If you keep the wick on the kerosene heater clean, frequency depends upon the hours that it is used and how clean the kerosene is, your fumes will be cut drastically. I cleaned my wick at the end of each winter. Replaced it every other year and with my orchid flowers being very sensitive to ethylene pollution, I never had a single blossom damaged. Not one.
I think ethylene comes from usage of kerosene and other hydrocarbons, from the uneven burning. Kind of like a by-product.
When kerosene heaters first came out in the early 80's, maybe a little earlier, so many problems occurred because people ran out of, or would not use, kerosene. They substituted gasoline!!! Big no-no. That lead to many explosions, fires and deaths. Kerosene was more expensive.
"Oh, kerosene heaters were bad, they were dangerous"!!! The heater didn't put gasoline in it instead of kerosene, a stupid human did! I used one for 28 winters. 28!!! I would not hesitate going that route again.
Plus the room/greenhouse must be properly ventilated! It can't be sealed tight. I use to crack a window in the greenhouse and cracked open the sliding glass door to my dining room.
