Toxic smell from Duraflame crackling log!?

This smell is lighter fluid that is embedded in the log. As you have found out and because you are an asthmatic, you are more sensative to their smells than other people. You might want to check your flue and damper because these logs do not usually emit lots of smoke which means that your draw was not working properly on your fireplace. Maybe a bird nest higher up in the flue? Something to consider but now, consider spraying Febreeze (if you can tolerate this due to your asthma). It may help kill the smell. Also consider getting some sort of charcoal base air freshner and put one in each room. Charcoal pulls smells out of rooms. I would close your house back up and let your furnace run. Then, go buy a new furnace filter and put it in later today. Good luck.