a 3-pass wet back design

[Setwale_Charm]

Can anybody suggest to me what the above might mean in practice?

 

[Old Novice]

It sounds like some pretty specialized vocabulary. Can you give us any more context?

 

[Setwale_Charm]

The sentence is part of the description of a boiler. Which is a 3-pass wet back design where the first pass is a furnace, and the other are small bore tubes.

 

[Kelly B]

Three pass means that the flue gases (the products of combustion of a heater or boiler) are passed back through the heat exchanger three times in order to maximize the heat reclaimed, and minimize the heat lost when those gases are released.