[FONT=Comic Sans MS]undefined[/FONT]I have a chance to get a newer Trane furnace for the cost off taking it out. They are rebuilding. The problem is it is natural gas now can I change it over to LP. and if so is it just the gas valve or also the orfices for the burners. It is Large enough to heat my 43x70 shed and comes with central air also. Thanks for your time. John

Background: 11 month old house; Bryant high efficiency gas furnace; Honeywell programmable thermostat. I keep the house fan on for even temperatures between floors. During construction, an independant company came and inspected for energy efficiency (insullation, house leaks, etc.) Problem: On cold day (-3F), furnace reached only 63F when demand was 68F I checked & replaced filter and thought I was OK - the furnace worked all day and finally got to 68F.. 5 days later, it got cold again (-5F) and again the house was only 63F. Havent had the problem on warmer days. Attempted resolution: Installer came and checked system on a warmer day -- "OK, no problems - call when it happens again." I am concerned that the system is undersized and I will have to fight this problem every winter on the coldest days. How can I tell if the system is undersized (I dont have confidance in the installer because they stand to lose $ if they have to install a bigger unit). Thanks in advance!