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In general, and all other things being equal, is a 100,000 btu mod-con firing at 50% power more efficient than a comparable 50,000 btu unit at full power?

Our radiant is clip-finned pex suspended under the floor - it heats the airspace beneath the floor so the design temp is 180 deg, a good match for fin-tube. It's a rather common set-up in this area....

Okay, here's the confirmation I needed. I set the boiler's max CH power at 50%. With all zones calling, it took 22 min to bring the supply temp from 140 deg. to 180, then it maintained 180 at 37%...

Okay, that gives me some assurance that the quick 'n dirty heat loss calc. I did for my house, a new 1900 ft cape and -2 deg design temp, coming in at about 27K BTU is in the ballpark.

I've put...

Hmmmm. Good call. My only defense is that for some reason it looks a lot bigger in the photo than it really is. On the other hand, it wouldn't take much to brace it off the HW tank. Thanks for...

Aside from a min. fire rate of 20KBTU rather than 10, does setting the max boiler output at 50% equal a 50BTU unit? I seem to be doing okay right now with the two 1st floor radiant zones tied...

Won't the circ. pump just draw water from the buffer tank until its' water temp drops enough to fire the boiler? Then the boiler's got to bring 30-40 gal. back up to the hi limit? Or am I missing the...

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Man. This thread has been a real crash course in home heating systems, and I truly appreciate everyone's contributions. I've even been credited with thinking like a wet-head, which I think is a good...

I'm considering doing just that. If I've read the Utica literature correctly, the 50 and 100K BTU models are dimensionally identical, so the swap would be easy. The cost of the boiler wasn't broken...

http://i683.photobucket.com/albums/vv195/Seagull70/IMG_20491_zps4a34df95.jpg

Thank you, Dana. That's a good deal of information to ponder.

Above is my system. The supply and return are 1...

I think I see the problem - I've got a 100000 BTU boiler heating a 27000 BTU house!


House:

2 story saltbox 1900 sq.ft.
built last summer to Energy-Star standards
6" walls, R-50 in attic...

Got it. It's all about insuring the heat exchanger has adaquate flow through it regardless of what's going on in the secondary loop. So then, is this a classic example of the need for a buffer tank...

No, it's not faulting, but simply reaching temp. setpoint, sometimes within 30 seconds and shutting down.

I can't judge whether or not the piping is correct (though the house IS warm today - a...

I'm a homeowner trying to get a handle on my newly installed Utica SSC-100 modcon boiler. It cycles incessantly with short burn cycles.
I don't know how to post the diagram, but if anyone cares...