - 08:17

Gas Fire logs
by Thomas

Helpful? 1

So what are the options / do I put glass windows on the fireplace and vent out the chiminey using the radiant heat source. How can I get the maximum efficiency for this situation.

Thu, 10/15/2009 - 09:20

unvented heaters
by Paul Hempel

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Fireplaces tend to specialize in maximum aesthetics, not maximum efficiency.

Burning with glass doors/windows shut will cut the energy coming into your room tremendously, while still drawing unacceptable amounts of room air out the chimney. They will tend to smoke up until you can barely see the fire. Neither you nor the fireplace will be happy.

If efficiency is your goal, consider installing a fireplace insert with a full liner. Inserts require just a fraction of the room air for combustion that an open fireplace would consume. Modern inserts also have large viewing windows that stay relatively clean. They allow you to both enjoy the fire view, and heat your home efficiently.

Your other option is to use the fireplace only during cool spells in the spring and fall when your furnace will not have to waste too much energy heating up replacement air lost to the fireplace. A tight sealing damper and glass doors will help save energy when the fireplace is not in use.

While many of us are open fireplace enthusiasts, open fireplaces are an archaic technology, and likely don't have a place in a tight, modern home striving for energy efficiency.

Paul Hempel

Thu, 10/15/2009 - 14:09

by Perry Bumpers

Helpful? -1

Thomas , If you want the most efficiency from your fireplace . Use a directvent gas insert. This way all your combustion air comes from out side of your home. Some directvent inserts are at 80% efficiency. Directvent product are the best choice for our families ,health & our homes.

Perry Bumpers

Sat, 10/17/2009 - 17:30

Unvented Gas Heaters
by Anonymous

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Can an Unvented Gas Heater be converted to a Vented one? How is this done.
Thanmks, Bob Franks

Sat, 10/17/2009 - 18:06

by Martin Holladay, GBA Advisor

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Tue, 10/20/2009 - 13:45

unvented gas heaters
by Dave Maupin

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For the past three years we have used an unvented gas log heater on the main level and an unvented gas wall-mounted heater in the basement. Both are 30,000 btu units. While there is no noticeable odor when we are inside the house, we have noticed a distinct odor upon entering the house. In addition, a film gradually appears on the windows when we use the heaters and, as we have a number of floor to ceiling windows this presents a problem. This year I have noticed a sensation in my lower throat and lungs, much like a sore throat others have commented on, that isn't there in the seasons when the heaters are being used. We're planning to look into units that are vented from the outside. Any suggestions?

Tue, 10/20/2009 - 14:13

It's hard to make a recommendation without inspecting your house
by Martin Holladay, GBA Advisor

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Clearly, it's time for you to stop using unvented heaters.

Most homes are heated by a vented furnace or a vented boiler. It's also possible to heat a house with hydronic radiators served by a water heater, a vented wood stove, or with an air-source heat pump (for example, a mini-split). There are lot of ways to heat the house, and your choice will depend on a variety of factors, including fuel availability and the configuration of your home. One thing's for sure: you have clearly explained why no one should try to heat a home with an unvented heater.

Mon, 12/07/2009 - 16:58

unvented heaters
by Mark

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We have unvented logs in the house we bought and we haven't had any trouble with them so far. Of course they are in the formal dining room and we are lucky if we use them once or twice a month, and then only for a max of a couple of hours. For the amount we use them I'm not sure it's worth switching to get a new gas insert. Our chimney is "decorative" only. We we have to have it lined in order to use a vented gas insert?

Tue, 12/08/2009 - 05:55

Decorative chimneys
by Martin Holladay, GBA Advisor

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A decorative chimney is not a chimney; it's more like a theatrical prop.

Of course, if you have a new fuel-burning heating appliance installed, it will need to be properly vented. Modern venting options include metal flues (stainless-steel or galvanized) or plastic vents (for condensing appliances). Building code requirements for flues and chimneys are strict. If you are unfamiliar with code requirements, don't guess at venting details. Hire an HVAC professional.

Sat, 02/27/2010 - 09:40

Open the flue
by George

Helpful? 1

We have ventless gas fireplace logs. We don't run them alot, but I'm wondering if there is a way to sort of mitigate the potential problems with ventless logs. For example, what are the consequences of running ventless logs with the flue slightly open? I understand that the flue would then need to be closed when the fireplace is not in use, or install glass doors that can be closed when it is off, but are there other issues? Besides the loss of some heat, do they not function properly ins some way, or cause more sooting, etc? Thanks.

