Surprisingly, gas ovens are allowed to produce twice as much carbon monoxide as a gas fired heating system even though a furnace/boiler is vented to the outside.

The standard (800 ppm's air free) was approved in 1927 and we are still using it today.  This is despite the fact that modern homes are substantially tighter than in the 1920's.

Again, we recommend that if you use an HVAC company that has combustion test equipment, have them check the exhaust from the oven while they are in your home.  Often, adjustments can be made to the oven burner which lowers carbon monoxide production.