Propane is a very clean burning gas that is cheaper than heating with electricity and can be used for heating where there is no electricity.
But it does have a bit of a downside in that it creates Carbon Monoxide as a byproduct when it does not fully combust or is used at a large volume.
Carbon Monoxide, when it is breathed, can make you sick and even lead to death. That is why it is called carbon monoxide poisoning.
That is also why even though propane is a clean burning gas, it also requires that you take the proper precautions while using a propane heater to warm your area.
Outdoor propane heaters do not require extra ventilation because they are as you say “in their natural habitat”.
Any carbon monoxide created while using one dissipates naturally in the wind.
On the other hand
Propane heaters that are rated for indoor use have a number of safety precautions built in to help protect you.
An oxygen depletion sensor (ODS) shuts the heater down when it senses that there is not enough oxygen in the room.
The reason there would not be enough oxygen in the room is that it is being displaced by carbon monoxide.
But even though that is an awesome feature, it does not however detect carbon monoxide or detect propane.
That is why that while using a propane heater indoors, even if it is rated for indoor use,
It is suggested that you provide extra ventilation and that you install a carbon monoxide detector as well as a propane and natural gas detector.
Propane in its natural form is completely odorless. For that reason, it has a chemical called Mercaptan added to it. The result is a smell that is similar to rotten eggs.
If you have a propane leak, the first indication is the rotten smell coming from the heater or Propane tank.
That’s the signal to turn the heater off and get it fixed.
But depending on the smell itself is not full proof. There are many things that can blind your sense of smell
What about the garage?
The garage is a grey area when it comes to heating with propane.
If the garage is small enough then an indoor propane heater like a Little Buddy will give you plenty of heat.
But if you have a large garage, then you’ll probably want an industrial size heater.
But either way, you will need ventilation.
Do you need ventilation when using a propane heater?
Propane heaters are specifically rated for indoor or outdoor use.
When you are using an outdoor propane heater outside where it belongs, the wind provides all the ventilation you need.
Indoor propane heaters come with extra precautions as a necessity because of the lack of ventilation inside of a house or building.
An oxygen depletion sensor is installed on indoor propane heaters to shut the heater down in case the oxygen in the room becomes too low.
If the oxygen becomes too low, then the result is carbon monoxide. Which can lead to poisoning or even death.
Providing the extra ventilation will ensure that your oxygen depletion sensor never has to shut down your heater and that your room does not fill up with carbon monoxide.