It sounds like the heater is getting the air in the room so warm that it's making your eyes and nose hurt. That can be from dryness, from heat, or from combustion products.
Depending on the partucular model, you can try to:
- Turn the set temperature down.
- Turn the turbo fan to a lower setting.
- Turn the feed valve from your propane tank to a slower feed. At some point, you should be able to throttle the amount of fuel burning in a period of time to where the heat is more bearable.
- If you're smelling fuel, or overt burning petroleum smells, turn the unit off. This is a sign that things aren't burning right.
Last, but probably most important. If you are running a unit like this inside, make sure you have windows open. Please take me seriously here - installed propane furnaces have heat exchangers to pull in fresh air, heat it, and pass that air into your house. A propane heater burning inside your house is burning your inside oxygen and, depending on the flame quality, dumping Carbon Dioxide or, worse, Carbon Monoxide, into your house. You can end up dead pretty quickly, especially from Carbon Monoxide poisoning, and you'll likely be feeling fine right up to the time you pass out. These types of heaters are meant more for outside use, so please, if you absolutely feel you must run it inside, keep windows open and have a fan running. You're playing with your health