Re: Opinions: crawl space furnace location?
As an HVAC service tech/installer I HATE most crawlspace installations!
Yours sounds about the best scenario for a crawl though. I'm assuming crawl access is from inside the house? As long as there is clearance from support beams/posts to access the filter and be able to remove and replace any major components you should be OK.
As far as noise goes, most modern furnaces (mid efficient-80%+) are much quieter than the ones with the old belt-driven blowers. High efficient (90%+) furnaces with sealed combustion chambers are quieter still.
Having the unit sit on bricks on the floor, or suspended from the floor joists with vibration absorbing hangers will keep any vibration from traveling through the house. Also use canvas flex connectors between the supply and return ducting and the furnace to keep vibrations from traveling through the ductwork.
As far as air noise goes, that is a matter of having properly sized and designed ductwork and the choice of grilles/registers used.
If you are concerned about gas leaks, there are several LPG gas detectors you can use. Make sure it is mounted at floor level in the crawl, and that the alarm can be heard from the living space or it won't be much good!
Hope this info isn't too late! Just remember, that filter needs to be checked about once a month while in use. Dirty filters kill furnaces!