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Posted by Doug B on March 28, 2008 at 08:28:08:
I've been researching to upgrade my current 65 year old boiler, It's a National Radiator Company A-104 Oil Fired hot water Monster that still performs well but is extremely inefficient. It has a 10 year old Becket Burner, and a domestic coil. The house, built in 1941, is only 1100 sqft, but has cast iron radiators throughout. All the radiators have been sanblasted and restored, and don't leak, plus they give a nice even heat to the home, so I plan on keeping them. According to the tag on the boiler, it has a input of 130 mbtuh, and an output of 86 mbtuh, giving it an approximate efficiency of 65%, and burns 1.10 gph of fuel oil. The design is an upfeed sigle loop sytem with a 1" copper pipe main, and 1/2" copper branches at each radiator. The braches are all connected with standard copper "T"s in stead of the usual "monoflow" "T"s, which I thought was a bit strange.
After doing preliminary EDR calcs on the current radiators, my load factor is approx 55,00 btuh, not including the domestic water usage. Two of my rooms are constantly cold, and after doing the calcs, realized that the radiators are too small in those two rooms. If i figure new larger radiator for these two areas, my new load is approx 68,000 btuh with out any factors of overdesign safety.
My first choice for a replacment would be a Burnham MPO84 giving me 74 mbtuh at .6 gph and a Superstor SSU45 IFWH for domestic HW. The specs on the IFWH say to use a 141MBTUH boiler for 180 deg water. Is this little 74Mbtuh boiler going to be enough to run this 45 gal IFWH? or should i bump to the MPO147?
Another hiccup to add is that i would like to change from a single zone house, to 2 zones, preferably 3. If i split to 2 zones each zone would have 27mbtuh, and 41mbtuh. If i change to 3 zones each would be 38mbtuh, 27mbtuh, and 14mbtuh. Unfortunately i think i go to 3 zones, i would probably need a buffer tank for the smallest zone to keep the boiler from shorting.
Another question is, when changing from the Old Monster boiler to the new Smaller unit, Will i have thermal shock issues because of the decrease in system water capacity? or would i need to use a buffer tank as well?
What is the general concensus?