Twilli wears 'em.
Originally Posted by twilli3967
Thank you all for your wonderful advice. We are weighing all opinions. Comfortdoc, I must say your thoughts are compelling! I am definitely leaning towards the mod/con wallhung. Much appreciated! Thanks for being there, guys! We all value your advice! Marti
Originally Posted by sskzekeman
There is more to be saved than just the 10% indicates.
The source of combustion air is not figured into the rated efficiency numbers. However, this is a big additional savings for the 90% unit.
The modulating burner is also a savings. When it is operating at partial load, even at higher water temperatures, the efficiency goes up. Here is a chart from Viessmann showing this.
Also, since mod cons are low mass with mechanically induced draft, there is so much less heat lost during the off cycles. With a cast iron block on a chimney, whenever the boiler finished firing, there is heat left in the cast iron and water content of the boiler. This heat will go up the chimney during the off cycle. When the boiler fires back up, it has to reheat the block first. (This isn't as big of a factor for Buderus cast iron boilers compared to others since they use a low water content, relatively light block. 230 lbs, 2.4 gal water for the 74k BTU models)
There are reports from people at heatinghelp that document much more than a 10% savings after switching to mod/con. Some even have 30-40%.
To the OP, the Buderus GB mod/con uses an aluminum block. As someone already mentioned, aluminum blocks need a bit more attention to water quality - it isn't necessarily a deal breaker, but something to be aware of. There are also other good mod/con choices. My favorite is the Lochinvar Knight. Stainless Steel heat exchanger, modulates lower than Buderus GB, designed and built in the USA in Tennessee, and less expensive.
Last edited by aemeeich; 11-30-2007 at 12:52 PM.
I think twilli rolls in overalls or he wears no pants at all!