What boiler - not instant units

[Howard]

What type of boilers are people here using and how happy are
you with them. How many BTU/Hr are they and what is your mix
of washers. I need to replace my pre-historic Natco firetube,
and am looking for ideas. I have thought about the Paloma and
other instant on units, but am not convinced that they can work
in my situation. I have too many big machines that need to
draw much more than they can supply. Plus, while many here
rave about them, I have been warned by others to stay away from
them.

My problem is that I have many large machines (75#, 50# and
35#) that draw lots of water at once. It is not uncommon for a
customer to come in and use two 75# machines at once. That
alone will draw 60 gallons of hot water in a two minute period
of time (30gpm). The instant units just cannot handle that.
That does not even include other machines drawing water.

[Charlie]

Well Howard, no one seems to want to tackle this, so I'll jump in. I purchased some used 4 year old HE-270 Hamilton units, with a 220 gallon storage tank. I've only had them a month, but so far I'm pretty happy. These units are about 80-83% efficient according to the factory. Burning 540K BTUs combined, they will heat the 220 gallons from cold to 125 in about 12-14 minutes. The second unit rarely cuts on in actual use.

I was very taken, however, with the new Hamilton super-efficent unit (99%), called the Evolution, which was shown at the Clean Show. These come in 200K BTU units, which can be combined. Saving 15% of the gas cost can repay this pretty rapidly, so I'm thinking that down the road I will pull one of my two HE units to my old Mat, and use the Evolution as my primary heater, with the other HE-270 as the secondary.

I have read, somewhere, maybe the journal, that these new super-condensing units from Hamilton, Natco, and others, are most efficient when they have long run times, and not as efficient in short run times. I don't have any further information, but still think they are worth considering. If you can save 10-15% on your bill, how long would it take to pay off the additional cost?