This time of year I always worry about my non vented propane heater causing problems.(I use a combination of electric and gas for heat in the winter)

In the past with only citrus I have noticed almost no issues with using unvented heater.

This year I have added new tropicals including 5 Bananas a few Pineapples and papaya.

My question is dose anyone with experience know if this is going to be a problem with these new additions.

I watched a video on e-University, where the University still recommends not using non vented heaters. They still put some ethylene gas into the greenhouse. - Millet

What exactly are (un)vented heaters? Is the difference that one uses air from within the room it is located and the other one takes outside air?

A non vented uses only the air inside the greenhouse. So the exhaust gases are vented inside.

A vented heater is set up to vent the exhaust gases to the outside. So there are heat exchange coils to keep most of the heat of combustion inside while exhausting all combustion products outside.

The combustion products aren't all just water and CO2. Millet is saying there are traces of things like ethylene and other things that could harm your plants. How many things like ethylene depends on the fuel source and it's purity.

If nothing else non vented causes a lot of water vapor to be released into the greenhouse.

With non vented some recommend allowing air exchange in/out of the greenhouse. If you do that you are losing heat just like the vented loses some heat.

Fruit nut on you first sentence I think you meant to say "not vented to the outside".

Non vented heaters have to be kept in good condition at all times, so that the combustion burns pure. As they get older, or become dirty over time from use, they put out more ethylene into the greenhouse. Further different type of plants are more or less sensitive to being damaged by ethylene gas. Personally I would not use them, but I have seen them in greenhouses. - Millet 3042

I am not really on topic with this but what about the usage of petroleum heaters? I can't imagine that they are all that good inside a greenhouse as well.

Ryan, I do not know the answer to your question. You might find it on the internet. Some years ago, I had infrared propane heaters put into my greenhouse as back up insurance heaters ( got them for free, and installed for free). I remember when I had to use them for a couple winter nights, I noticed a fair amount of leaves quickly turn yellow and fall from the plants, do to ethylene gas toxicity. Other than the damage to a pomegranate tree, I really don't remember what all I was growing at the time, nor do I know what the PPM level of ethylene the infrared heaters put out. - Millet