Suburban NT-22 Furnace
The special thing about an RV furnace is the sealed combustion chamber. In other words, the air that feeds the flame comes from the outside as opposed to the cabin’s interior, and the burned fuel gas is exhausted outside. Due to the compactness of the design, a dedicated fan blade blows air through the combustion chamber. This forced air also minimizes hot spots, and increases thermal efficiency. Cabin air is warmed by another fan blade blowing air across the outside of the heat exchanger. One motor spins both fan blades.
Furnaces in 1967 were incredibly simple compared to modern day furnaces. Only two relatively simple repairs were necessary to bring my furnace back online: Cleaning the pilot light jet, and addressing an old recall notice:
From the Internet:
Suburban initiated a recall for all furnaces made from 1966 through 1977:
Campaign : 77E-012 initiated summer of 77
Campaign : 81E-015 initiated winter 81-82
The furnaces were models NT-17, NT-20, NT-22 and NT-30 manufactured between 1966 & 1970 The serial numbers were 0064881 and lower. Also furnaces made between 1970 & 1977 except those with an "M" suffix, The serial numbers are: 0064881 through 0715865. The recall specifies:" if the model and serial number of your furnace falls within those noted, have it inspected unless you are VERY SURE the Suburban recall has already been completed on your unit. The furnaces in question have a rubber-like crossover tube that could crack. Extremely dangerous carbon monoxide would then be expelled into the interior.”
The first interesting thing about this recall is that I never found a serial number on either my original, 1967 NT-22, or the 1972 NT-22 parts furnace a friend gave me. But, after inspection, I found my furnace would have been subject to the recall. The parts furnace would not have been:
I do not know if Suburban relocated the combustion chamber blower just so they could incorporated a metal crossover tube. But that is one of many subtle differences between the two units pictured above.
The second interesting thing was crossover tube’s function. The tube directs outside air from the blower into the combustion chamber. A leaky tube would only allow cold outside air to be forced into the interior. I suppose if the tube split & fell off, there could be a concern about not enough air feeding the flame. The furnace would probably get hot enough to trip the over-temp sensor. But the tube has such a short run (2-3 inches), that even then I am not sure there would be a concern.