Buildings

Dangers of Vent-Free Gas Heaters

Q: Our house is often drafty and chilly in the winter, and since we're expecting our first baby next month, I've been thinking about ways to supplement the heat, at least in the baby's room. Our neighbor recently got one of those new 99% efficient vent-free gas heaters, and says it helps a lot. My sister says they're not safe and we'd have to be nuts to install one of those. I figure they have to be safe or the government wouldn't let them be sold. What do you think?

A: I think that our ancestors made a giant leap forward when they left the caves and moved into houses or tipis with chimneys to let the smoke and toxic fumes out of the house. And I can't figure out why so many people want to take a giant leap backwards and turn their homes into chimneys.

I've read the ads. I've looked at the units. I've read some of the technical literature. I've gone into homes with my carbon monoxide detector. The good news is that only a few of the homes with these units have high levels of CO. The bad news is that lots of them have low levels of CO, and there is an increasing body of medical evidence that low level CO exposure can have serious health consequences. So my opinion is that your sister is absolutely right, and if you care about your neighbors you'll convince them to get rid of the thing.

The process of burning produces byproducts, depending upon the fuel used, the availability of oxygen, and the type of burner. Burning gas typically produces carbon dioxide and water. It can also produce other gasses that can be harmful — nitrogen dioxide and carbon monoxide, for example.

If we accept — for the moment — the claim that these heaters are perfectly clean-burning (and, presumably, will stay that way for their entire lifetime) we'll still get the carbon dioxide and water. The engineers tell me that we'll get about a gallon of water in the house for every 100,000 BTU's worth of gas we burn.

Burn the typical unit for a few hours, and we're pumping more moisture into the air than we do when we take a shower. Most of us have learned that we need to run an exhaust fan in the bathroom when we shower, or we start growing mold in the house. We can, I guess, avoid the problem by installing an exhaust fan in the room with the heater to get rid of the water and prevent mold. But what does that do to our "99% efficiency"?

If the water hits a cold surface, it will condense and release that heat, along with creating a perfect vacation resort for mold. In addition, every owner's manual for a vent-free heater or fireplace I've looked at recommends you open a window when you use it. Now what happens to the efficiency?

Since they recommend opening a window, calling these things "vent free" is a bit misleading. The reality is that you have to supply your own vent — the window. Like any chimney, that window will let heat out of the house and may let combustion products out too. There's a nice romantic image: cuddle up with your wife in front of a nice dancing fire on the couch, which is in the chimney.

How "efficient" these heaters are is really beside the point. My colleagues and I and people we've talked with across the country have all been in homes with these supposedly safe heaters where we measured high levels of carbon monoxide. Perhaps even more significant is the fact that we've measured low levels of CO in dozens of houses.

There is a growing body of scientific research connecting low levels of CO with brain damage in adults, sudden infant death syndrome (SIDS) in infants, fetal abnormalities, and a host of lesser symptoms such as headaches, dizziness, nausea, and flu-like symptoms.