Unless someone can properly explain why high 93% efficiency boilers need outside air ventilation intake where as CAST IRON boiller (83% efficient) don't need it:
I believe the only reason is to ****LOWER the flue gas temperature***** and generate condensation which defeats the energy savings purpose (meaning drawing hot air out versus drawing -10F cold air in = same efficiency) since flue gas can only condensate below 130 to 120F???