Fri, 10/15/2010 - 08:12

Open the flue
by Mary Ann

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i am inteested in the answer you gave Georg e (FEB 27, 2010) about potential problens of opening the flue . For example, what are the consequences of running ventless logs with the flue slightly open. Thanks!

Fri, 10/15/2010 - 08:39

Response to George and Mary
by Martin Holladay, GBA Advisor

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George and Mary,
Your questions are confusing. Both of you asked about adjusting the "flue" on a ventless fireplace.

By definition, a ventless fireplace has no flue. It is ventless and flueless. Basically, your living room is the flue. The combustion byproducts stay in the room; there is no flue to carry these gases out of the house.

Sun, 10/17/2010 - 02:28

Unvented gas heaters
by Marc

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I grew up with unvented gas heaters here in south Louisiana. It was a very common means of heating older houses here. I cant stand the chlorine-like smell fron these heaters.They also make a room stuffy(probably from the nitrogen dioxide). I now have cardiovascular disease and don't want to be around these heaters because I can't stand them. Many years ago my great grandmother had asthma and heated and cooked with a coal stove because these gas heaters made her sick.They are very unsafe. Use an electric heater or a heat and cool window or wall air conditioner or a ductless mini-split air conditioner(one that has either electric strip heat or a reverse-cycle heat pump)instead if vented gas heat is not an option. In our cooling-oriented climate with mild winters(1000 heating load hours) this is a more cost effective option. Not many contractors here know too much about installing vented gas heaters here anymore. They have to be ordered.I understand that they have banned the installation of any new VENTED gas wall heaters because they are worried about having a fire start inbetween the studs because of the high surface temperatures. I've also seen more than one of these heaters improperly vented(having an upvent heater vented out through a side wall without going up to the roof. Not enough of an updraft up the flue.)

Sun, 10/17/2010 - 04:53

Response to Marc
by Martin Holladay, GBA Advisor

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You wrote, "I understand that they have banned the installation of any new VENTED gas wall heaters because they are worried about having a fire start in between the studs because of the high surface temperatures."

I've never heard of such a ban. The danger you allude to might arise from a faulty installation of a flue through a wood-framed wall. But most vented wall-mounted heaters I have seen are sealed-combustion units with a pipe-within-a-pipe configuration: the outer pipe brings fresh outdoor air to the burner, while the inner pipe is the flue. Such systems are very safe, because the outer pipe stays cool.

Wed, 10/20/2010 - 01:36

Let's push for a national ban on these heaters
by Marc

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How can we get the manufacture,sale and use of these heaters banned on a national level?
A good law would be If the gas was shut off for any reason the premises would have to be inspected.This would prohibit gas from being turned on if they have these heaters installed.
The meter would be locked by the gas company and couldn't be turned back on until they were removed and vented fuel-burning(or electric )heat was installed. We need to get tough with these heaters.

Wed, 10/20/2010 - 07:48

Banning unvented gas heaters
by Alex Wilson

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Martin (through Energy Design Update) and I (though Environmental Building News) have argued for years that unvented gas heaters should be banned. But during that time, regulations have been relaxed, not strengthened. In fact, free trade agreements, as I understand it, have made it really difficult for smart places--like Canada--to maintain those bans.

Sat, 11/06/2010 - 10:03

Thanks for your concern
by Anonymous

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Thank all of you for your comments, but given the choice between running my unvented gas heater and dying of hypothermia, I'll take my chances with the heater. Keep all your nanny state whining to yourself about outlawing these things.

Whatever happened to the freedom to accept a known risk? I have a small disability pension, and if all you do-gooders had your way I could freeze to death, but you'd get to feel good about being so enlightened.

I already live on a food budget of $3 a day. Running the furnace also spins the electric meter, you know. Maybe some of you geniuses have some good ideas about what else I can do without so you can protect me from myself?

Go pack sand! If these heaters aren't for you, by all means don't use them, but leave me alone!

Sat, 11/13/2010 - 21:00

Unvented might be necessary
by GO5

Helpful? 1

I use an unvented natural gas heater in an old house that's pretty drafty, so I'll assume that it counts as a kind of default venting. The water vapor doesn't seem to be an issue. I live on social security, so it was difficult to afford the cost of venting, and given my house, practically impossible to find an easy solution for a vent. I don't disagree with banning such appliances if they are indeed that dangerous, but the industry or the government will have to make the alternatives affordable to those on fixed income. Electric heating in my area is twice as expensive as gas, and oil is hopelessly expensive. Kerosene works OK, but really does smell. I don't have many choices except moving to a warmer state.

