Im framing my basement, and need to box in my furnace and gas boiler...how far must the wall be in front of gas furnace? Can I simply use drywall in front of the furnace, or should there be a grate or louvered door with slats of some kind?

 

Code in your area may be different, so please check locally. But I think the following is probably true.

You need 36 inches of working space in front of your furnace (with the door closed). The furnace specifications will tell you the required clearances on the sides and back, but it's normally not too much.

You may be required to use firestop drywall on the inside of your furnace room wall, but in my area you don't need to put anything on the inside of the wall (i.e., open studs are fine). Of course, there would be drywall on the outside of the studs.

You need some ventilation for your furnace for combustion air. In new homes, this is usually done by two ducts bringing outside air into the room (one near the ceiling and one near the floor). Alternatively, most areas will allow you to use louvered doors instead. The key of course is to provide sufficient combustion air so that your furnace isn't tempted to pull exhaust gasses down the flue and kill you.

The amount of ventilation varies depending on the size of your furnace and your water heater(s). Add up the input BTU of all your gas appliances. You need about about 1 square inch of vent opening for every 1000 BTUs. Example, a 10x12 vent would serve 120,000 BTUs. But please check local regulations -- they may be different. Your furnace manual may give ventilation requirements too. I think the requirements are different depending on whether you're supplying outside air, or air from the rest of the basement.