Here is a quote from an earlier post concerning problems with Duo Therm Furnace.....
dougrainer wrote:
Duotherm produced the 9000 series and took it OFF the market after a few years, because of intermittent staying lit. It was due to the CASE PRESSURE. A symptom was as you described, Works on the bench AND if you remove or slightly remove the case cover when installed, it lights and stays lit. IF YOU HAVE THIS MODEL, A REPUTABLE SERVICE COMPANY WILL NOT ATTEMPT REPAIR. It would be a waste of time and just cost the customer money. They CANNOT be repaired and be guaranteed to work. There are very few parts and Dometic has not supplied parts for over 20 years. The only sure fix is to replace with a compatible model that will fit in the space. Dometic used to send out NEW units under warranty and they sometimes failed to stay lit. Doug
So it's time to replace.
Biggest question is which furnace..Atwood or Suburban.
You will need to measure available space.........clearances, obstructions, access etc.
Here is a install manual.....pg. 2 & 3 give dimensions.....
LINKMight want to PM 'dougrainer' and ask him which Brand/Model would be easiest to retrofit.
Good luck!