Sun, 12/05/2010 - 21:43

Unvented Gas Heaters
by Anonymous

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I have THREE unvented heaters in various areas of the house. It's a big house, and they aren't the primary heat source. Also, it's an old house and, in spite of doing all the tightening I can, it still doesn't compare in tightness to a modern house.
I've used these heater for years and I love them. They give FREE hunidity as a by-product. That is not possible with any other system. They have less of a carbon footprint per BTU than any other combustion heating system.
I agree that there is some soot with the system. I'm willing to clean the soot twice a year. If it's killing me, it's sure taking its time about it. I feel fine.
Here's a thought for the few of you above who feel compelled to regulate what heaters I can you use in my house: mind your own damn business!

Mon, 12/27/2010 - 13:18

To Martin Holladay, open flue question.
by todd

Helpful? 0

How is the question that george & marry asked, confusing???? Obviously they have the unvented logs ( in the fireplace ), That's why they are asking the question about opening the flue...Dahh.
opening the flue slightly is a good idea!!! Just make sure that your flue is cleaned out at regular intervals. Good question Marry & George.

Mon, 12/27/2010 - 13:45

Response to Todd
by Martin Holladay, GBA Advisor

Helpful? 0

Your speculation might be correct, but I'm not sure. You theorize that George and Mary have installed a ventless gas fireplace inside an otherwise unused brick fireplace with an operating flue controlled by a damper.

It's an odd arrangement, but it's certainly possible. Suffice it to say that this would be an inefficient way to burn natural gas. Opening the damper on your chimney will result in significant heat loss.

Sun, 01/16/2011 - 22:44

open combustion vented heaters banned
by Marc

Helpful? 0

I wish to correct my earlier post. I found out that open combustion vented gas wall heaters are banned under the newer editions of the International Fuel Gas Code.The reason is that the products of combustion can mix with the room air at the draft diverter at the top and also spill out of the bottom of these heaters (even with no backdrafting) and create a carbon monoxide poisoning potential.

Thu, 05/19/2011 - 12:53

Cities Certain Municipalities Ban Vent-Free More Than You Think.
by Gas Man

Helpful? 0

While I am mostly, in full agreement with your article and as an HVAC professional I have been writing about this issue since about 1996, just before the American Gas Association Research Division released their test report which became the basis for more approvals in the USA.

My article from 2009 outlines many cities, towns and regions throughout the U.S. who either continue to ban them or strictly control their installation. Incidentally, the two provinces in Canada that did originally accept them have long since repealed their approvals. All of Canada is once again banning these products. Please see my list at,

Keep up the great work Alex, the more voices we can have speaking out against the propaganda being spread about by the Vent Free Gas Product Alliance they better chances we have to inform potential consumers against their use.

The Gasman

Thu, 05/19/2011 - 13:22

One Small Correction On Combustion Efficiency and By-Products.
by Gas Man

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You wrote: <"To dig a little deeper, let’s take a look at combustion. When we burn a hydrocarbon fuel, such as natural gas or propane, the fuel reacts with oxygen producing heat and two primary combustion products: water vapor and carbon dioxide."> Something most people overlook is that the water vapor from natural gas and propane combustion has an average acidity rating of about PH 4, which is something like the acidity of a can of Coke. SO2 is another byproduct of combustion.

You also said, <"The first is that, along with water vapor and carbon dioxide, there are some combustion by-products that aren’t good for us. With an unvented gas space heater, the combustion process is very complete--99.9% efficiency or higher, according to manufacturers--but that tenth or hundredth of a percent can be pretty nasty, containing constituents as carbon monoxide, nitrogen dioxide, soot, and unburned hydrocarbons."> Many people have made the mistaken assumption that 99.9% combustion efficiency means their is nothing else to worry about. However, while most of these products do combust 99.9% of the fuel injected that simply means that approximately .1% of the methane is unburnt. Products of combustion include up to 12% CO2, anywhere from 100 to 1000 ppm of CO (carbon monoxide (for the first 5 to 15 minutes of operation) as tested by accredited test agencies, water vapor as you have discussed and NO2, SO2. So please don't confuse the combustion efficiency with emissions. Combustion efficiency is the same with vented or unvented gas appliances, it's just better to know that all of that nasty stuff is being venting to the outside rather than into the lungs of children.

You may want to read my article from 2009 on the AGAR report and product sizing...

Also, I discussed combustion efficiency in an article I wrote in 2007 here:

Lastly, I offer a number of comments on the safety and accuracy of the ODS pilot systems used by these products in my article from 2002.

