If you research this you will find the answer to be a resounding NO…!!! THEY COULD BE WRONG and here is why. If it is dangerous and if you will get carbon monoxide (the most often cited danger) then you better forget cooking the turkey for thanksgiving. Why is turning on your oven for 3-5 hours to cook a turkey okay and turning on your empty oven for an hour or two to warm up your kitchen (and dining and living room in today’s open design homes) not okay?
First of all, many vent less gas log sets found all over the world and very common here in San Miguel de Allende burn less efficient on purpose. Some have a yellow flame like a real fire which may indicate lower temperatures and incomplete combustion. Your oven should have a blue flame which means it is more efficient than many of the alternative space heaters using propane or natural gas including vent less gas log sets. Ovens are built to bake bread, cook a turkey and keep food warm for hours and hours at a time. They are usually not vented, poorly insulated and let all of the heat into the room which makes for a decent source of heat. If there is carbon monoxide it should be well within standard limits, otherwise they could not sell you the oven for cooking.
The only real danger is if the oven flame somehow goes out while the valve/knob is left on and at the same time the safety malfunctions and sends unburned gas into the house. Does this happen when you are cooking a turkey? Note: newer gas log sets have an oxygen sensor that turns off the gas if the room becomes depleted of oxygen below a certain safe level. Does your gas heater have this safety feature? Your oven does not have this feature so be careful using you oven as a space heater.
Yes it is true, an oven was not made for space heating. But the blue flame of my oven tells me it is burning more efficiently than my gas fireplace log set. After an hour or so my eyes are burning from the fireplace log set. This is not the case with the oven. Distribution is a problem equal to both heaters. So I don’t recommend using an oven to heat a large area. But if your oven is safe to cook a turkey for a few hours, then it is safe to turn on with or without a turkey to take the cold edge off the kitchen in the early morning (never leave an unvented gas heater on while you sleep). Am I missing something here?