Any one of several gases is used for cooling (back filling) vacuum furnaces;
There are many places to find gas furnace prices. One can look on sites like Furnace Price Guides, Century Gas Furnace, and Consumer Reports. One can also find gas furnace prices by going to a local heating supply store.
One could find information on gas furnace troubleshooting online at Ask. Hvac for beginners is also a great place to look. One could also contact their local gas furnace dealer and/or repairer for gas furnace troubleshooting.
On the inside of one of the removable panels
There are many places online where one could purchase a gas furnace. One could buy from Lennox, Holmes Heating, Express HVAC, Bryant, Ruud, or even eBay.
sometimes getting a gas furnace can vary and you can get them from a lot of places just like craigslist and from amazon and from walmart the dot com one
Of course If the flue is sized properly
Could be a drain for the inducer motor if it has one and it depends do you have a a/c coil on your furnace if so it could be a drain for it.
The thermocouple tells the gas valve to supply gas to the burners. If the thermocouple is bad then the furnace will not work or the pilot will not stay lit. A properly working one will have a reading of at least 12 milliamps.
Read the tag on your furnace for the input/output rating. American Standard and all other manufacturers make more than one size furnace.
it depends on how well maintaned it is should be inspected every year ,please do not go to one hour furnace they will tell you you need a knew one when you don't
Need to know what type of furnace, electric, gas, or oil before question can be answered.
There are a variety of gas furnaces that can without much effort be converted from one type of gas to the other, Natural gas and propane gasses work at different pressures; one gas is denser than the other.Converting gas to an electric furnace, you would be gutting almost the entire furnace, and replacing the gas components with electric heating coils, diodes and relays. This will take a lot of man-hours, fabrication, engineering, and parts. while not imposable, the conversion would be very expensive.