The Gasman

Sun, 10/23/2011 - 18:23

Unvented Gas Heaters
by Jim Brook

Helpful? 0

I assume all of you in favor of banning unvented gas heaters are also in favor of banning gas ranges and cooktops.

Mon, 10/24/2011 - 05:33

Response to Jim Brooks
by Martin Holladay, GBA Advisor

Helpful? 0

Building codes in most areas of the country require the installation of a vented range hood above any gas cooktop. Assuming that the homeowner uses the range hood, that means that the products of combustion are being vented.

Thu, 02/02/2012 - 21:00

by Kirk Bowman

Helpful? 0

Got to love all of the assumptions and scare tactics that go into these articles. With a complete burn you are left with water vapor and CO2. Only 0.1% is not burned completely. That means a 30,000 BTU vent free system burning nonstop for 31 straight days will produce a total of 21.67 cubic feet of unburned gas. That's enough to fill almost a whopping 3% of a 10x10x8 foot room! Guess what? That's the MAXIMUM amount at 99.9% efficiency. Since no room, let alone an entire house, is completely air tight can you guess what that means? That means a portion of that will escape outside. Open a door? Gasses go away. Turn on your bathroom fan? Gasses go away.

People like you are a strain on the world. Human beings, with normal, clean air emit carbon monoxide, methanol, ethanol, ammonia, acetone and a host of other products that you all are freaking out over every time they exhale. That's right, those are byproducts of normal breathing. You get more carbon monoxide by having a group of people in your house just breathing than you do from a vent free system.

This next quote by Gas Man is the funniest part of all of the comments, "Combustion efficiency is the same with vented or unvented gas appliances". That's just straight up BS. The combustion efficiency for vented furnaces isn't even the same between models, let alone compared to vent free systems. That's why vent free systems make more BTU's per the amount of gas used.

Now, should vent free systems be the only source for heat? No, because the vent allows for better air quality because vent free systems DO make a big change in the amount of CO2 in the air. No heating source period should be used without ventilation of some kind to prevent stagnation.

Dave Maupin wrote "This year I have noticed a sensation in my lower throat and lungs, much like a sore throat others have commented on, that isn't there in the seasons when the heaters are being used." Congratulation sir, you got sick one time in 3 years during flu season. That's actually better than most people with vented or vent free systems.

Thu, 02/02/2012 - 22:07

Response to Kirk Bowman
by Alex Wilson

Helpful? 0

For sake of argument, let's suppose you're right and the tiny amount of unburned hydrocarbons and unintended combustion products like carbon monoxide introduced by an unvented gas heater are fine to live with. There is still the issue of the water vapor, one of the two primary combustion products from hydrocarbon combustion. A 30,000 Btu/hour unvented gas heater will produce about a third of gallon of water into the home per hour. If used for long periods of time, that's a lot of water. Most building science experts don't want that level of water vapor introduced into highly energy-efficient homes--which most of us on this forum are focused on. It just doesn't make sense, particularly during the spring when humidity levels in homes are often already rising and it may be tempting to turn off the main furnace and rely just on the gas space heater.

Fri, 02/01/2013 - 19:36

Edited Fri, 02/01/2013 - 19:38.

Perry Bumpers comment on efficiency
by dave varez

Helpful? 0

I'm not arguing for unvented heaters , I'm not qualified to decide one way or the other , but it is hard to accept the scientific dogma when one claims that

" Most people that sell ventfree try to may the consumer belive ventfree use much less gas. The orfice measures the fuel that comes into the fireplace ,log or space heater. If it a 30,000 btu orfice it 30,000 btu's. vented , unvented or directvent. That is all the gas per hr that will be used..

Uhhhh.... yeahhha , "all the gas that will be used in an hour" - but the unvented heater is more E-F-F-I-C-I-E-N-T , so it will produce the same amount of heat in LESS HOURS .
I have an unvented heater , but tend to not want to use it other than in emergency situations .

But how am I supposed to be convinced of the science by comments that contain statements that make no sense?

Sat, 02/02/2013 - 05:49

Edited Sat, 02/02/2013 - 05:51.

Response to Dave Varez
by Martin Holladay, GBA Advisor

Helpful? 0

Dave Varez,
You're right, of course. However, there are plenty of people making cogent arguments against the use of unvented gas space heaters. To make a decision on this issue, we don't have to listen to people who make unscientific comments. You are free to ignore anyone who isn't making sense.

Here are the facts:

1. Unvented space heaters are more efficient than vented space heaters, because none of the heat output goes up the flue. All of the heat output (as well as the combustion gases) stay in your living room.

2. The gains in efficiency are not worth the risks to your health.

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