The next day, Jim and his Dad came over early to look and see if they could figure out what exactly was causing the CO to leak out into the house. Mike, Jim's dad, said that we should go ahead and replace the entire stove/oven unit. When I woke up around eight, I text messaged my Dad to let him know what was going on. He came over, and said that it definitely was the oven and that we probably just needed a vent-a-hood to provide ventilation for the CO out of the house.
Then we called my Mom to let her know what was going on. She was out of town at a conference. She called a nurse that she works with whose husband is a plumber. He came out (with his really cute little girl!) to test everything. He ruled out that it definitely wasn't the heater and confirmed that it was the gas oven. The measurement was 13 parts per million of CO in the air when the oven was on; anything about 9 ppm is considered dangerous. He confessed that he wasn't an appliance guy, but that we could try the ventilation, but if that didn't work, then he would definitely replace the entire unit.
So, my Dad, Jim, and I went to Home Depot. We bought, or actually my Dad bought for us, an exhaust fan with necessary parts, strainer for the kitchen sink (to catch food since we don't have a garbage disposal), a rubber stop for the bathtub (so we can take baths), a new floor strip for the doorway between the dining room and laundry room, an extender for the shower head, and a CO detector that displayed the ppm in the air so that we could monitor things more closely and make sure the ventilation fan is working. THEN, he came over and installed EVERYTHING. We are very thankful that he is such a handy guy, and that he paid for and did all of the necessary labor! I love my Daddy!