Does gas furnace need exterior air or interior air

the furnace should have never been installed without combustion air in the first place, is it in the attic, basement, closet? The amount of combustion air depends on the btu's. you can run ,metal ducting to the space. propane is a heavy gas and needs to be installed carefully so gas cannot puddle and fill up a specific application if not installed properly.

Make sure the kit included smaller sized orifice's and spring kit for the gas valve. The number on each orifice should be cross referenced with total btu's rating of the furnace. It does seem like there is too much fuel or not enough air intake (combustion air). The inches of W.C. seem fine, but you still may be getting too much volume of fuel with too large of sized orifice's. Hope that helps

First, check the drainline from the furnace. You have a 90% gas fired furnace. Where 80% furnace has 1 heat exchanger, yours has 2 heat exchangers. And the second heat exchanger will cool the exhaust enough, that it ends up below the dew point, and your furnace outlet/exhaust will condensate. This drain is probably stopped up. Now, I've installed and service many of these systems and I've only seen the piping at the roof you described once. And that was when the roofers replaced the roof, damaged the furnace flue pipe, and tried to repair it themselves. Normally, and this may not apply to yours, we tie in the exhaust/supply lines about 2-3 ft. above the furnace. Then 1 pipe goes through the roof. Thus 1 pipe is a kit that has an inner liner & outer pipe(2 pipes in 1). Now I'm not sure if this is a problem or normal for your system, but it may be worth looking into. You should be able to find it in the installation manual, or call a local parts house that sells your brand, or as your tech. And if it's just your drain, forget all about the piping I mentioned. Hope this helps!

you need to purge the line of air do this outside first , you will also need to do this at the furnace crack the joint at the gas valve /service valve ,but propane is heaver than air so be very carefull doing this , or call in a gas fitter to do this job

well lets start with the 2" pvc pipe. that is a combustion air intake it does not put air into the room, i hope. this is a 90% furnace and they should have installed it that way. there should be 2 pipes to the outside the other is combustion gases. the dust problem maybe caused by the air return pulling the air to that room. the bedroom normaly does not get the trafic that the rest of the condo does.so it would not have as much dust.

Yes it can do but you will be better off by gone to a gas heater. MY own furnace was chance over to propane and didn't workout to good. Less then ayear i have put in a new heater. Ken's Repair

Well if it not in the boot looking thing coming off the side of the furnace then it is most likely inside the furnace.

where are you getting combustion air from now in the midwest 1sq" per 1000 btu York.com with the model number

If your furnace is easily accessed in the basement or a closet etc. then likely the filters are located either in the bloer compaertment (the small panel on the furnace) or in the ductwork attached to the furnace. There should be a removable cover. The size varies dedending on the size of your system. When you remove the old one it should be printed on it or you can measure it.
If your furnace is in the attic or a crawl space then you probably have filter grill(s) in your return air. Usually centrally located in the home.
Filters should be changed as needed depending on how you use your system but usually every 30-90 days.

sounds like you need a gas valve or inlet pressure adjustment. You will need a proper pressure guage for this.