How does a Buderus 315 gas Boiler compare to a Weil McClain Ultra (same size) in terms of efficiency and performance?
Thanks

((in terms of efficiency and performance))

This information can be found at the manufactures web site. They are just numbers.

The most important thing you can do is to make sure the person that is doing the install really knows whet they are doing with these high eff condensing boilers. Last winter I was involved with some testing of high efficiency boilers at the university lab.

To start with you will need some expensive meters. These units are not set up from the factory to run under all conditions. Gas clocking and CO testing are a must or you will be very unhappy with the amount of efficiency the unit produces.

Gas line sizing had to be watched like a hawk if to small some of the boilers will not run at all due to safety controls. Some venting conditions will also cause problems.

Many of the manufactures will not honor the warranty unless a specialist sets up the boiler when new so that the boiler does not become damaged. Usually a person who has participated in the manufactures classes or a person of long time standing in the boiler trade are accepted as a specialist.

To make a long story short these new high efficiency condensing boilers and not your fathers boilers from years past.