When Robert Coffman began checking homes for energy efficiency, he discovered some had far more to worry about than drafty windows.

In the past few years, Coffman, owner of Airtight Energy Audits, has visited between 25 to 30 homes that have had high levels of carbon monoxide, a colorless and odorless gas produced by incomplete burning of fuels.

And, he has seen at least 10 homes in Lawrence where the levels of the gas could have been fatal.

“I was completely caught off guard. I didn’t realize there would be that many people with numbers like 1,600 to 2,000 part millions, which can be deadly very quickly,” Coffman said.

As the days turn colder and furnaces are turned up higher, making sure that fuel-burning appliances aren’t spewing carbon monoxide is important, said Curt Floerchinger, with Black Hills Energy.

“If you got a carbon monoxide problem to start with at a lower levels, there is always a real potential for it to increase to a dangerous level,” Floerchinger said.

Each year, carbon monoxide poisoning kills more than 500 people and sends another 15,000 to the hospital. Because the gas can’t be seen, tasted or smelled, it is nearly undetectable.

Physical signs of carbon monoxide are flu-like symptoms such as headaches, nausea, dizziness, light-headedness or shortness of breath. Another sign of carbon monoxide is moisture or frost on the inside of windows.

Floerchinger recommends homeowners install carbon monoxide detectors. The detectors should be put on the lowest level of the home because the gas sinks. Also, they should be near sleeping areas.

Just like smoke detectors, carbon monoxide detectors need to be regularly maintained with batteries replaced annually and the alarm tested monthly. Some models are combined with smoke detectors. Floerchinger recommends purchasing higher-end detectors, which he said have a longer life.

Carbon monoxide can escape into the home when a furnace’s heat exchanger cracks or when the flu pipe isn’t properly vented to the outside. Floerchinger recommends having the furnace checked each year, which will help catch maintenance problems before they become expensive to fix and test for carbon monoxide.

In the case of the homes Coffman found with high levels of carbon monoxide, the fact that the home was so drafty was a saving grace. But, since the goal was to close those air leaks, Coffman said the amount of carbon monoxide being pushed into the air would have been much more dangerous once energy efficiency measures were taken.

Coffman wasn’t the only one who found homes with high carbon monoxide levels. Another local energy auditor, Kirk Devine said he came across quite a few homes in Kansas City’s older and lower-income neighborhoods that had high levels.

“It got so we did the testing at the end of the audit so we could complete it,” Devine said. “It was a regular occurrence and happened pretty frequently, and there were some bad ones”

Finding homes with high levels of carbon monoxide in Lawrence was rare, he said.