GreenHomes America

If you read no further, know this:  unvented fireplaces are a bad idea.

We’ve had a few responses regarding Carbon Monoxide lately, and for good reasons: it’s a concern we should pay close attention to.  As we button up our homes and keep warm for the holidays, some of us look to inexpensive solutions and quick fixes such as unvented gas fireplaces.

My personal experience so far suggests burning a fire inside just doesn’t seem like a good idea (don’t ask, just trust me on this one).

Up north in igloos, the Inuit used small oil lamps called Kudliks and vented them with smoke holes in those igloos.  Further south in a region many of us call home now, the Lakota used Tipis, and also showing great intelligence, had a smoke hole at the top.   Overseas, centuries ago, Romans built tubes in walls to draw smoke out of bakeries and what we now know of as a chimney may have started in northern Europe in the 12th century. So what happened?  Are we smarter now than all of our ancestors or have we failed to learn something, and as they say History is repeating itself?

Some manufacturers of vent-free appliances claim they burn so cleanly that they don’t need to be vented.  I have a hard time believing this since there will always be combustion by-products namely Carbon Monoxide and water.  I’ll discuss the CO side in a minute—CO kills.  But water is an issue for every one of these units, burning correctly or incorrectly.

Vent-free appliances can produce about a gallon of water in the house for every 100,000 BTU’s.  Leave one on for 4 hours, and you’re well beyond the moisture you’ll put in the air from a couple of showers and cooking a pot of spaghetti.  That’s why you’ll often see condensation on your windows or sense a clammy feeling in the air.  This humidity, if left unchecked can lead to other issues such as mold or rot.  Sure you can address the moisture by providing whole-house ventilation something we regularly recommend, but you will be paying a penalty over ventilating your home because you didn’t want to ventilate your fireplace.  You shouldn’t use your house as a chimney—that’s what flues are for!

Water is a serious problem—but it’s not the worst of it. Without regular service the stove produces more CO, and my science books suggest incomplete combustion creates more by-products.

The effects of CO can be overt or subtle but either way long lasting.   We pay attention to dangerous high level exposure, but even low level exposure over time can be debilitating.  From the American Lung Association:

Breathing CO at low levels regularly may cause permanent mental or physical problems. At very high levels, it causes loss of consciousness and death.¹

Approximately 450 people die each year from CO exposure related to fuel-burning, residential appliances. Thousands more became ill or sought medical attention.² CO poisoning is estimated to cause more than 50,000 emergency room visits in the United States each year.¹

The EPA suggests never heating your home with a gas oven.  Short term exposure might be ok but long term exposure is not, like when you are heating your home all day long.   For those without kitchen range hoods, or those who fail to turn them on, a stove is essentially an unvented gas heater, so why do we use unvented fireplaces?

Apparently there are safety features.  Some manufacturers’ fine print indicates you should open a window every time you use the appliance!  Who does that?  And if you’re supposed to open a window, it can’t be an unvented appliance.  I’m guessing the lawyers have paid attention to the potential liability from combustion gases and perhaps related moisture problems.  Other fine print from a vent free manufacturers retail site suggests that the Oxygen Depletion Safety Pilot device shuts off the gas before dangerous levels of CO can be formed, but says nothing about using a CO detector as a back-up. It also does not address long term low level exposure.

Since you can’t see or smell carbon monoxide, but high levels can kill you in minutes, it makes sense to have a CO detector.

Here is what an average off the shelf CO meter will do:

In accordance with UL 2034, the CO sensor will not alarm to levels of CO below 30 ppm and will alarm in the following time range when exposed to the corresponding levels of CO. 70 ppm CO concentration 60 – 240 minutes 150 ppm CO concentration 10 – 50 minutes 400 ppm CO concentration 4 – 15 minutes.

It won’t sound below 30ppm.

This link has a long list of letters from folks that have been harmed from high and low levels of exposure. Some when finding CO levels in their home, complained to the fireplace manufacturers who suggested the meters they had bought were too sensitive!  The last thing I want is a device that does its job too well.

It is wrong that our national code allows unvented gas fireplaces when we know they can be harmful. They should never be installed.  The consumer advocacy group, Consumer Reports justifiably suggests caution with these appliances and they also say that there is “No national standard that compels contractors to consider air quality when they install an unvented fireplace; the National Fuel Gas Code and many local codes call only for the fireplace to be sized so that sufficient air is available for combustion.” But this is not entirely true, as accredited contractors with the Building Performance Institute we can’t perform improvements on a home until an existing unvented heater is removed.  Why?  It’s not considered safe and the risks aren’t worth it.

Unvented gas fireplaces are a potentially deadly example of penny wise and pound foolish.  Let’s pay respect to those who figured this out a long time ago and keep ourselves and our families safe through the heating season.  If you have one, get rid of it.  If you’re thinking of adding an unvented appliance, please don’t.

Thanks and stay safe,

Jason.

 photo used under creative commons liscense from

1. Weaver LK. Carbon Monoxide Poisoning. 2009. New England Journal of Medicine 360: 1217-1225.Centers for Disease Control and Prevention. Nonfatal, Unintentional, Non-Fire-Related Carbon Monoxide Exposures—United States, 2004-2006.

2. Morbidity and Mortality Weekly Review 57:33 (August 2, 2008). Accessed October 20, 2009