Did you guys notice the increased range of the Lambda Pro combustion numbers. They now have a lower and higher range with oxygen percentages (down to 3.8% from 4.4% and up to 7.3% from 6.9% oxygen) (and corresponding increased/decreased CO2), probably to accomodate the higher modulation ranges offered. Also, Viessmann has a 6.75 to 1 modulation range on the 19,000 to 125,000 BTUH. I guess manufacturers are pushing the limits now a days and the old days of 5 to 1 are gone perhaps? Are the certification agencies bending the rules or was the numbers changed?
Class 'A' Gas Fitter - Certified Hydronic Systems Designer - Journeyman Plumber